Making the cut

It’s time for the pre-Christmas prune, says Toby, as he looks at why some trees ‘bleed’ when they’re cut

- Toby Buckland

WITH Yule around the corner, it’s time to get organised – and I’m not talking about making a list for Santa. ’Tis the season to be sawing and sharpening secateurs in readiness for the pre-Christmas prune.

Deciduous plants have dropped into complete dormancy and that makes the advent of er, Advent, the least stressful time to prune the ‘bleeders’ – trees that weep sap when cut. These include birch, magnolia, maple and grapevines in my own garden, plus the mulberry, poplar, tilia, laburnum, walnut and hornbeam I wish I had space for.

The reason these trees bleed is down to their deciduous physiology and the fact that their roots absorb water even after the leaves have fallen. This water mixes with minerals to create sap, which is pushed, under a pressure, up into the branches.

Just before bud-break in late winter, the pressure inside the ‘bleeders’ is huge and it’s why cutting causes the wounds to weep excessively. If punctured at this time, their sap floods out like living water balloons.