Crape myrtles are a Southern favorite. They cannot be grown in the extreme north because of cold, but they love our warm Southern weather. They love it so much that they grow quite vigorously in summer, often requiring pruning the next spring.
Many people think that crape myrtles have to be pruned severely to bloom well. This is not so. Winter pruning of crape myrtles will tend to produce more growth (which can produce more flowers), but pruning is not required for bloom. You need to decide whether to prune your crape myrtles and how heavily to do so based on what you want them to look like and how big you want them to grow.
Crape myrtles are durable plants. They usually grow back no matter how we prune them. However, the method of pruning we select will determine the ultimate size and shape of the crape myrtle and how well it will bloom.
There are several pruning methods. Select a method based on the type of crape myrtle you have. Most crape myrtle varieties are trees. A few smaller types are meant to be shrubs. Pruning the shrub-type crape myrtles is relatively easy. Shape them as you would other shrubs. Remove some interior branches when the shrubs get too thick.
Most crape myrtles are tree-form. They produce small trees anywhere from 5 to 25 feet in height. The ultimate height is based on the variety you select and the way you prune.
Tree-form crape myrtles can be pruned in several ways. Many people merely cut all the branches at one level. I call this pollarding or giving them a haircut. This method is usually less work, but the trees form is severely affected over time. Pruning like this every year creates a knot of small branches at the point of pruning. The tree is stunted over time and cannot grow into a proper tree form. The resulting plant looks like a blooming umbrella in summer. If pollard pruning is done too vigorously, the plant may slow growth or die.
Pencil pruning may be a better method of pruning crape myrtles for many gardeners. Pencil pruning allows the crape myrtle to grow into a natural tree shape. Each tree may have one to three or more main trunks. Pencil pruning consists of first removing any un-wanted sprouts or suckers at the base of the plant. Then, remove all growth in the top of the tree that is smaller in diameter than a pencil. This will remove last years seed heads as well. Remove any broken branches or branches that cross over one another.
The third method of pruning tree-form crape myrtles is to not prune them at all. Unpruned plants will form a small tree with numerous branches.
Pruning affects flowering. Unpruned crape myrtles often have smaller flowers but should have more of them. The flowers will be scattered throughout the tree. Pencil pruned trees will probably have larger flowers but fewer flowers than unpruned plants. The flowers will be scattered throughout the tree. Pollarded trees usually have fewer but larger flowers (like the pencil-pruned trees), but the flowers are usually arranged all at one level around the tree. During bloom the large flowers make the branches bend over, and the plant takes on an umbrella shape.
Some gardeners want to change their pollard-pruned trees by removing the knots formed by cutting the limbs at the same level each year. To do this, cut below the knots. When the tree branches out in the spring, remove all the new growth on each stem except one to two outward-pointing branches. Select strong, healthy branches and allow them to grow larger every year. Prune these branches lightly using the pencil pruning method. Remove other branches that grow from the main limbs, leaving only the branches you selected.
Just as a reminder: Crape myrtles need a full sun location. They grow best with regular watering but do not like to be watered too often. Water them deeply once a week during drought. Winter is a good time to plant crape myrtles, but select powdery mildew-resistant varieties. For more information, see http://tinyurl.com/ajcugwk.
Willie Chance works with the University of Georgia Center for Urban Agriculture and helps to train the turf and landscape industry.