Peaches, plums, cherries and apricots are known as "stone fruits" because they have similar hard "pits" or stoney seeds. Native wild plums and cherries were gathered by the Iroquois and Algonquins, and the other common stone fruits have been grown for more than 300 years in New York State, but they are a minor part of our important fruit industry.
Skill and luck are both required to harvest a good crop of these fruits in New York, because we are at the northern edge of their suitable climate region. Winter and spring cold injury to the flowers, buds, roots and trunks is common. Many of our soils are too shallow, wet or infertile for stone fruits, and there are several diseases and insects likely to damage the trees and fruit.
Despite these problems, many New Yorkers take a chance on these fruit crops, because the rewards are great when you beat the odds! Ripe stone fruits are delicate and perishable, so they taste best when they are grown, marketed and consumed locally. For those who think the risks are worth the rewards of home grown fruit, here are some suggestions to improve your chances of success.
Peaches are the least winter hardy stone fruit; flower buds are often killed by winter temperatures below -15° F, and entire trees can be killed below -25° F. Only a few regions in New York have winters usually mild enough to be safe for peaches--along the deep Finger Lakes and Great Lakes, on Long Island, and in the lower Hudson Valley.
The other stone fruits are more resistant to winter cold--almost as hardy as apples. However, all stone fruits are prone to frost injury during bloomtime, because they flower a few weeks earlier than apples. The hazards of deep-freeze or spring frost injury increase at sites farther away from the major lakes, northward, and upward in elevation.
The safest sites are on slopes near the lakes or along valley side-slopes, but not on bottom lands where coldest air often settles. Protected microclimates against south-facing slopes or walls of substantial buildings also provide some relief from cold, but the daily temperature fluctuations in these microclimates can be extreme, which creates additional problems for the trees. Stone fruit trees have rather thin bark, and a protective coat of white latex paint on trunks and lower branches is helpful to prevent "sunscald" or "southwest injury" caused by rapid temperature oscillations on clear, cold winter days.
Some varieties are more cold-tolerant or bloom later than others. The popular 'Redhaven' peach has proven its ability to survive northeastern winters since it was introduced back in the 1940s, and it produces fruit of good quality. About a dozen newer peach and apricot varieties have been developed by Canada's Harrow Research Station--they all have names beginning "Har-" (for example, 'Harrow Diamond', 'Harcot', 'Harbrite', 'Harrow Beauty'). These are excellent varieties for home growers, because they were selected for good fruit quality, cold hardiness and improved disease resistance.
Stone fruits are notoriously fussy about soil moisture and fertility. Where the soil is saturated for long periods during the dormant season, or for more than a few days continuously during the growing season, trees will not thrive.
The best sites are upland gravelly or sandy loams. Soils with high clay or silt content can be improved somewhat for stone fruits by installing sub-soil drainage lines or surface water diversion ditches. Mounding up the area where trees will be planted into raised beds several feet above grade is also helpful.
Peach trees require ample soil nitrogen and water during the growing season. It is essential to keep them growing vigorously because most of their fruit is produced in lateral buds on one-year old shoots. Water during the month before harvest is also important to develop adequate fruit size.
Since most stone fruits ripen during mid to late summer, there is often a long post-harvest period when you can let a few weeds grow and the soil dry out periodically to "harden off" the trees. This moderate stress will slow down the new shoot growth in early autumn, allowing the woody shoots, trunk and roots to store carbohydrates and other nutrients in preparation for the next winter.
Many birds, mammals, insects, fungi, and bacteria compete with humans for the tender, nourishing stone fruits. The two most serious diseases of all stone fruits are brown rot and perennial cankers.
The brown rot fungus (Monilinia fructicola) infects blossoms in spring, and fruit at harvest time. Symptoms are blighted flowers and twigs, and powdery grey-brown spores erupting from ripening fruit. When rains occur during bloom and near harvest, this disease is a real problem. Removal of all rotten and mummified fruit from the orchard to break the pest's life cycle is the most important control strategy for brown rot. Several fungicides provide effective control if applications are precisely timed.
Perennial canker occurs when injured bark or wood is invaded by certain fungi (Leucostoma and Cytospora) or bacteria (Pseudomonas). The term "canker" actually refers to the symptoms of this disease--festering, oval areas with concentric rings of dying or dead bark tissue on limbs and trunks, and extensive oozing of amber-colored gum. Minimizing injuries such as pruning cuts and freeze injury during the dormant season, and maintaining adequate soil drainage, pH and fertility are essential for canker control.
Black knot (Apiosporina morbosum) can be a real problem on neglected plum trees, but it can be controlled in home plantings by persistent removal of the green/brown swellings on the twigs as soon as they become visible after leaf drop.
