Advice
RHS Help & Advice
Bleeding from pruning cuts
Bleeding
from pruning wounds, although unsightly, is not always harmful
to plants. There may be some loss of sugars, and in severe
cases it may delay wound healing, but there are no practical
measures to stem the flow of sap.
Bleeding occurs due to the pressure of sap within the water conductive tissues - usually in late winter to early spring. Wounds on larger deciduous trees, such as birch (Betula) and walnut (Juglans) can bleed heavily when pruned at this time.
Trees prone to bleeding are best pruned from mid-summer, when the leaves are fully developed and the spring flush of growth has finished, to before mid-winter when sap begins to rise again. However, Japanese maples (Acer japonicum, A. palmatum) are best pruned after leaf fall but before January, although small cuts can be also be made in late summer and early autumn. Snakebark maples are pruned in late summer.
The timing and individual requirements of each tree should be checked in a pruning guide such as the RHS Pruning and Training Manual.
Trees prone to bleeding include: Acer, Betula, Carpinus, Carya, Juglans, Laburnum, spring-flowering deciduous Magnolia, Morus, Populus (some species), Sophora, Tilia and Vitis (grape vines).
More information
Pruning acers
Pruning magnolias
Pruning grape vines