They're Made for the Shade

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By Scott Aker
Special to The Washington Post
Thursday, November 13, 2008

Q Can you recommend some attractive, long-flowering shrubs for our shaded back yard?

A If you want something evergreen, consider Japanese aucuba, Japanese plumyew or leucothoe. Flowers are going to be hard to come by in deep shade, but you might have a shot with one of the hardy gardenias. Chuck Hayes is an upright cultivar; Kleim's Hardy is much shorter and grows to about 18 inches in height.

I plan to create a vegetable garden framed with pressure-treated lumber. I am worried about the chemicals in the wood making their way into the soil and the vegetables. Is this a valid concern?

Pressure-treated wood will not create a toxicity problem in the surrounding soil unless the soil pH is extreme. At normal pH levels, the metals that are used to treat the wood are tightly bound to soil particles and cannot easily be taken up by the roots. It is likely that you will have to bring in topsoil to fill the bed. It is unlikely that the pH of the imported soil will be extremely acidic or alkaline. For peace of mind, you could get your soil tested. Your local county extension agent can tell you how to arrange that.

Avoid wood that has been freshly treated with creosote, which gives off harmful hydrocarbon fumes. Old railroad ties are safe to use, however, because the volatile portion of the creosote has already evaporated.

I have 14 antique roses, variety Belinda. In recent years, borers have become increasingly destructive. We have sealed cuts with glue to keep them out, we have removed canes below the borer infestations and we have used various chemicals. The plants, and the borers, remain vigorous, but the bushes are diminished by the loss of canes.

I have been unable to get any information on the life cycle and treatment of this pest. Can you help?

You've taken the correct control measures by sealing all pruning cuts and by removing damaged canes. If the plants are healthy and you are watering and fertilizing them adequately, they should respond with vigorous new growth that will replace any canes that are lost.

The reason you could not find information about the rose cane borer's life history is that entomologists have not studied it. Another reason is that there are several insects that can bore into rose canes. At any rate, since they feed inside the canes, it is very difficult to control them with any pesticides.

Scott Aker is a horticulturist at the U.S. National Arboretum.


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