Dr. Grow: Pruning for good growth: Timing is essential to keep plants blooming and healthy

In my last column I explained why to prune. Today I am going to discuss when to prune. For a lot of people this is a very complicated subject. Therefore, I am going to start with a general guideline, and then discuss the exceptions to the rule. Maybe this format will make some sense to you.

Most of the time I suggest that if you are going to do some extensive pruning, do it when plants are dormant. Dormancy usually occurs during the winter months. A good rule of thumb suggests that you prune when most of the trees in this area have lost their leaves.

Now, the exceptions to the rule. Elm, birch, and maple bleed heavily when pruned. Because of this tendency, it is best to do extensive pruning on these trees during the summer. Bleeding will be reduced in the summer because the actively growing plants can stop bleeding faster than dormant trees can.

If you are going to remove dead branches, do it during the summer months. If done during the winter, it is hard to tell which branches are alive and which are dead. If done during the summer, a quick glance can tell you which limbs need to be removed.

If you want to maximize flowering, then you need to know whether the tree or shrub blooms on this year's wood or on last year's wood. For example, azaleas, forsythia, and viburnums bloom on last year's wood. If you prune them in the fall or winter, you will be removing bloom buds for next spring. It is best to prune these shrubs right after they bloom, and before they set bloom buds for next spring.

Summer blooming spireas, roses, and crape myrtle bloom on this year's wood. It is best to prune them in late winter before they sprout out in spring.

If you want to prune pines and spruces so that they grow more densely, then prune them in May or June. Limit your pruning to the current year's growth. When shearing current year's candles in May or June, new buds are formed at the end of the cut off twig. In fact, there are generally two times as many buds formed than if no pruning was done at all. These additional buds produce more twigs next year, and consequently the tree is bushier.

If you want to slow plant development and reduce plant size, then prune immediately after the spring flush of growth. By pruning in late spring to mid-summer, leaf area will be minimized for the rest of the growing season. Many people prune yews, boxwoods, and junipers in this manner.

If you find diseased tissue in your trees or shrubs, it should be removed as soon as possible. Sanitation pruning will reduce the spread of disease. For example, fire-blighted tissue in Bradford pear should be removed as soon as it is found.

The foliage of ornamental grasses and liriope should be removed sometime during the winter. Wait until all of the foliage turns brown before removing. If you think that the foliage looks unkempt, remove it late in the fall. If you like to see the foliage sway in the breeze in the winter, then remove the foliage just before new shoots start emerging from the ground.

Foliage of perennials should not be removed until it begins to turn brown. If you remove the foliage before it turns brown, you have eliminated the manufacturing capacity of the plant. Continual early removal of foliage can result in a weakened plant that will eventually die.

As you can see, the rule of thumb for pruning has a lot of exceptions. These exceptions are determined by the why of pruning. In fact a little pruning here or there can be done at any time of the year. Just use common sense and remember that there may be consequences to the timing of pruning.

Paul Schnare of Cape Girardeau has been in the lawn and garden business for more than 20 years. He is an adjunct professor in horticulture at Southeast Missouri State University.