Lawn Care Library
The Essentials

Lawn Maintenance
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Timely Tip

September: Hand weed light infestations of broadleaf weeds. Consider postemergence herbicide in second half of month for heavy infestations.

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Healthy Lawn Overview

Quick tips for a healthier lawn.

You don't have to become a lawn expert to have a healthy lawn. Just follow these simple tips and you'll be well on your way.

Mow high. The shorter you mow your lawn, the more work you will need to do to keep it looking good. Never cut more than a third of the plant when you mow. If you want to keep your lawn mowed to just 1 inch, that means mowing when it reaches 1.5 inches, or every 2 to 5 days. That's a lot of work. Mowing that close can weaken root systems (making the grass more prone to pests and drought), and makes it easier for weeds to outcompete grass. Mowing your lawn to a 3-inch height helps grass outcompete weeds. It means mowing when the grass reaches 4.5 inches, or every 5 to 15 days, depending on growth rates. More on mowing.

Keep your mower sharp. Dull blades tear grass instead of cutting it. Lawns mowed with dull blades use 30 percent more water. Plus the wounds created by dull blades allow disease pathogens to enter grass plants. File your blade regularly, and replace damaged blades.

Leave the clippings. Clippings do not create thatch, contrary to popular belief. If you cut only a third of the plant at each mowing, the clippings won't smother the grass either. Mulching mowers work best to chop up clippings so they can settle down through the grass and onto the soil surface. There, earthworms incorporate clippings into the soil, improving both its drainage after storms and ability to hold water during drought. Do not disperse clippings onto pavement or into gutters. They are high in phosphorus and can cause pollution when washed into storm sewers and reach streams and lakes.

Don't fertilize early. Fertilizing in early spring only stresses grass plants over the long term by encouraging excessive top growth at the expense of roots. (Do not apply fertilizer to frozen or saturated soil, or on top of snow. It's a waste of fertilizer and a sure way to have it wash into streams and lakes.) A better strategy is to fertilize in fall, from about August 15 until about 2 weeks after last mowing. Plants will use this fertilizer to develop root reserves to help them survive through winter and get off to a healthy start next spring. More on fertilizing.

Watch your water. It's easy to do more harm than good. Never water at night. Wet grass invites diseases. Water between 4 a.m. and 8 a.m. when the leaves will dry quickly in the morning sun. During extended drought, stop watering and allow grass to go dormant. More on watering.

Special care in shade. Grass needs a minimum of 4 hours of direct sun -- 6 hours if it gets much foot traffic. Consider other ground covers if your lawn receives less than this. In shady spots, plant fine fescues that are adapted to lower light. Mow high and reduce fertilizer. More on shade.

Spray sparingly. Never use lawn insecticides without scouting to see if the problem justifies treatment. Seventy-five percent of lawn insecticide applications in New York are unnecessary or ineffective. Manage grass for healthy root systems that can tolerate some insect damage and remain aesthetically pleasing. More on insect pests.

Fill in weak spots. Use a rake to work up and improve the soil where weeds flourish or the ground is bare. Then reseed with grass varieties best-suited to the site. If, after a season of mowing high and leaving the clippings (taller grass will help shade out weeds), your lawn is still more than half perennial weeds and bare spots, consider a complete renovation.

Why Lawns Matter

Properly managed, they offer big benefits to people and the environment.

Well-managed lawns are an environmental asset. They can help protect -- or even improve -- water quality.

Poorly managed lawns -- whether by neglect or through the overuse of fertilizers and pesticides -- can be an environmental liability.

What you and your neighbors do with your lawns matters. Collectively, you control about 900,000 acres of lawn -- 75 percent of the managed turf in the state of New York.

It's up to you whether or not that land is used to enhance our environment. It means being aware that small acts -- such as not washing grass clippings into the street or down sewer drains -- can have a big impact on our streams and lakes.

Healthy lawns provide many benefits:

  • Lower air conditioning bills. Moisture evaporating from grass leaves helps keep air temperatures cooler.
  • Less pollution. Lawns can help filter pollutants out of the air and reduce noise pollution, especially when used along with physical barriers.
  • Higher property values. Attractive lawns contribute to the overall appearance of a community's landscape.
  • A place to play. Grasses are the only plants that can stand up to repeated recreational use.
  • Better water quality. The thick sod formed by grasses helps water soak into the ground. This helps reduce or eliminate runoff that can carry soil or other contaminants into waterways.
You can reap most of these benefits without spending very much money or taking more time than you are probably already spending on maintaining your lawn.

Choosing a Lawn Care Service

Ask questions to see which is right for you.

Some communities in New York are served by dozens of lawn care companies. How can you tell which one is right for you?

Here are some questions suggested by several reputable lawn care professionals.

Do they guarantee their service? Many companies guarantee your satisfaction. Ask about the specifics. If they damage your lawn, will they fix it or simply refund your money? Is the guarantee in effect only if you subscribe to their entire service?

How good is their work? If it's good, they will have satisfied customers. Ask for referrals. Find out how long the company has been in business and how many repeat customers they have. (A 20- to 30-percent annual turnover is normal.) How quickly do they respond to complaints? Will you have to pay for follow-up visits? Most companies do not charge for callbacks.

What is their minimum charge? Do they provide a written contract specifying what services they include? New York law requires lawn care companies to provide customers with written advance notice of automatic renewal for services past the first year. Written contracts will also specify the services to be included in the program.

Are they flexible? Will they make adjustments to their routine application schedule? For example, will they skip the early spring fertilization and provide a late fall fertilization instead? If you are willing to tolerate a few weeds, will they skip the pre-emergent crabgrass herbicide and come back later to make a post-emergent treatment if needed?

