Home gardeners are often intimidated by the prospect of caring for tree fruits, which come with a long list of potential insect and disease problems. Growing healthy cherries holistically, however, allows the gardener to avoid using synthetic chemicals. It begins with understanding the ways of trees.
The holistic approach to growing fruit involves enhancing the tree’s immune response and surrounding it in a competitive microbial environment—one in which beneficial species of bacteria and other microbes outcompete the pathogenic, or disease-causing, microbes. Holistic actions integrate plant and soil health into a self-sustaining system; plants stay naturally healthy and are better able to ward off pests and diseases. The undesirable alternative to holistic methods is to use harsher medicines—fungicides and pesticides—to counteract biological and nutritional deficiencies whose symptoms show up as insect pests and assorted diseases. Everything in nature is interdependent...including robust cherry health!
Few of us live where both sweet and sour cherries thrive, to be honest. Sweet cherries love an extended growing season on the dry side, and their blossoms are more vulnerable to late spring frosts. They are best suited to USDA Plant Hardiness Zones 6 to 8.
Sour cherries, on the other hand, prefer cool summers and cold winters. They have innate hardiness down to –40°F—thus giving northern growers a legitimate shot at a piece of the pie. The hardiest varieties of sour cherry will crop in Zone 3, with all varieties suited for Zones 4 to 6.
The challenges stack up when you push either type further. The coldest winter temperature that sweet cherry blossoms might survive is –20°F, which sets a nonnegotiable limit on sweet cherry production as you head north. Sour cherries will be of respectable quality farther south if they are grown at higher elevations where spring weather is cooler. Your county Cooperative Extension office can recommend the types of cherries that are best suited to your region.
All cherries thrive in soils that are well drained, yet retain moisture. Cherries do not adapt well to heavy clay. Plant them on higher ground (locally speaking) wherever possible.
Sweet and Sour Varieties
Sweet cherries are firm, dark, and luscious. Soft-fleshed ones often come in paler shades. Sweet cherries are generally not self-fertile, so cross-pollination dynamics come into play. Select two varieties with compatible bloom times to ensure a bountiful harvest. ‘Black Gold’, ‘Hedelfingen’, ‘Kristin’, ‘Rainier’, and ‘Stella’ are good choices.
Don’t be fooled by the word sour in considering pie cherries. Tree-ripened sweetness backed with puckery attitude doesn’t mean these are any less delectable for eating fresh off the tree. And then there are those latticed pies and crumbly crisps in which the fruit’s bright tang is tamed with sugar. Sour cherries also make the best dried cherries. One tree alone will make a crop, as all varieties are self-fertile. Consider ‘Danube’, ‘Evans’, ‘Meteor’, and ‘Surefire’ for starters.
|Click for larger cherry images|
|'English Morello'*||'Hedelfingen'||'Lambert'||'Napoleon'||'North Star'*||'Rainier'||'Stella'|
|* indicated a sour cherry|
Photography by Mathew Benson; Roger Stowell; Andrea Jones; Garden World Images; Age Fotostock; Photocuisine; Rob Cardillo Photography; Agstock Images Inc.; John Glover.
Tree Size and Spacing
Whatever variety you select, it will likely be grafted to a rootstock that determines its vigor and thus tree size. Sour cherries on seedling rootstock mature at a manageable 10 to 14 feet high, but sweets can reach 40 feet or more. Mahaleb rootstock, the standard choice for sour cherries, requires well-drained soil. Mazzard rootstock, propagated from the seed of a wild sweet cherry, tolerates wet ground but bites the dust if the thermometer drops much below 0°F. Backyard growers should consider dwarfing rootstocks, like the Gisela series from Germany.
Space sour cherries 8 to 12 feet apart. Sweet cherry trees on standard rootstocks need to be 30 to 35 feet apart, with dwarfs spaced as little as 6 to 10 feet apart. Keep soil around young trees free of turf and weeds for the first few years. A uniform ring of mulch benefits trees in these wood-growing years.
Pruning for Continuous Production
In the development years, encourage strong scaffold branches by pruning away those that are crowded or weak. Once fruiting begins, pruning consists mainly of thinning growth each year to allow sunlight to filter into the canopy. A tendency toward stoutness in cherries makes for less whippy growth overall in the tree’s upper reaches.
