Master gardener Paul James offers some tips on how to bring overgrown shrubs under control.
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Shrubs are an important part of any landscape, providing structure, texture and color. But all too often they don't get the attention they need. Few shrubs are maintenance-free, and stoloniferous shrubs (those that produce suckers) can become overgrown, tangled and misshapen messes. Master gardener Paul James demonstrates how to maintain a number of choice shrubs, in particular those that sucker.
Virginia sweetspire (Itea virginica), specifically 'Henry's Garnet', has four seasons of interest. But for all its attributes, this USDA Zone 5 native has one drawback. It suckers, meaning that it produces shoots that pop up all over the place, especially when grown in the moist soil it prefers. Unless the suckers are removed routinely, the plant can spread rather rapidly.
However, removing the suckers is as simple as severing the root to which they're attached. You can either cut the root at the base of the sucker or follow it all the way back to the mother plant and cut it there. You can do this anytime, but James prefers to do it during the dormant season because it's easier to see what you're doing when the shrub is bare.
With its bright yellow flowers, forsythia is the colorful harbinger of spring. However, it can also become overgrown as a result of suckering, but it's relatively easy to keep their growth in check. Simply remove the suckers as they appear.
Forsythias also produce volunteers that pop up wherever a weeping branch comes in contact with the ground and takes root. Although not technically suckers, these volunteers can be dug up and planted elsewhere in the landscape or presented to friends as gifts.
While you're at it, it's a good idea to remove the thick, older branches within the interior of the plant. This may require the use of heavy-duty loppers or a bow saw. Doing so will result in a more vigorous shrub.
Ideally, you should dig and replant any volunteers while the plant is still dormant. However, wait until after the plant blooms to prune the interior. Forsythia produces flowers on the previous year's wood, and if you prune them before they flower, you won't enjoy as many blooms as you would have if you hadn't pruned.
Whether you prune before or after the bloom period, don't worry about causing harm to these Zone 4 shrubs because they're extremely rugged and long-lived, up to 60 years.
Oakleaf hydrangea is also stoloniferous, though hardly to the point where it could be considered invasive. However, you can remove the suckers to prevent the plant from getting too wide, and in some cases, you'll get a sucker with enough roots attached to justify planting the sucker somewhere else.
As for pruning oakleaf hydrangeas, or any other type of hydrangea, James offers a piece of advice: don't prune them, unless you need to remove damaged or diseased wood or if you merely need to enhance their appearance. In those cases, pruning is best done in early spring, just as the leaf buds begin to emerge. However, when left alone, these shrubs perform beautifully, assuming they get plenty of shade in the South and aren't stressed by drought.
By the way, oakleaf hydrangea is hardy to Zone 5, but it actually can be grown farther north. Odds are that it will die back to the ground each year. This means it won't flower since blooms are produced on the previous year's growth. But its rootball will often remain healthy, so northern gardeners can still enjoy its spectacular foliage.
Sumacs are another group of plants that produce suckers, but they're also among the easiest to control because the suckers tend to be rather large and easy to spot and remove. There are varieties that grow well in poor soil, practically anywhere in the U.S. and Canada.
Cornus sericea is hardy to Zone 2 and has cultivars that offer red, green or yellow branches. This dogwood shrub does indeed sucker, especially in wet soils, which is why it's often used in mass plantings to stabilize the soil on the banks of streams or ponds. In the landscape, keep an eye on the suckers and remove them routinely to keep plant growth in check.
But there's another type of pruning you should consider as well. These plants need to be heavily pruned, nearly to the ground, every other year or so in order to produce their highly colored bark.
For example, the branch on the bottom is three-year-old wood, and as you can see, its color is beginning to fade. On top is one-year-old wood, which has the bright yellow bark for which this plant is grown, especially to highlight the winter landscape.
Cornus alba 'Siberica', or Siberian dogwood, another Zone 2 beauty, should be treated in a similar fashion. It doesn't sucker, but in order for its striking, red-barked branches to be most pronounced, the branches should be aggressively pruned every other year in early spring.
While on the subject of dogwoods and suckers, remember that dogwood trees often produce suckers at the base of their trunks. These should be removed, preferably in early spring, to force more energy into the canopy of the tree.
Fothergilla doesn't sucker, but they occasionally need a little trim. This fothergilla has produced a strong central leader, a main trunk that makes this shrub look a bit out of balance. Now you could leave it alone and hope that the lateral branches will fill out a bit, but this may not happen. So James recommends removing the central leader all the way to the ground. By doing so, you will force growth back into the other branches so that this shrub will, in time, have a more uniform appearance.