Pruning a plum tree is necessary to manage its size, improve fruit quality and quantity, and maintain a strong structural framework. This practice directs the tree’s energy, ensuring light and air reach all parts of the canopy. Understanding the specific needs of plum trees in the California climate allows for targeted cuts that encourage a productive and healthy life.
Optimal Pruning Timing for California Plums
Structural pruning should occur during the dormant season, typically in late winter (January and early February in California), just before bud break occurs. Pruning at this time promotes vigorous new growth, which is desirable for developing a strong canopy structure and maximizing next season’s fruit production. Wait until the coldest part of winter has passed but before the tree awakens from dormancy.
Stone fruits, including plums, are susceptible to diseases like Bacterial Canker, which can enter through fresh pruning wounds. Avoid pruning during periods of heavy rain or prolonged cool, wet weather. Pruning only when the forecast predicts at least two days of dry conditions allows cuts to dry and close quickly, significantly reducing the risk of pathogen entry.
Supplement dormant pruning with summer pruning, usually performed in June or July after the spring growth flush has matured. Summer pruning manages the tree’s size and controls excessive vegetative vigor without stimulating new growth. This technique helps keep the tree height manageable for easy harvesting and ensures sunlight penetrates the lower branches.
Essential Tools and Sanitation
Preparation requires gathering the right equipment to ensure clean, efficient cuts that promote rapid healing. Use sharp bypass hand pruners for smaller branches up to a half-inch in diameter. Branches between one and two inches thick require long-handled loppers, and a folding pruning saw should be used for branches larger than two inches.
Sharp blades are necessary because a clean cut heals much faster than a ragged wound left by dull tools. Sanitize tools before starting, and especially when moving between trees or cutting out diseased wood, to prevent the spread of pathogens. Use a solution of 70% denatured alcohol or a 10% bleach-to-water mixture to wipe the blades down between cuts.
Shaping and Maintenance Techniques
The training system chosen for a young plum tree determines its future structure and productivity. Plums are commonly trained to either a Modified Central Leader or an Open Vase system. The Open Vase system removes the main central leader early to encourage three to five scaffold branches to grow outward, creating a bowl shape that maximizes light penetration and air flow.
The Modified Central Leader system maintains a central trunk but limits its height by periodically heading it back, establishing scaffold branches in tiers. This method creates a sturdier, slightly taller, and more naturally shaped tree compared to the Open Vase. For mature trees, maintenance focuses on removing wood that is dead, diseased, or damaged (the three D’s). Also eliminate any branches that are crossing or rubbing against each other, as this friction creates wounds vulnerable to infection.
Structural cuts are categorized as either thinning or heading cuts. A thinning cut removes an entire branch back to its point of origin, opening the canopy for better air circulation and light. A heading cut shortens a branch just above a bud or lateral branch, which encourages the remaining bud to grow vigorously. Remove all vertical, fast-growing, non-fruiting shoots (water sprouts), as well as suckers that emerge from the rootstock below the graft union, as these compete for nutrients.
Immediate Post-Pruning Health Measures
Once pruning is complete, focus on ensuring the cuts heal quickly without complications. Applying wound dressings or pruning paint is not recommended for routine cuts on plum trees. These materials can impede the tree’s natural healing process and may trap moisture that encourages fungal or bacterial pathogens.
The best wound care involves making a clean, proper cut at the branch collar, allowing the tree to naturally compartmentalize the wound. This biological process creates a protective barrier of callus tissue around the injury. After pruning, gather and dispose of all removed wood, especially diseased material, to prevent pests and fungal spores from harboring nearby.
Monitor fresh cuts and the bark for signs of stress or infection, such as the excessive oozing of amber-colored sap, a condition known as gummosis. While gummosis is a natural reaction to stress, it can also indicate a canker infection, which appears as a sunken, discolored lesion on the bark. If these symptoms are observed, a subsequent, targeted pruning cut to remove the infected wood during the dry summer months may be necessary to halt disease spread.