Mulberry trees (Morus spp.) are known for their rapid growth and abundant fruit, but they require timely pruning to maintain a healthy structure, manage their size, and encourage strong fruiting. Pruning is a process of selective removal that improves air circulation and light penetration throughout the canopy. Because these trees have distinct growth cycles, the timing of pruning is important. The tree’s unique biology, especially its tendency to produce a strong sap flow, dictates when major structural cuts can be safely made.
Primary Pruning: The Dormant Season Window
The most appropriate time for conducting major structural pruning on a mulberry tree is during its deepest state of dormancy, which typically occurs in late winter or very early spring. This window generally falls between January and March, after the harshest winter cold has passed but before the buds begin to swell. Pruning at this time minimizes the stress placed on the tree because its metabolic processes are significantly slowed down.
The lack of leaves provides an unobstructed view of the tree’s structure, making it easier to identify problem areas like crossing branches or weak limbs. Large-scale cuts—such as removing deadwood, eliminating rubbing branches, or making significant height reductions—are best reserved for this period. Wounds created during dormancy have the entire upcoming growing season to heal, allowing the tree to direct maximum energy toward callousing. Fewer fungi and bacteria are active in the cold weather, which lowers the risk of infection entering the fresh cuts.
Avoiding Sap Bleeding: When Not to Prune
Mulberry trees are prone to a phenomenon called “bleeding” when pruned at the wrong time. This occurs when the tree’s sap begins to rise vigorously in late winter or early spring in preparation for the growing season. Pruning when the sap is actively flowing causes a continuous, watery exudate to leak from the cut site, resulting in the tree losing valuable sugars and water.
This loss of sap is not immediately fatal, but it can weaken the tree by depleting its energy reserves and making it more susceptible to pests and diseases. Therefore, the period from the first sign of bud break until mid-summer should be avoided for any major pruning. The best practice is to complete all structural pruning well before the initial rush of springtime sap flow. If a large cut must be made when the tree is actively growing, it will likely bleed profusely for days or even weeks.
Managing Growth: Mid-Season Trimming
While structural pruning is reserved for the dormant season, very light trimming can be performed during the active growth period of mid-to-late summer. This summer pruning is intended for maintenance and canopy management, not for shape correction or size reduction. The goal is to make small, corrective cuts to manage the tree’s density and improve the quality of the fruit.
Tasks appropriate for summer include tipping back overly long, vigorous shoots, removing suckers growing from the base, and cutting out water sprouts that grow straight up inside the canopy. These minor trims help increase light penetration and air circulation within the tree, which aids fruit ripening and reduces the risk of fungal issues. However, summer trimming should be minimal, as removing too much foliage during the growing season can stress the tree and reduce its photosynthetic capacity.