How do they train their employees? Training time varies from none to several days. All applicators should have a basic ability to identify grasses, weeds, insects, and diseases. They should also know what they are applying, why they are applying it, and the proper way to apply it.

Are the applicators experienced? In the lawn care business, much is learned through experience. Experienced employees are more likely to be able to diagnose problems and take care of them. A company's ability to retain experienced employees provides clues to its professionalism.

Are the applicators certified? State law does not mandate that all lawn care applicators be certified, but many companies are making that their goal. Certification guarantees that the applicators have received some training in safe pesticide handling and have passed a required test.

Does the company have liability insurance? Protect your personal property by requiring proof of liability coverage from the company.

How Grass Grows

Understand cool-season grasses and help them thrive.

Most lawn grasses grown in New York -- Kentucky bluegrass, perennial ryegrass, and fescues -- are cool-season grasses. They grow best in spring and fall.

The major exception is zoysia grass, a warm-season grass occasionally grown in warmer areas downstate. Most ornamental garden grasses are also warm-season grasses.

The roots of cool-season grasses grow best between 55 ° F and 65 ° F. Shoots grow best between 67 ° F and 75 ° F. In early spring, even before the grass starts to green up, the roots break dormancy and begin growing.

The combination of long days, cool temperatures, and adequate moisture produces a flush of growth in the spring. This sometimes makes it challenging just to keep up with mowing. In a normal year, 60 percent of grass growth comes during 6 weeks in spring.

Spring is a good time to seed and fertilize bare spots in the lawn caused by winter damage. Fertilizing healthy lawns at this time, however, just increases topgrowth (and mowing chores) at the expense of root growth. This lush, succulent growth encouraged by spring fertilization makes grass more susceptible to insects and diseases. Plants with smaller roots are also more vulnerable to drought later in the season.

As temperatures warm during summer, growth slows and lawns require mowing less frequently. Roots can be damaged when temperatures are above 85 ° F. During this "summer slump," warm-season weeds such as crabgrass (Digitaria spp.) can thrive because they are more competitive in warm weather.

The combination of warm temperatures and lack of moisture can cause cool-season grasses to go dormant and turn brown during dry summers. In most cases, the grasses haven't died. They will green up and grow again in fall when cool weather returns and soil moisture is replenished.

Fall is a good time to fertilize lawns because the nutrients primarily support root growth. They help the plants build up reserves to get through the winter and green up healthfully in spring. That's because topgrowth stops in fall after about 10 days with average daily temperatures below 50 ° F. But roots will continue to grow and take up fertilizer until the ground freezes.

An ideal time to fertilize is between Halloween and Thanksgiving - about 2 weeks after your last mowing. Apply 1 pound of nitrogen per 1,000 square feet. (1 lb. N/1,000 ft.2). Use a fertilizer that is about 70 percent slow-release nitrogen. More about lawn fertilization.

Choosing Lawn Grasses

They're not all the same! If you are renovating or reseeding your lawn, it's important to pick the right kind of grass for your situation. Each of the four most popular cool-season lawn grasses (profiled in the slideshow) has its strengths and weaknesses.
Types of Lawn Grasses

Consider the following before you choose which grass will work best for different areas of your lawn: (See chart below for summary.)

Shade tolerance. Grasses are sun-loving plants. They need an absolute minimum of 4 hours of direct sun a day. Areas that get much traffic require at least 6 hours. If your light is marginal, fescues tolerate shade better than bluegrass or ryegrass.

Drought tolerance. If you don't plan to water during summer droughts, or your soil doesn't retain much water, fescues again are your best choice.

Wear tolerance. Fine fescue does not stand up well to traffic. Chose one of the other species for lawn areas that take a lot of wear and tear.

Establishment. Perennial ryegrass is quick to germinate and protect the soil -- an important consideration on slopes that are vulnerable to erosion. Kentucky bluegrass is the slowest to germinate, while the fescues fall between the two.

Growth habit. Kentucky bluegrass spreads by underground stems called rhizomes. It forms a tough sod. When damaged, the rhizomes can creep back in to cover the bare spot. The other grasses are bunch grasses that don't spread as well or form as dense a sod.

Leaf texture. Fine fescue has very thin, fine leaves. Tall fescue's leaves are coarse. Ryegrass and bluegrass fall in between.

You also need to consider how much time and money you plan to invest in your lawn, and how good you want it to look. The fescues are good choices for low-maintenance lawns that you won't have to fertilize often, and that you won't mow closer than 3 inches to the ground.

At the other end of the spectrum, Kentucky bluegrass makes a fine-looking lawn, but requires more careful management to stay healthy. Plan to fertilize it three or four times a year, and keep in mind that it is more susceptible to drought and pests.

When you purchase grass seed, it is often a mix of several species. Read the label to find out what's in the bag before buying. "Variety not specified" on the label means "buyer beware".

Try not to purchase a mix that is more than 20 percent perennial ryegrass. Because it germinates quickly, ryegrass will overwhelm the other species if there is too much in the mix. (Also avoid annual ryegrass. It will germinate and grow quickly, but usually dies over winter.)

Some typical mixes matched for different situations:

Sunny, medium- to high-maintenance lawn:

  • 65% Kentucky bluegrass blend (several different varieties)
  • 15% perennial ryegrasses
  • 20% fine fescues

Seed at 3 to 4 pounds per 1,000 square feet.

Sunny, low-maintenance lawn:

  • 65% fine fescue blend
  • 15% perennial ryegrasses
  • 20% Kentucky bluegrass blend

Seed at 4 to 5 pounds per 1,000 square feet.


  • 100% tall fescue blend

Seed at 7 to 10 pounds per 1,000 square feet.

