Q: We have a long row of viburnum along our driveway. They are crowding out other plants and overtaking the lights along the driveway. This summer, for the...
Q: We have a long row of viburnum along our driveway. They are crowding out other plants and overtaking the lights along the driveway. This summer, for the first time, a number of branches died. We have an automatic sprinkler system, but I wonder how much water actually makes it past the leaves to the roots. Should we trim back the plants, and if so, how far? Do you have any idea why some branches died?
A: It was so dry for so long this summer — hard to remember now, after the wettest November ever — that many well-established plants suffered. If your viburnum are too crowded and the sprinklers didn't deliver water to the roots where it was needed, it's no wonder you had some die back.
It sounds like maybe your viburnum were planted too closely together; it might be best to remove every third shrub or so. This way the remaining viburnum can grow to their natural size and shape. Go ahead and prune viburnum anytime, starting with dead or crossing branches.
While you're in there pruning, check to make sure your sprinklers are working well, and that the water is getting to the plants' roots. If not, you might want to add a soaker hose.
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And it wouldn't hurt to refresh the soil next spring with a top-dressing of well-composted manure, which will also help keep the viburnum from drying out.
Q: I wonder if you could give me some advice on selecting a maple tree for the front of our home. We are looking for something graceful around 15-20 feet that would have a nice soft shape. Also, fall color is important.
A: If I could have only one kind of small maple, I'd choose our native vine maple (Acer circinatum) for easy care, lovely shape and glorious fall color. Look for a multi-trunked specimen to lend winter presence to your garden; the cultivar 'Monroe' has especially pretty, deeply cut leaves.
The coral bark maple is another showy small maple, with bright trunk and twigs that stand out in the winter landscape. It has pale green, delicate foliage in summer, but its golden fall color doesn't rival that of the vine maple's fireworks.
Q: I planted two purple wisterias on the west side of my home six years ago. The plants have matured well, climbing up our porch posts and under the eaves. Soil drainage is good, but they do not get a lot of natural water. In the past six years, they've only generated a couple flowers.
I'm watching our neighbors' newly planted wisterias bloom twice a year and in abundance. To say the least, I have "wisteria envy" and am about ready to give up. Any suggestions?
A: A recipe for kicking your vine into bloom:
Two-step pruning: Those leafy summer shoots need to be severely pruned so your plant will put its energy into producing flowers. Prune hard in August, cutting the leafy shoots back to 6-9 inches; then in late winter the previously pruned new shoots should be pruned back to the second or third bud to encourage them to become flowering spurs.
Root pruning: You can jolt a reluctant wisteria into flowering by root pruning in early spring. Drive a sharp spade vertically into the soil around the wisteria in a circle about 2 feet away from the main stem.
Fertilizer: Make sure your plant doesn't get any high-nitrogen fertilizer from the surrounding lawn, which encourages leaf rather than flower. In spring, feed it lightly with a superphosphate fertilizer.
Water: Make sure your wisteria is adequately watered during summer drought.
Valerie Easton also writes about Plant Life in Sunday's Pacific Northwest Magazine. Write to her at P.O. Box 70, Seattle, WA 98111 or e-mail firstname.lastname@example.org with your questions. Sorry, no personal replies.