Digging In: Advice on Plants Deer Won't Eat, Crape Myrtle, Arsenic in Soil

By Scott Aker
Special to The Washington Post
Thursday, August 20, 2009

Q: Can you recommend plants that deer won't eat?

A: There are many plants deer don't like. Most of them are poisonous. Others have prickles, thorns or fuzzy leaves that make them difficult to eat.

Hellebores, monkshood, daffodils and foxglove have toxic foliage. Achillea and lamb's ear have furry leaves, and hollies have prickles that discourage deer browsing.

However, deer will attempt to eat almost anything if their population is high and they are running out of food. That happens most often in times of drought or near the end of a colder-than-normal winter.

Q: We have a six-year-old crape myrtle in our shady back yard. It bloomed well the first three or four years. Now the new leaves are curled and flowering has dropped off. We also see some cobwebs; is that from spider mites? Can we spray to fix these problems?

A: If your crape myrtle is in a shady location, it will not bloom well, if at all. If the shade is from trees, the location most likely has poor air circulation as well, which may promote a disease called powdery mildew. Typically, the flower clusters are affected as they begin to develop with a white film on the developing buds and the leaves near the ends of the branches. The disease may also distort leaves and clusters of buds, or even prevent their further development if it is severe enough.

Most modern crape myrtle varieties have a high tolerance for powdery mildew in satisfactory growing conditions. Given a lack of sunlight and air circulation, a disease-resistant plant may still be damaged by disease.

As for mites, they are not often pests of crape myrtles, at least not outdoors where rain washes them off the foliage and a host of predatory mites and insects feed on them.

Move your crape myrtle to a sunnier location in late winter, and it should bloom better next summer.

Q: I would like to create a vegetable plot in a sunny part of my yard, but the area would be about 10 feet from an old pressure-treated fence that probably contains arsenic. Would it be safe to grow vegetables in this vicinity?

A: Most vegetables like soil that has a neutral pH or is slightly alkaline, conditions that diminish the risks of arsenic contamination. Arsenic is bound to aluminum and iron in soil, and the resulting compounds are not very soluble in neutral or alkaline pH soils. You can test the soil for arsenic (and pH), but it is unlikely to be in the high range unless the area served as a site for dumping of industrial wastes containing arsenic. This would be evident by the failure of most plants to grow in the site.

At any rate, the distance between the fence and your new garden would be too great for any significant amount of arsenic to travel through the soil.

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

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