Shady areas:

  • 100% fine fescue blend

Seed at 4 to 5 pounds per 1,000 square feet.

Summary of cool-season lawn grasses
Kentucky Bluegrass
Perennial Ryegrass
Tall Fescue
Fine Fescue
Shade tolerance
Drought tolerance
Wear tolerance
30 to 90
14 to 21
Ave. to Fast
21 to 30
21 to 50
Growth habit
Seeding rate
(lb./1000 sq. ft.)
1 to 2
5 to 9
5 to 9
3 to 5
Nitrogen fertilizer
(lb. N/1,000 sq. ft./year)
3 to 4
2 to 6
2 to 4
1 to 2


Mow high, mow often, and leave the clippings.

Proper mowing gives grass a competitive advantage over weeds and helps keep your lawn healthy. Over the course of the season, mowing is the single most time-consuming lawn-care chore. You may as well do it right!

How high? For a healthy, low-maintenance lawn, set your lawn mower to trim grass to a 3-inch height or higher. This is because the roots underground mirror the shoots on top. The shorter you mow, the smaller the root systems.

Small root systems leave your lawn more vulnerable to drought, insects, and invasive weeds. Short lawns also require more frequent fertilization. Longer grass helps cool the soil surface, reducing water loss from the soil and decreasing competition from warm-season weeds, such as crabgrass.

How often? It depends. Let the grass be your guide, using the One-Third Rule: Never remove more than one-third of the grass blade when you mow. That means if you are cutting your lawn to a 3-inch height, you should mow before the grass is more than 4.5 inches tall. During the spring flush, you may need to mow every 3 to 5 days. During the summer slump, the interval may be two weeks or more. If you are cutting the grass shorter, you will need to mow more often.

When to start? Start mowing in spring when the One-Third Rule says it's time: When the grass reaches 4.5 inches if you are maintaining a 3-inch cut. Stop mowing in fall as growth slows, usually about the time that the daily average temperature falls below 50 ° F for a week. Don't leave the grass more than about 4 inches long because it can mat down and encourage snow mold.

What about the clippings? Leave them. They do not cause thatch, contrary to popular belief. (Thatch usually occurs only when turf is excessively fertilized and soil is compacted, cool and moist.) If you follow the One-Third Rule, they won't smother the grass plants. They will quickly dry out and work their way down to the soil surface where earthworms will help incorporate them. Mulching mowers chop clippings finely to speed the process.

The clippings return nutrients to the soil, so you need to fertilize less. They can also cool the soil and help it retain water. Do not blow or leave clippings where they will wash into streets or sewer drains and end up polluting our waterways. Clippings are high in phosphorus, a major non-point source pollutant. If you have a lake, pond, or stream on your property, establish a natural buffer zone between your lawn and the water. Allow the vegetation to grow long in the buffer so that clippings don't get into the stream. The buffer can also filter out other potential pollutants.

Anything else? Keep your lawnmower blades sharp. Dull blades tear the grass instead of cutting it cleanly. The wounds cause the grass to lose more water, increasing irrigation needs or moisture stress, and also leave the plants more vulnerable to diseases.


Use only what you need, and avoid spring applications.

Just like people, lawns need a balanced diet, too. If you feed them too much, too little, or apply the wrong kind of fertilizer, they won't be healthy. When you fertilize is critical, too. (Fall is better than spring.)

Test your soil. A soil test will tell you how much (if any) phosphorus (P) and potassium (K) fertilizer your lawn needs. Contact your local extension or the Cornell Nutrient Analysis Laboratory for more information.

If tests indicate that no P or K is needed, use nitrogen fertilizer sources that contain little or no P and K.

Adjust pH, if needed. Lawns should have a slightly acid pH, between 6.0 and 7.0. If your soil tests fall outside of this range, follow instructions for adding lime or sulfur to bring pH into this range.

Focus on fall. If phosphorus and potassium levels are adequate in the soil, nitrogen (N) is the most important nutrient for grass growth. Understanding how grass grows is important when making decisions about how much and when to apply nitrogen fertilizer.

For most low-maintenance lawns, a single application (1 lb. N/1,000 square feet) between Halloween and Thanksgiving (about 2 weeks after your last mowing) is the best time. Most home lawns with modest expectations do just fine with a single late-fall fertilization.

Do not fertilize during "Indian summer" - a warm period following hard frost. This may cause excessive topgrowth, reduce root storage and increase winterkill. The best window for fall application is after topgrowth stops, usually after 10 days with average daily temperatures below 50° F. Roots will continue growing and taking up fertilizer until the ground freezes.

Organic nitrogen sources are not a good choice for fall fertilization because they require warm soil and microbial action to release nitrogen. Soluble nitrogen sources are readily available to the plant, but on sandy soils there is the risk of leaching. A 50%-50% or 70%-30% mix of slow-release to quick-release N is less risky to the environment.

For higher maintenance lawns, you can also apply 1 lb. N/1,000 sq. ft. around Labor Day and/or Memorial Day. Avoid early-spring applications. Research shows that these applications do not really enhance spring green-up compared with late-fall applications. (Neglected lawns or sods thinned by winterkill may benefit from .5 lb. N/1,000 sq. ft. after the soil has thawed and drained but before the grass greens up.) At least 50 to 75 percent of the nitrogen applied to any lawn should come between the months of August and November.

Fertilizing healthy lawns in spring just increases topgrowth (and mowing chores) at the expense of root growth. The lush, succulent growth encouraged by spring fertilization makes the plant more susceptible to insects and diseases. Plants with smaller roots are also more vulnerable to drought later in the season.

Lawns that did not receive fall fertilizer applications or have suffered from winter injury may benefit from spring nitrogen applications. But wait until soil temperatures have warmed to at least 55° F before applying.

