Forsythias and spring flowering shrubs

Posted May 16, 2013 at 10:05 am

by Susanne Howard, guest author

Along with the spring flowering bulbs, nothing says spring to me like the bright big yellow beacon of a forsythia in bloom. They are often accompanied by coral-colored flowering quinces, and followed a little later by white spireas, and again a little later by red or pink weigelas. Many of these large (8-12 feet high and wide) shrubs have been around long enough to be considered heirlooms.

Covered in flowers, their impact is huge. Bees and hummingbirds (for the weigelas) love them. But while they make great backdrops for perennials borders and can divide large gardens like walls into smaller rooms, many gardens just don’t have room for something that big. So some of the newer varieties are dwarf – dwarf forsythias grow two to three feet tall and wide instead of 10 feet or more. Weigelas also come in several sizes from the old-fashioned ones that get 12 feet all around to My Mone or Midnight Wine which get less than two feet tall and wide.

I hope I have convinced you that having a few flowering shrubs is a good thing, but what about maintenance? Too often I see overgrown thickets of one or more shrubs in older gardens, or the hedge-pruned, flat-topped box-pruned shrub. So yes, shrubs do need a little TLC once a year to keep them from taking over and not blooming as well.

Like fruit trees, shrubs bloom best on branches that are not too old, and slightly thinning the shrub encourages air movement through and sunlight penetrating (and allowing flower buds to form) into the shrub. What sets a shrub apart from a tree is that they have lots of small trunks instead of just one big one. Some shrubs can be even be trained into a small tree form by removing all new shoots from the base, like service berries or some viburnums for instance. But mostly you will be faced with a thicket of stems all growing from a small area at the base.

When you buy a shrub, let’s say a forsythia, it will be pretty small. Depending on your soil condition and how much you fertilize, it will not need to be pruned for two or maybe even four years until it develops several large stems and starts to get fairly dense, except perhaps shortening some shoots that grew way out of proportion with the rest of the shrub.

Thinning the forsythia is easy to describe, and possibly a lot harder to actually accomplish. You will need a long handled pruner or a longish, narrow bladed saw. Start by cutting off one or more of the oldest stems as close to the base as you can get. In an older, larger forsythia, where several stems will be taken out, select them so that the upper part of the removed stems are distributed on all sides so that the overall rounded form of the plant is retained. Otherwise you might create holes on one side. Any pruning should be done after flowering. Making cuts will stimulate new growth, on which flower buds for the next year will form.

Thinning will not reduce the overall size of the forsythia. In addition to removing some large stems, you can cut out parts of branches by cutting back to where the branches fork. This can be used to shorten some really long shoots and to shape the forsythia overall a bit, and it can keep the size contained a little, but it will not change an eight foot shrub into a four foot one.

One issue specific to forsythias is that they like to tip layer: wherever a branch rests on the ground and is not occasionally moved about it will root and another forsythia will start right there, and this is one of the reasons why you can see huge forsythia thickets in old gardens.

If you want to avoid this, prune the tips of the lower branches where they fork, removing the lower part of them. This is something that you don’t want to overdo though, I at least believe that a forsythia where all branches hover several inches above the ground like a ballerina skirt looks very odd. To prevent shoots from rooting, simply pull them up if they show signs of rooting, or if that does not work anymore, dig them up. This will also give you a start for a new forsythia to plant elsewhere or to share with a fellow gardener.

Direct comments or questions concerning this column to Marilyn Odneal via email at MarilynOdneal@missouristate.edu; write to Missouri State Fruit Experiment Station, 9740 Red Spring Road, Mountain Grove, Mo. 65711; or call (417) 547-7500. Visit our Web site at http://mtngrv.missouristate.edu.