Two insects cause the most serious injury to stone fruits--tarnished plant bug (Lygus lineolaris), and plum curculio (Conotrachelus nenuphar). Both attack and disfigure the fruit, causing it to rot, and often drop prematurely. These pests are very difficult to control without insecticides during the post-bloom period. Tarnished plant bugs feed on many plants, especially clovers and other legumes, and they move up into trees causing the most damage during the weeks during and after bloom. Removal of infested fruit from the orchard during the "June Drop" or allowing livestock to eat fallen fruit will help, but major losses are common in unsprayed trees.
Birds, opossums and raccoons love to eat stone fruits, and can steal your whole crop in just a few nights. The most effective control for both pests is wrapping the entire tree in plastic netting. This should be done as soon as the fruit begin to color up and soften, at least several weeks before harvest. The netting must completely enclose the tree canopy, and be secured firmly around the trunk. Netting also protects tree limbs and fruit spurs from breakage and damage by raccoons. If carefully applied and removed, most netting can be reused for many summers.
Peaches, nectarines (which are just fuzzless peaches), and most apricots are fully self-compatible and do not require a genetically different tree to provide pollen. Tart cherries and the European type plums or prunes such as 'Stanley' which are well adapted to New York conditions are partially self-compatible, but will usually set better crops with a different variety blooming nearby.
Almost all sweet cherries are self-incompatible--there must be two different varieties of certain types to provide effective pollen. Fortunately, there are two sweet cherries--'Stella' and 'Lapins'--that can pollinate themselves and all other sweet cherry varieties. There are usually plenty of wild bees, flies, beetles and other insects to transfer pollen among the profuse and colorful blooms of stone fruits.
Training and Pruning
The wood of stone fruits is flexible and often breaks when trees are heavily cropped. This limb breakage can be avoided by spreading branches outward with braces or weights to create a crotch angle around 60° from the vertical trunk.
The best time to do this is during the first several years of tree establishment, so that the whole tree has an open center or vase shaped canopy. This tree form also improves light and air circulation inside the canopy, minimizing brown rot and perennial canker problems.
Unlike other tree fruits, stone fruits can be pruned at petal fall in late spring, ideally during warm dry weather. This late pruning reduces perennial canker infections in pruning cuts, allows you to remove winter-killed branches, and makes it possible to adjust your pruning to compensate for the occurrence of bloom-time frost damage.
Cherries, plums and apricots require relatively little pruning--usually some thinning out of densely clustered inner branches or old damaged branches will be sufficient. Peaches benefit from more drastic pruning, with extensive thinning-out and heading-back cuts to stimulate a flush of new shoots which will set the subsequent summer's crop. This timing allows the trees to heal cuts quickly and resist the canker pathogens.
When pruning any fruit tree, make your cuts parallel to the branch base, close but not into the raised "collar" of bark callus which circles the base of each branch. Try not to damage this callus ridge, because it is where the wood's healing process actually begins.
In years when Nature does not thin your peach crop with a winter deep-freeze or a late frost, it may be necessary to hand thin peaches. When the natural June fruit drop is over, remove enough peaches to leave a hand's breadth between the fruit along each branch--the remaining fruit will be bigger, tastier, and the tree will suffer less branch breakage.
It is usually not necessary to thin the other stone fruits by hand, although plums may occasionally benefit from it in years when there is a heavy fruit set.
To enjoy the fruits of your labor you must know when to pick them. Skin color is not very reliable indicator of ripeness in peaches or plums.
As peaches begin to ripen, the background skin color-its base color beneath the superficial blush--gradually changes from green to yellow or orange. At the same time, the fruit swells rapidly in width, perpendicular to the plane delineated by the two surface ridges along its flanks. The peach develops its full aroma, and softens to the touch. It is usually best to harvest fruit selectively, several times on each tree over a period or a week or more. Once peaches ripen fully they should be picked and used promptly, because they become rather perishable and very susceptible to brown rot.
Plums swell, develop a dusky wax bloom, soften to the touch and sweeten to the taste as they approach ripeness.
Cherries deepen in color, swell and soften, and their sugar content increases rapidly. Both these fruits become susceptible to splitting if rained upon around harvest. Once the skins are split, the fruit must be eaten or processed quickly, before they are invaded by brown rot spores.
Growing stone fruits is a gamble in New York, but many home gardeners consider it worthwhile anyway. They are compact and attractive trees in the landscape. Their profuse blooms of fragrant, colorful flowers are a joy early in spring even if they are nipped later by frost. They will attract birds and other wildlife to your yard, and there is often enough fruit for all to share. Above all, you can't buy the superlative taste and tenderness of a home-grown stone fruit at the supermarket.
Dr. Ian Merwin, Assistant Professor, Fruit and Vegetable Science Department, Cornell University