Water it in. Give your lawn a quarter- to a half-inch of water after spreading fertilizer to get the material into the ground where it can be used by plants.

Consider the source. Most synthetic lawn fertilizers contain at least 40% slow-release nitrogen. Slow-release N becomes available to the plant over a period of time depending on soil moisture, temperature, and microbial activity. The balance of the N is water soluble nitrogen, which is readily available for plant uptake.

In addition to supplying N over a longer period of time, slow-release nitrogen sources have a lower risk of burning plants and a lower potential to pollute water than water-soluble N sources. The tradeoff is that slow-release N is usually more expensive.

Natural organic fertilizers supply nitrogen in complex organic forms that are not immediately available to plants. They require warm, moist soils for microbial activity to release N. Natural organic fertilizers are well-suited for applications during warm summer months when the potential for burning plants with high-salt synthetic fertilizers is higher.

Lawns grown on mostly sandy soils should rely more on slow-release nitrogen to reduce the possibility of N leaching out of the root zone. Research shows that on most soils with some silt and clay, nitrogen leaching from lawns is rare.

Consider different needs. High-traffic areas usually require more fertilizer than low-traffic areas. Different species of grass have different needs, too. Kentucky bluegrass, for example, requires more nitrogen than fine leaf fescues.

If bluegrass doesn't get enough N, it is less competitive against weeds and pests. If fine leaf fescues (which normally grow slowly) get too much N, they produce lush, weak growth that is susceptible to pests.

Apply with care. The whole idea is to get the right amount on the lawn and none in our streams and lakes. Rotary spreaders cover a wide swath, but they can also hurl fertilizer into streets and driveways where the next rain carries it into storm drains and then on to waterways. A drop spreader may take a little longer, but it puts the fertilizer exactly where you want it. Use care when loading spreaders. Sweep up spills before they become a pollution problem.


Careful. You can do more harm than good.

Most lawns in New York rarely need watering, except possibly for a few weeks in summer. Foregoing watering during these weeks does not mean that you can't still maintain a healthy turf. But it does mean careful preparation before this period of moisture stress.

If you do choose to water, it's important that you water properly. Poor watering practices can do more harm to your lawn than good, and it can carry pollutants out of your yard and into waterways.

When? Never water at night. The best time to water is early in the morning, between 4 a.m. and 8 a.m. Evaporation is low at this time so more of the water makes it into the soil. Also, leaves will begin drying quickly in the morning sun, reducing the chances of diseases. Avoid watering on cloudy days.

How much? It's tough to say. It depends on the soil type, cutting height, lawn use, temperature, wind, and a host of other factors. In general, a healthy lawn loses about 1 inch of water per week during summer. (The water lost from the soil through the leaves and through the surface of the soil is called evapotranspiration, or ET.)

If you receive an inch of rainfall every week through summer, chances are pretty good that your lawn should come through with little moisture stress. If you get less, you can make up the difference with sprinklers or an irrigation system. Your water application rate should supplement what you receive as rain. If you get ½ inch of rain one week, only apply another half inch.

Use a rain gauge, coffee cans, or other containers to measure rainfall and supplemental water.

It's also important not to apply water faster than your soil can take it up. How fast your soil can absorb water is called its infiltration rate. When your irrigation rate (how fast you are putting it on with the sprinkler) is higher than the infiltration rate (how fast your soil can soak it up), puddling occurs on level areas. On slopes, the water will run off and can carry sediments and other pollutants with it.

To avoid this, measure your soil's infiltration rate by cutting off both ends of a coffee can and inserting it several inches into the soil. Pour about 1 inch of water into the can and time how long it takes to soak in. Then measure your irrigation rate by placing a coffee can (with the bottom intact) in the area watered by your sprinkler and time how long it takes to fill the can with 1 inch of water. Your irrigation rate should not exceed your infiltration rate.

What about drought? It is normal for cool-season grasses to experience "summer dormancy" in response to lack of moisture. Studies show that as little as ¼ inch of water over a three week period can be enough to keep the sod from dying.

Under all but the most severe conditions, it is better to avoid lawn watering, especially if your watering system isn't precise. Too much or too little supplemental water can weaken plants, making them more susceptible to pest problems and less likely to recover when cool, moist conditions return.

What can I do to prevent water stress?

  • Plant grass species that require less water, such as fescues.
  • Mow grass higher, encouraging larger root systems.
  • Avoid spring N fertilizer applications.
  • Leave grass clippings.

Dealing with Leaves

Keep them out of storm drains and waterways.

Leaves are loaded with phosphorus. If they are not managed properly when they fall from trees in autumn, they can end up in surface runoff. When that runoff flows into waterways, the phosphorus in the leaves can cause algal blooms, lower the level of dissolved oxygen in the water, and kill fish and other aquatic organisms.

If you have a lot of leaves and leave them on your lawn, they can mat down and smother the grass over winter, leaving large bare patches that are vulnerable to erosion in spring.

Here are some leaf options that can help you have a healthy lawn while also protecting the environment:

  • If the leaves aren't too thick, simply mow them into fine pieces that are small enough to filter through the grass to the soil surface where they can help improve the soil. A mulching mower works best.
  • Collect grass clippings and leaves for composting. A mix of one part clippings to three parts leaves works well. Make sure your pile is located where the leaves won't blow or wash away. Turn the pile occasionally to speed decomposition. Use the compost in your garden and flower beds.
  • If you don't have a good place to compost leaves, bag them for collection by your local municipal composting operation.

The most important thing to remember is to keep leaves out of waterways. That means not raking them into the road where they can wash away, or into storm sewers where they can be carried into rivers and streams.

Coping with Shade

What to do when there's not enough sun.

