The amount of light that reaches the ground under a tree, and the kinds of plants you can grow there, depend on how much light penetrates the tree’s canopy. You can open the crown of a tree in a few different ways, depending on the tree, to allow enough light to grow the plants you want.
These are good techniques to help a struggling lawn. Sometimes a little more light makes the difference between a thin, patchy lawn and a lush thick one.
Thinning
Use thinning cuts throughout a tree to create dappled shade beneath it. This pruning technique works best on round-crowned deciduous trees, such as maples, zelkovas, and hawthorns. As you prune, keep your eye on the shade pattern beneath the tree. Remove branches with an eye to letting more light through to the ground. Use thinning cuts to remove whole branches back to a larger limb or at least to one that’s almost the same size as the branch you’re cutting. When you’re through, the tree should look much the same as before you started, but be less dense.
The reduced density will last for two to five years—branches will not regrow within the tree because you used thinning cuts rather than heading cuts. The new growth will be at the exterior of the tree, as if you hadn’t pruned at all.
Vigorous trees like fruitless mulberry may react to a heavy thinning with a burst of watersprout growth the following spring. To avoid this reaction, prune in mid-summer, after the rush of spring growth has slowed. It’s also easier to see the effect of the pruning if the tree is in leaf.
Consider hiring a certified arborist if the tree is large. Working in large trees is difficult and dangerous.
Lifting the Skirts
You can “skirt” a tree whose branches reach almost to the ground by removing some of the lowest branches. If the lowest branches are left at 5 feet high or more, a considerable amount of light will enter under the tree, allowing gardening there, and also opening the area to view so the garden can be enjoyed. The branches on large trees can often be lifted to 10 or 12 feet above the ground.
Skirting doesn’t change the nature of broadleaf trees very much. When you are through, the tree has the same basic character, but the ground underneath is brighter.
Conifers whose lower branches sweep the ground, such as redwoods, spruce, and junipers, are changed dramatically by skirting. These trees have a solid, anchored look when their branches sweep the ground, but appear to float above the landscape after their branches are lifted. This may not be desirable, especially in park-like setting.