Winter is a crucial period for plum trees, influencing their health and productivity. During these colder months, trees undergo physiological changes requiring specific care for resilience. Understanding their unique winter needs maintains vigor and prepares them for successful fruit production, establishing a strong foundation for the annual cycle.
Plum Tree Dormancy
Plum trees enter dormancy as temperatures drop and daylight shortens; this critical survival mechanism conserves energy and protects the tree from harsh winter conditions. During dormancy, metabolic activity slows, and visible growth ceases, preparing the tree for spring. Sufficient “chill hours” (cold temperatures, typically 32-45°F or 0-7°C) are necessary for plum trees to break dormancy and flower productively. Most varieties require 700-1,000 chill hours for optimal bud development and fruit set, though some Japanese plums need less. The tree undergoes internal biochemical changes, like carbohydrate storage and flower and leaf primordia development, essential for future fruit production.
General Winter Care
Proper soil moisture is important for plum trees in winter, especially in dry regions. Dormant trees still need water; if precipitation is low, deep water every few weeks, particularly before a hard freeze, prevents root desiccation and keeps the tree hydrated. Dry soil freezes deeper, so keep soil consistently moist but not waterlogged. Applying a 3-4 inch layer of organic mulch (wood chips, shredded bark, or straw) around the tree’s base provides significant winter benefits, insulating roots from temperature fluctuations and reducing frost heave. Extend mulch to the drip line, keeping it a few inches from the trunk to prevent rodent damage or moisture buildup; it also retains soil moisture and contributes organic matter, improving soil health.
Dormant Pruning
Dormant pruning, from mid-to-late winter before bud break, promotes plum tree health and fruit production. This timing minimizes stress and disease risk, as pathogens are less active and the tree’s energy focuses on healing. Primary goals include shaping the tree for a strong scaffold structure, improving air circulation within the canopy, and removing dead, diseased, or crossing branches. Proper air circulation reduces fungal diseases by allowing foliage to dry quickly. Use clean, sharp shears, loppers, or a pruning saw. Sanitize tools between cuts, especially for diseased wood, to prevent pathogen spread.
Types of Cuts
Thinning cuts remove entire branches back to their origin to open up the canopy and allow more light penetration.
Heading cuts shorten branches to encourage bushier growth or to manage tree size and height.
Remove suckers (shoots from rootstock/base) and water sprouts (vertical shoots from main branches) as they divert energy. Always cut just outside the branch collar for proper wound healing and to minimize disease entry. Wear protective eyewear and gloves.
Winter Protection
Protecting plum trees from winter damage is important, especially for young or newly planted trees.
Common Winter Damages and Protection
Frost Damage: Occurs when temperatures drop rapidly, freezing plant cells. Cover young trees with a blanket, burlap, or tree cover before a hard freeze. Secure the cover to trap warmth, but remove it during warmer daytime periods for air circulation.
Sunscald: Characterized by cracked or peeling bark, often on the southwest side. It results from bark warming significantly on sunny winter days and rapidly cooling at night, causing cell damage. Apply a white tree wrap or paint the trunk with 50% diluted white latex paint to reflect sunlight and prevent temperature fluctuations.
Animal Damage: Rabbits, voles, and mice can gnaw on bark, girdling the tree and potentially killing it. Install wire mesh tree guards (18-24 inches high, buried slightly below soil line) around the trunk. For deer, consider repellents or taller fencing in high-population areas.
Pests and Diseases in Winter
Winter is an opportune time to inspect plum trees for overwintering pests and diseases, allowing for proactive management. Look for aphid eggs, scale insects, unusual growths, discolored bark, or cankers (sunken lesions often associated with fungal or bacterial infections). Cankers can harbor pathogens active in warmer weather.
General sanitation is important during dormancy. Clear fallen leaves, mummified fruits, and other plant debris from around the tree’s base. This reduces sites where fungal spores or insect eggs can overwinter and prevents them from serving as an inoculum source for diseases like brown rot or peach leaf curl in spring.
For overwintering insect pests, a dormant oil spray is an effective control. These horticultural oils suffocate insect eggs and larvae on the bark. Apply dormant oil when temperatures are above freezing (40-70°F or 4-21°C) and no freezing temperatures are expected within 24-48 hours.