Grasses are sun-loving plants, for the most part. For healthy growth, lawn grasses need at least 4 hours of direct sun a day. If they receive much traffic or wear and tear, they need a minimum of 6 hours.

The shade line changes from month to month, depending on the angle of the sun.

In addition to being weak from lack of sun, grass in shady areas can suffer more diseases because of cool, moist conditions and lack of air circulation. Poor grass stands in shady areas are vulnerable to erosion, which can carry sediments and other pollutants into surface water.

Here are some options for coping with shady areas:

Choose the right grass. In spots that get marginal light, plant fine fescues, which are more shade-tolerant than other lawn grasses.

Grow other ground covers. Grass isn't your only choice. Consider attractive and vigorous shade-loving groundcovers such as:

  • Pachysandra
  • Lily of the valley
  • English ivy
  • Periwinkle
  • Creeping myrtle
  • Sweet woodruff

Plant a shade or woodland garden. There are hundreds of herbaceous perennial flowers and foliage plants that will thrive in shade, as well as annuals such as impatiens.

Mulch around trees. If you don't have the energy to maintain a shade garden, consider using about 3 inches of wood, bark, or stone mulch around the base of trees. (Don't pile mulch against the base of the tree trunk.)

Build paths. If grass grows fine in your shady areas except where people walk, put in a stone, gravel, or other type of path to concentrate wear and tear in one area.

Mow high. Grass in shady areas should be allowed to grow taller than grass in direct sun. Do not mow any closer than 3 inches.

Fertilize and water less. Grass in shady areas grows slowly and needs less fertilizer and water.

Let in more light. Remove lower branches and selectively prune other branches or remove entire trees to let in more light.

Relieving Thatch

Clippings aren't to blame. Thatch is a layer of dead and decomposing plant tissue that forms above the soil. A thin layer (½- to ¾-inch) is beneficial. It protects plant crowns and reduces compaction.

But if the layer gets too thick water, air, and fertilizer can't get through to the soil and grass roots. Runoff increases and dry spots appear. When it's wet, the thatch can remain saturated and suffocate roots.

Leaving grass clippings on the lawn when you mow does not cause thatch. Clippings break down quickly in most cases. Thatch is made up mostly of stems and roots that decompose more slowly.

Thatch usually occurs on turf that has been heavily fertilized, and is most common on poorly drained, compacted, and acidic soils. Of the species of lawn grasses, fine fescues are most prone to thatch problems.

Try core aeration. The best way to relieve thatch problems is by core aeration. Contract with a local landscape company for service or check with your local equipment rental center.

A core aerator in action.

Core aerators punch small holes in the lawn, pull out the cores, and leave them on the surface. Core aeration is most effective in late summer when temperatures are starting to cool and the soil is only slightly moist.

After aeration, air and moisture can penetrate the thatch through the holes. Leave the soil cores on the surface to dry. Then rake them to distribute the soil down through the grass to mix with and dilute the thatch. Don't allow the cores to wash away and pollute surface water.

The mixing action of core aeration is similar to that provided by earthworms. Core aeration can also help increase water infiltration on compacted soils.

Managing Lawn Weeds

A dense, vigorous lawn is your best defense.

Weeds are opportunists. They will find bare spots or places where your grass is weak and exploit those problems to their advantage.

Perennial weeds (those that regrow from their roots every year) can spread and make a lawn unsightly. Annual weeds (those that die at the end of the season and come back from seed the next year) can leave bare spots that are vulnerable to runoff.

No matter what weeds you have, the first line of defense is preventive practices. Try these options to get at the root of the problem first, before resorting to herbicides.

Preventive practices

Mow high. Do not mow grass shorter than recommended for the species you grow. Mowing at 3 inches or higher helps grass shade out weeds and encourages a thicker, more competitive turf. See other sections of this site to make sure that you are using the right grass species, fertilizing and watering correctly, and generally doing all you can to encourage healthy grass.

Reduce compaction. Pay special attention to heavily used areas and sections next to pavement. Weeds can gain a foothold in these spots and spread to the rest of the lawn if it is weak.

Repair bare spots by raking in seed in early spring so that the new grass can compete with the weeds that are sure to come up.

If lawn is thin, fertilize to improve density.

Hand weed. This is easiest when the soil is slightly moist. Check your garden center or catalogs for tools that help get tough perennials out by their roots.

Let the weeds be your guide. If weeds dominate an area, it's likely that there is something wrong with either the growing conditions or your lawn practices. Dense stands of prostrate knotweed (Polygonum aviculare) are a good sign of soil compaction. Don't just pull out the weeds. Relieve the compaction. Violets (Viola spp.) are a good sign of low light levels. One solution might be to seed shade-tolerant fine fescues.

If you use herbicides...

  • Use the right product at the right time. Follow label directions and keep accurate records.
  • Choose products that have the least potential for leaching into groundwater. More highly water-soluble materials have the highest potential (e.g. 2,4-D, dicamba, MCPP).
  • Use extreme caution when handling materials close to wells and impervious surfaces where runoff may enter storm sewers.
  • To avoid volatilization and drift, which release pesticides into the air, do not spray when temperatures are high or it is windy.
  • To help prevent polluted runoff, do not apply pesticides when heavy rains are expected or the ground is already saturated or frozen.
  • Empty containers should be triple rinsed and disposed of properly. Unused materials should be returned in the original container to authorized hazardous materials collection sites.

The types of herbicides include:

Pre-emergence herbicides:

  • Most common for crabgrass and goosegrass.
  • Applied to soil before weeds are expected.
  • Have low solubility and bind to organic matter. Have high runoff potential if not watered in properly.
Postemergence herbicides:
  • Most common for perennial broadleaf weeds.
  • Applied after weeds have emerged and are actively growing.
  • Have high solubility and do not bind to organic matter. Have high leaching potential. Avoid application before irrigation or rain.
Nonselective herbicides:
  • Kill or injure all plants they come in contact with.
  • Used to kill vegetation before reseeding.

