Last week we looked a recently-repotted Japanese maple. Kathy and I reduced the roots aggressively, and it leafed out shortly after, as normal.
My analogy of a tree’s energy is like air in a balloon; in the spring, all the energy is squeezed from roots up into the buds, which open, developing into leaves that generate energy, which is squeezed down the trunk and back into the roots where it is stored for the winter.
This is why it’s important to conduct repotting and pruning just after the energy stores in the roots are squeezed up into the shoots and the tree is beginning to form leaves that can generate energy to strengthen the just-pruned roots. All the while, we must be careful to leave enough roots intact to supply the transpiring leaves with water. Got it? Good. Back to the maple.
We reduced the roots by 75% or more, but the tree is heavily ramified. When the buds grow, the tree suddenly has a large amount of surface area transpiring moisture, and relatively few roots to replenish the moisture lost from the hundreds of leaves.
The timing was just right, the energy had definitely been squeezed up into the buds, and the tree didn’t miss a beat leafing out, but did miss the roots needed to support the new growth. The roots couldn’t supply moisture fast enough to the leaves, and they wilted.
The solution? Stay observant, move the tree to mostly shade, out of any wind, and soak the tree several times a day; leaves, trunk, roots and all. It stalled out for a week or so, but soon the leaves were able to produce enough energy for the tree to begin growing new roots, until the tree was back in balance, with roots supplying enough moisture to support the foliage.