When to Prune

     We are heading into the '60's in Chicago this week, so I am jumping ahead of myself for those impatient to DO SOMETHING. The quick answer to the question of when to prune is "now." I have been pruning since the last week in February -- behind your back.


     We are in what the gardening books call the "late dormant period." In our climate zone most of our plants simply hibernate during the winter and wait for better times. Their vascular systems are shut down. Therefore when they are cut they do not "bleed." This is one advantage of pruning in the dormant season. Another is that the absence of foliage makes it easier for you to see what you are doing. Pruning in late winter also lets you cut out any winter damage that may have occurred. 


     But the biggest advantage of pruning about now is that we are performing our surgery just before our patients throw a huge amount of stored energy into a growth spurt. By doing our cutting now we make sure that our plants recover quickly and we also make sure that all the new growth is directed where we want it, not into leaves and branches that we are going to cut off later.


    Simple, right? But now, just like in grammar school, we no sooner learn a rule than we are told there are "exceptions." Wonderful! These are not as terrifying as many think, however. Most of them have to do with flowering, so if you goof up the worst thing that will happen is that you will lose your blooms for one season.


     The books make a distinction between "new wood" and "old wood." Many plants produce new flower buds at the same time they are growing new stems and leaves. These are "new wood" plants that can be pruned now because they have not started to produce their buds.


     The exceptions are those plants that produce their buds on last year's growth. The buds lie dormant during the winter and won't open until later this spring.The most popular of these "old wood" are forsythia and lilacs. If you prune these plants now, you will cut off their flower buds from last year and the new buds will not flower until 2013. This is not the end of the world, but it is pretty annoying if you planted them for their flowers. These old wood plants should be pruned once immediately after their bloom has faded and then left alone.

     You can make a good guess about which type of plant you have based on bloom time. Spring bloomers tend to be flowering on "old wood." Summer and fall bloomers are more likely to be based on "new wood." Logical, right? The tricky ones are hydrangea and clematis. Different species are either "new" or "old" wood plants, and the very-popular 'Endless Summer' hydrangea blooms on both.


     The Internet has made sorting through this confusion much easier than it used to be. If you know your plant's name, you can type in something like "pruning Mock Orange" to find out if it is a new or old wood plant. But even if you don't know what you have, you will do all right if you remember these three things: 1) Stay away from forsythia and lilacs. 2) Suspect spring bloomers to be "old wood" plants. 3) Be cautious with hydrangea and clematis if you can't find out which they are. Go ahead and make some snips but don't bet the farm on this year's pruning. You can always prune more next spring.


     Remember that all these rules are not matters of life and death. They are simply strategies for maximizing the effects of your labor. Nature "prunes" all year long via animals, falling tree limbs, hails storms and more. You can not really do serious damage to your plants by pruning at the wrong time. You can do a lot more damage by pruning in the wrong way. More on that later.