Annual grass weeds
Crabgrass and goosegrass are two of the most common grass weed. Both are warm-season annuals. They thrive when temperatures are hot and cool-season lawn grasses are least competitive. Still, they have a tough time invading a healthy lawn.

Annual weeds can easily gain a foothold along paved areas such as driveways and sidewalks where high temperatures can damage cool-season grasses.

You can spot treat for crabgrass with pre-emergence herbicides. These herbicides work on the seeds as they germinate. Because they are ineffective on ungerminated seeds or established plants, timing is critical.

The best time for pre-emergent treatment of crabgrass is about the time that forsythia blooms wane, when the soil temperature is between 59° F and 65° F.

Pre-emergence herbicides do not distinguish between weed seeds and lawn seeds. So you won't be able to replant grass where you've applied them for 2 to 6 months. The other drawback is that you need to apply them before you know for sure if you are going to have a weed problem.

Once crabgrass emerges, usually from early June through mid-July, you can apply postemergence herbicides. Several different herbicides are on the market that can kill plants that have not yet tillered in a single application.

Selective post-emergence control is limited once crabgrass plants develop more than three tillers. Spot treating with non-selective herbicides such as Round-up® can kill the plants and reduce their contribution to next year's seedbank. You must use care not to accidentally spray and kill other plants nearby.

Annual Bluegrass
Annual, indicates compaction

Perennial broadleaf weeds
Unlike those for annual grass weeds, herbicides for broadleaf perennial weeds are usually applied post-emergence. The advantage of post-emergent control is that you can see how many weeds you have before you decide whether or not to spray. If you just have a few, pulling them by hand might be your best option.

Most broadleaf perennials -- such as dandelions -- have their greatest visual impact in spring. But late summer to mid-fall is the time to control them with herbicides. As the weather cools, these weeds start storing food produced by their leaves in their roots, just like cool-season lawn grasses. If you apply an herbicide at this time, it will be transported along with the food and stands a better chance of killing the root.

When applied in spring, these herbicides often kill the tops but not the roots. Because the weed is more focused on producing new growth and flowering at that time, not enough of the material is transported to the roots to kill them, and the weeds bounce back later in the season.

Make sure you choose a selective broadleaf herbicide - one that kills only broadleaves and not grass. Nonselective herbicides, such as Round-up ®, can kill all plants they come in contact with.

Ground Ivy

Managing Lawn Insects

Most pesticide applications made to home lawns are either unneeded or ineffective. To make sure you need a pesticide, you must first "scout" for pests to see if there are enough to justify the treatment. (See Lawn pest profiles for more scouting information.) If you do treat, you need to make sure you apply the pesticide correctly and at the right time.
Pest Profiles

For example, treatment for Japanese beetle grubs isn't justified unless there are more than 10 grubs per square foot. Unless someone peels back the sod at several locations and checks to see how many larvae are feeding on grass roots, you won't know if the pesticide is needed.

By spring, grubs are usually too mature to be controlled by pesticides. Scout for grubs in late summer and early fall to determine if treatment is necessary while next year's grubs are still small enough to control. (If treatment is justified, August is usually the best time.) Because grubs feed below-ground, insecticides need to be watered in before they dry on grass leaves to be effective.

Similarly, scout for surface feeders (such as cutworms, sod webworms, chinch bugs, and bluegrass billbugs) before treating.

Regardless of the pest, the best way to minimize damage is through prevention:

  • Keep turf healthy through proper mowing, watering, and fertilizing. Healthy turf will tolerate more pests.
  • Plant the right grass for your location. Choose grasses that resist pests, such as endophytic varieties of perennial ryegrass and fine leaf and tall fescues. (Endophytes are beneficial fungi that live on the grass and discourage surface feeders.)
  • Scout before you treat. If you use pesticides, treat when the pest is most vulnerable, and follow all directions carefully. To prevent water pollution, never apply pesticides when ground is frozen or saturated. To prevent drift and volatilization (which releases pesticides into the air), do not apply when temperatures are high or it is windy.

Preventing Lawn Diseases

When you see disease, it's too late. By the time you see a lawn disease, it's really too late to do much about it -- at least in the short term.

Common Diseases

Lawn diseases are caused by plant pathogens, usually fungi. The fungi are almost always around, living off dead and decaying material in the soil. You just don't notice them because the grass usually fends them off. (They are not dangerous to people.)

But when the environmental conditions are right (usually plenty of moisture and the fungi's favorite temperature) and your grass is stressed, the scale tips in favor of the pathogen. The result? Check out pictures of these common lawn diseases.

Preventing disease problems is the best strategy, because once symptoms are visible, chemical rescue treatments aren't recommended for home lawns. Prevention means maintaining a healthy turf through proper mowing, watering, and fertilizing. In particular:

  • Keep leaves dry. If you water, do it early in the morning so that leaves dry quickly. Avoid watering at night.
  • Avoid overfertilizing. Too much fertilizer can stress plants and leave them vulnerable to diseases.
  • Plant disease-resistant grasses. Choose the right grass for the site.
  • Improve drainage. Poorly drained low spots are particularly prone to disease.
  • Increase air flow. Lawn diseases are more likely where stagnant air collects. Clear underbrush to improve air circulation.

Salt Damage

Look for it along walks, driveways, and roads

Look for bare spots or invasion by salt- and compaction-tolerant weeds along sidewalks, driveways, and roadsides. Soil is sometimes covered with white or yellow crust. Sodium chloride (salt) used for de-icing causes the problem.

