December 2013 Cuttings

"Cuttings" is your source for garden updates and horticultural tips from Reeves-Reed Arboretum's horticulture staff. Check back monthly to find out what's blooming at the Arboretum, get the inside scoop on upcoming events, and learn some timely tips you can put to use in your own garden.

To Prune or Not To Prune?

Even though we've been enjoying a mild autumn and early winter, things are still going full speed ahead in the garden. As long as the temps stay warmish and there isn't snow falling, there is still plenty to do in the garden.

Now that the leaves have finished falling and the bones of the garden are seen in stark contrast to the leafy summer, it's a good time to get out there and prune away! Most of the trees, shrubs, and perennials – not to mention pests that can affect them – have settled down for their long winter's nap so there's less of a chance of causing injury to the plant that you're pruning. In fact, now is the perfect time to give your small trees and shrubs a good shaping up. But where to start? My gardening mentor in England said it best: "You have to start somewhere".

A thorough discussion of how and when to prune dead or diseased limbs was covered in last year's December Cuttings, so I won't repeat that here. The pruning we've been focusing on this winter is to remove suckers and any broken branches left over from recent storms. Suckers can be caused by a break or cut during the growing season when latent buds jump to life in an effort to replace the branch that was removed but instead of one branch there are several growing from a single point. They can also shoot up from the base of the plant, in which case they are known as root suckers. In the wild, this isn't necessarily a bad trait for a plant to have since it helps a plant that is in peril survive and reproduce. In cultivation suckering can help us in propagating more of a desirable plant, but they can be unhealthy for the plant, and are usually unsightly.

I'm not sure how these vigorous growths got the name 'suckers' but my theory is that it's because they suck the life out of the plant. Also called 'basal shoot', 'root sprout', 'adventitious shoot', or 'water sprout', they are easy to identify by their rapid upward growth and longer internodes (the space between buds). Suckers rob energy from the main plant and can result in a weaker plant overall.

The root suckers on this Saucer Magnolia (Magnolia soulangiana) are obvious and not terribly attractive, obscuring the shape of the trunk. Cutting them off at the base will not only tidy up the tree, but will allow us to see its structure better. Removing these growths will also allow the main tree to use its energy more efficiently. If allowed to remain, these suckers would grow too large and would eventually take over, to the detriment of the main plant.

These two suckers on our Japanese Cherry (Prunus serrulata) are a lighter color than the other branches, and the spaces between buds are further apart. Notice how they're both growing straight up from the same point? If they were allowed to continue growing they would not only crowd each other, potentially causing wounds in the bark which would allow pests and disease to enter and infect the tree, they could become too heavy for the branch to bear and the whole thing could break. Bad news either way, so they need to go.

On this Flowering Dogwood (Cornus florida), the suckers caused by the branch breaking are clearly seen. Notice how the suckers are growing straight up even though the branch curves downward. You can tell where the branch broke, and even though it is still alive and will flower, the wound created by the break is large and the entire branch is compromised. A strong wind or heavy snowfall could cause it to snap off completely, not to mention the break creates a welcome mat for any pest and disease organisms that might happen by. The extra weight created by the suckers, if allowed to remain, and energy they use would only contribute to the tree's further demise. The best course of action is to prune the entire branch below the breaking point, creating a clean cut that will heal quickly. Pruning to an outward facing bud could also encourage the growth of a new branch to compensate for the one that is removed and help retain balance in the canopy of the tree.

This type of pruning is simple on small trees and shrubs (think of the suckers on your lilacs or roses!) but where suckers are sprouting from branches high up, it's best to hire a professional. They have the right equipment and training to be able to prune in a way that will enhance the health and aesthetics of the plant, which can affect the entire landscape.

One added benefit of this kind of pruning at this time of year: some of the dogwoods and magnolias already have flower buds on them. If you prune them and put the cuttings in water and set them in a warm, sunny spot, the buds will break and you'll have flowering branches to add to your winter décor.