Jane A. of Windsor asks: What's the best way to prune crape myrtles? Shrub form and trees?
Crape myrtle cultivars are available in a variety of colors, with sizes ranging from a few feet tall to 25 feet. Most pruning problems occur when a plant is planted in the wrong place. If a multi-trunked shrub is planted in an area there there's only room for a tree, moving it makes more sense than having to do excessive pruning (butchering) to the plant every year.
Pruning that preserves the natural shape of any plant, while still controlling the size and shape, is always the best practice. But with crape myrtles, there seems to be this misguided notion that pruning the top out of the tree is the way to prune.
Not so. This “crape murder” only results in oddly shaped plants with oversized, weakly attached, floppy blooms that weigh the spindly new shoots down, producing an umbrella-shaped plant.
The natural look is more desirable for crape myrtles because it allows the plant's beautiful bark to become more exposed, which is a feature of older, more established plants.
Since crape myrtles bloom on new wood, pruning should be done in winter or early spring. With young, multi-trunked plants that have spindly shoots, prune back the plant to about 4-6 inches to the ground. A cluster of new shoots will appear in the spring. Select the shoots you want to grow and prune out the others as they start to grow.
In older, more established crape myrtles, only light pruning is needed to remove the seedpods from last summer and any spindly, twiggy growth. If your crape myrtle is getting too large, it can be pruned back about 20 percent of its height by selective pruning.
Cut branches back to a fork on the main branch. When selecting a side branch to take over as a new growing point, choose one that's at least half the diameter of the main stem to which it's attached. Remove suckers and limbs growing from the main trunks as needed to sculpt the plant into a kind of living artwork.