Salt damage is often compounded by compaction from foot traffic, auto tires, and piled snow. Even if the damage is not enough to kill sod, it increases stress on the grass, making it more prone to diseases and weed competition. Weak turf in these areas is especially vulnerable to runoff into storm sewers and surface waters.

Kentucky bluegrass is very sensitive to salt damage. Perennial ryegrass, fine fescues, and tall fescue are more tolerant.

To prevent salt damage, avoid plowing or shoveling salt-laden snow onto turf. Apply only enough salt to do the job after you remove the snow. Calcium chloride-based de-icing salts don't cause as much damage as sodium chloride.

Even though it's often suggested, do not use urea or other fertilizers as de-icing salts. They can run off when snow melts and pollute surface and ground waters.

Spring rains may leach salts from the soil if drainage is adequate. If it's dry, you may need to water by hand to flush them out.

If soil is poorly drained, improve it by mixing in organic matter to a depth of 6 inches, or remove soil and replace it with fresh topsoil and reseed. Improve soil before reseeding because salt can prevent germination and damage seedlings.

Repairing Dog Urine Damage

Dog urine damage is often mistaken for disease problems.

Salts in dog urine can kill grass. The damage is easily confused with disease. Look for dead spots with greener grass around the edges. Female dogs and dry, infertile soil make problems worse.

For more on lawn repair, including instructional videos and slideshows, see Turf Guy Rules.
To reduce damage, flush with water immediately after dogs urinate or train them to go elsewhere. Rake up feces to prevent them from smothering and killing grass, providing an opening for weeds to get a foothold.

Renovation and Establishment

Late summer or early fall is the best time to get your turf in shape for next year.

Before you decide to renovate your lawn, try using the best mowing, watering, fertilizing and weed and pest management practices for a year or two. Pay special attention to problem areas and rake up and reseed bare or weed-infested spots.

For more on lawn renovation, including instructional videos and slideshows, see Turf Guy Rules.

If your lawn is still more than 50 percent weeds after a few years, it might be time to consider a complete renovation. Planning is critical because during renovation your soil is unprotected and can easily be washed away into surface waters.

Late summer or early fall is usually the best time to establish or renovate cool-season grass lawns in most of New York. (August 15 to September 25, or as late as mid-October downstate and on Long Island.) Temperatures are moderating, weeds are less competitive, and moisture is usually adequate.

Follow these 12 steps carefully:

1. Control perennial vegetation.

This step will keep other species from competing with your new grass.

The most effective way to eliminate existing weeds and turf is with non-selective herbicides that contain the active ingredient glyphosate (Round-up ®, for example). Other non-selective herbicides include glufosinate (Finale ®) or the herbicidal soap formulation Scythe ®. Keep traffic off the grass until the herbicide dries on the leaves.

These herbicides are designed to kill any plant on contact but do not kill weed seeds. Once in contact with the soil theys are inactivated. This permits planting the new lawn just 5 to 7 days after spraying.

To ensure an effective kill, wait until the vegetation appears chlorotic (yellow). Then either till the vegetation into the soil, or run a slicer or dethatching tool over the killed sod.

2. Protect and test soil.

Minimize cultivation and compaction to maintain good soil structure. If the site needs grading, this might mean removing and temporarily storing the topsoil.

Before establishing the final grade with the topsoil, have it tested by a reputable soil testing lab. The information the lab provides will tell you how much fertilizer, organic matter, and other amendments are needed to establish a healthy new lawn. Allow two to three weeks for test results.

3. Establish a rough grade.

Take care of grade problems before you replant. Now is the time to eliminate low spots and take care of other drainage problems. Gently grade steep slopes to make mowing easier. Fracture compacted subsoil layers to help water move down through the soil profile.

4. Amend and grade topsoil.

Cover the subgrade with at least 4 inches of topsoil. Ideally, the interface between the subgrade and topsoil should be gradual, not abrupt. Till a few inches of topsoil into the subsoil, then add the remaining topsoil to the surface. If the topsoil is high in clay, add compost materials that are good soil conditioners and have relatively high amounts of nitrogen and phosphorus. These include:

  • Biosolid composts such as Milorganite ®.
  • Brewery by-product composts such as Allgro ®.
  • Animal-manure and yard-trimming composts such as Erthrite ®.
  • Paper-mill by-product composts such as Glatco-lite ®.

Sandy soils can be amended by incorporating a small amount of clay or organic material to enhance water- and nutrient-holding capacity. Add high-phosphorus starter fertilizer with about 1 lb. N/1,000 square feet and/or pH modifiers such as lime or elemental sulfur based on information from your soil test.

5. Choose the right grass.

The species and variety you choose will depend on:

  • The quality of sod you expect.
  • How much work you want to do to maintain it.
  • How you plan to use it.
  • The characteristics of the site, including the amount of sun.
  • Winterhardiness.
  • Resistance to insects and diseases.

See Choosing lawn grasses for more information.

Planting seed costs less than sodding. But use sod instead of seed when rapid turf cover is needed -- for example on slopes that need to be protected from erosion. Most cool-season sods are improved Kentucky bluegrass varieties because their spreading rhizomes intertwine to form a strong sod. Use high-phosphate starter fertilizer when laying sod, just as you would with reseeding.

Keep sod in shade so it doesn't dry out, and install it as soon as possible. Lay it in a staggered brick-like fashion, matching the edges closely.

6. Seed at the right rate.

The larger the seed, the higher the seeding rate. Studies show that there is no benefit from seeding more than the recommended rate. Excessive seeding rates create too much competition between the seedlings. Seeding at the correct rate or slightly lower encourages tillering - lateral spreading of the grass plants. (Sometimes if conditions are less than ideal, a higher seeding rate may be justified.)