Cherry wood has a tendency to “go blind”—cease producing flowers and fruit—rather quickly. Buds that flower one season no longer are in the game, so to speak, pushing the productive zone further and further out from the trunk. Pruning cuts made into 3-year-old wood can stimulate the growth of productive stems from older limbs.
The Importance of Fungi
Important allies for fruit trees include the fungi found in a living soil. Mycorrhizal species of fungi form a symbiotic relationship with the trees’ feeder roots, delivering balanced mineral nutrition in exchange for carbon-rich sugars. To make sure this fungal connection is present, sprinkle a commercial mycorrhizal inoculant directly on the tree roots at planting or stir it into the soil in the root zone.
Trees depend equally on saprophytic fungi to break down soil organic matter and thus make nutrients available. Create a “fungal duff” beneath fruit trees by mulching haphazardly with deciduous wood chips, made from brush and branch ends, where a greater proportion of mineral-rich bark will be found. A valuable component of this mulch layer are prunings from assorted hardwood species—including your cherry trees—snipped to short lengths to lie flat. Rake leaves inward each fall and cover with a smattering of compost, as well. All this matches the ecology found on the forest edge, leading to exactly the right kind of fungal presence necessary for tree health.
Photography by Woodystock; Flowerphotos.
Competitive Colonization to Thwart Disease
Not all fungi are good. Pathogenic fungi are behind many cherry diseases, including brown rot, black knot, and cherry leaf spot. This is where the concept of competitive colonization comes into play. Benign bacteria and fungi that live on the aboveground surfaces of the tree are integral to crowding out disease organisms. A holistic orchardist supports these microscopic partners with a spray that combines foliar nutrition with biological reinforcements, affording trees a far better ability to stand up to pathogens. Here the holistic approach totally breaks from strategies that involve fungicides, and frankly is more fun.
The holistic spray recipe consists of unpasteurized liquid fish, pure neem oil, seaweed extract, and a probiotic microbe formulation, all mixed together in a backpack sprayer. Raw milk can be added to the mix for brown rot as cherries ripen. Rates, nuance, and sources for the spray ingredients can be found on the community orcharding website, Grow Organic Apples.
This mixture is sprayed onto leaves and fruits alike at regular intervals to help prevent disease. Time applications to straddle the disease-infection window by spraying at bud swell, just before flowers open, petal fall, and a week after petal fall. The earliest sprays target buds, bark crevices, and fallen leaves on the ground—precisely where many pathogens lie in waiting—with fatty acids from the fish and neem oils. Growers in more humid locations should carry this effort further into the season to prevent brown rot from moving onto fruit as it ripens. Remove all visible black knot lesions to limit further spread of that particular affliction.
Bacterial canker can kill limbs prematurely. The solution here is to not prune during the dormant season in regions where winter tends to be rainy, but rather after the harvest in late summer. Copper applications in earliest spring are organically acceptable for canker, but keep in mind that copper residues reduce fruit set on treated trees.
Biodiversity Helps Check Pests
The holistic approach applies to pests, as well. Cherry fruit flies will get caught up on yellow sticky cards. The latest scourge, spotted wing drosophila, can be checked with an organic formulation of spinosad. All species of moths drawn to cherry trees will be impacted by the neem in holistic sprays. Birds are often the most impactful pest, calling for a serious netting effort to protect the harvest.
What really counts on the pest front, however, is outrageous biodiversity. The more flowering plants a garden includes, the more nectaries there will be to support all sorts of beneficial insects, which in turn seek out pest larvae. A mulberry tree down the block may even keep the birds happy. Put that lawn mower away and let nature grow.
Pest and disease problems are frustrating when you’ve worked so hard to plant, water, and cultivate, only to see moths gain the upper hand or rot ruin nearly every cherry in a particularly wet summer. In a sense, pests and diseases in the orchard should be thought of as symptoms resulting when growing conditions are less than optimal. Natural defense mechanisms abound in a holistic orchard. Our foremost job as growers, starting the very day we plant those precious saplings, is to support the home team.
Photography by William Reavell; Matthew Benson.
Originally published in Organic Gardening magazine, June/July 2014