Use a drop spreader or rotary "spin" seeder calibrated to deliver half of the recommended seeding rate. Then apply the seed in two different directions at right angles to each other. This assures more uniform coverage.

If you are reseeding a small patch, you can mix 1 part seed to 3 parts soil in a bucket and then spread the mix over the patch. This will help you spread the seed evenly. Ideally, you should end up with about 15 to 20 seeds per square inch.

See Choosing lawn grasses for more about seeding rates of different grass species.

7. Rake lightly.

Mix the seed and soil so that the seed is covered no more than 1/16 to 1/8 inch deep.

8. Firm the soil.

Light rolling assures good seed-to-soil contact needed for the seeds to take up water and germinate. (For small patches, just firm with your feet.) Do not overfill the roller as it may crush seed and cause compaction. A properly rolled seed bed can reduce establishment time by as much as two weeks.

9. Mulch.

Use weed-free straw or marsh hay to conserve moisture and help prevent erosion. (Avoid pasture hay as it is often loaded with weed seeds.) Other effective mulching materials include products made from wood fiber, excelsior, newsprint and other kinds of erosion-control blankets. Products made from a combination of pelletized newsprint, and water-absorbing gel such as PennMulch® are also effective.

10. Water.

Germinating seeds and young seedlings will quickly die if allowed to dry out. Keep seedbeds moist at all times until seeds emerge. Water only enough to moisten the surface. Do not overwater, causing runoff. Gradually reduce water after seedling emergence to encourage deeper rooting. Once grass covers about 60 percent of the ground, the surface should be allowed to dry.

11. Fertilize.

About 2 to 3 weeks after emergence, apply about 1 lb. N/1,000 square feet. This will increase shoot density and the seedlings' ability to withstand diseases such as rust.

12. Mow.

Once more than 60 percent of the grass reaches the recommended mowing height (at least 2 to 3 inches), start mowing. Mowing encourages lateral shoot development, increases stand density, and helps the turf out-compete weeds. Make sure your mower blade is sharp. Dull blades will tear young seedlings from the soil.

Be sure to study up on the best ways to mow, water, and fertilize to keep your new lawn healthy.

What's Wrong with This Image?

Test how much you know about lawn care practices that help keep our waters clean.

What's wrong with this image? Nothing! It illustrates several good lawn care practices that prevent pollution. Compare it with this image:

The bottom image shows at least eight common practices that cause pollution.

How many practices that can pollute our surface- and groundwater can you spot? Answers are below. (Don't peek.)


  • Grass clippings are blown into the street and the storm drain. From there, they are washed into surface waters, where their high phosphorus levels can pollute streams, rivers, and lakes. The mulching mower in the top image returns the clippings to the lawn where they belong.
  • Leaves raked into the street also end up in the storm drain, causing pollution.
  • The boy using the rotary spreader leaves fertilizer on paved surfaces where it will get washed into the storm drain, causing pollution. The drop spreader in the top image is a better option.
  • Weak turf by the corner of the driveway leaves soil unprotected. Sediment can wash into the storm drain, causing pollution.
  • The sprinkler left unattended overwaters the "dog walk" area. In the top image, the girl cleans up after dog promptly, before feces can damage turf or get washed into the storm drain.
  • The woman overwaters the lawn, causing runoff down the driveway. In the top image, she is using a coffee can to measure how much water will infiltrate into the lawn before runoff occurs. That way, she can calculate how long she can run sprinklers without overwatering.
  • Fluids from the leaky van and improperly stored products in the garage are washed down the driveway and into the storm drain.
  • The downspout from house discharges into the driveway, washing pollutants and soil from weak turf along the edge of the driveway into the storm drain. A better option is to discharge in a spot where the water can soak into the soil while moving away from house (as in the top image).

During each of the four seasons there are things you can do to promote a healthy, environmentally sound lawn. Sign up to receive a monthly email containing timely tips for lawn care. See an excerpt from this month's tips below.

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Timely Tip


Late August and September are good times to rake up and reseed bare patches in your lawn. (If you live downstate or on Long Island, this period extends to mid-October.) If your lawn is more than 50 percent weeds, consider a total renovation.

Wait until Labor Day or later until plants recover from summer stress before fertilizing. At least 50 to 75 percent of home lawn fertilizer applications should be made between Labor Day and Thanksgiving. Around Labor Day is a good time to apply 1 lb. N/1,000 square feet to encourage strong roots for overwintering. A single fertilization later in fall is all many home lawns need.

Late July through September is a good time to scout for grubs to see if there are enough to justify treatment. Treating for grubs in spring as they near maturity is often not effective. Pesticide applications, if needed, should be while the grubs are still young and vulnerable. Sometime in August is usually best. Shaded Kentucky bluegrass lawns established more than 15 years ago are most susceptible to grub damage.

Continue to follow the “One-Third Rule,” never removing more than one-third of the plant. (If you set your mower to mow at 3 inches, mow before the grass reaches 4.5 inches tall.) As temperatures cool, grass growth should speed up (if moisture is adequate) and you’ll need to mow more often than you did in summer.

Healthy growing lawn needs about 1 inch of water per week. Use a rain gauge or coffee can to measure how much you receive. If it’s less than an inch, you can water to make up the difference.

Weed Control
Post-emergent herbicides are particularly effective on broadleaf weeds in fall. That's because the weeds are storing up nutrients for the winter, and move the herbicides down into the roots along with the nutrients, giving a better kill. If ground ivy (creeping Charley) is a problem, any product with 2,4-D can provide good control when applied immediately after the first frost. Avoid applications when temperature is below 50 F or before an expected rainfall.

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