What to look for when buying a crab apple tree this fall

BACKYARD Q&A

September 30, 2001|By Dennis Bishop | Dennis Bishop,SPECIAL TO THE SUN

Q. I have seen many varieties of flowering crab apple for sale at local nurseries and would like to plant several this fall. What characteristics should I look for when selecting a particular variety?

A. There are several things to consider when selecting a crab apple tree. First, because crab apples vary greatly in their susceptibility to disease, I would be sure to select a variety that has good disease resistance. The trees you select should be resistant to apple scab and fire blight, the two most important diseases of crab apple. Second, I would consider the size and shape of a particular variety. Crab apples vary greatly in both of these characteristics. For example, some dwarf varieties may grow only 6 feet tall, while other varieties may grow 25 to 30 feet tall. Finally, I would consider the characteristics of the flowers and fruits. The flowers may be white to pink to red. While the fruits are typically red, some varieties have orange or yellow fruits.

Q. I have noticed some small trees planted along city streets that have green cone-shaped bags tied to the trunks. Do you know what these are used for?

A. Yes, these poly-mesh bags are used for watering newly planted trees. They function as a portable drip irrigation system. When the sacks are filled with water, they slowly release the water through holes in the bottom. This is an efficient way to get water around the tree's root ball where it is needed after planting. The sacks are not designed for watering larger, established landscape trees.

Q. In a recent column you described a blight disease that affects beds of pachysandra. I have a similar problem in my bed of vinca. Is it the same disease?

A. No, it is not the same disease. This is another example of the fact that most diseases are specific to certain plants or certain closely related plants. The disease in your vinca (sometimes called myrtle or periwinkle) is most likely a root and stem rot that is caused by the fungus Pellicularia filamentosa. It is very common, but is most destructive of plantings in heavy, poorly drained soils and during wet weather. To control the disease, all diseased plants should be removed and an effort should be made to improve drainage. Also, I would not water vinca unless the soil is very dry.

THIS WEEK'S CHECKLIST

1. Be sure to keep fallen fruits cleaned up from under your plants. They can be a source of disease for next year's crop.

2. Now is a great time to begin preparing beds for next spring's garden. The soil is easy to work during dry weather in early fall.

3. Do you want to enrich your leaf compost? Food scraps of fruits and vegetables are a great addition to the compost pile. When turned into the pile, they are a source of nitrogen, phosphorus and potassium.

Dennis Bishop is an urban horticulture educator for the Baltimore office of the Maryland Cooperative Extension Services. If you have a gardening or pest problem, you can call the Home and Garden Information Center hot line (Monday through Friday, 8 a.m. to 1 p.m.) at 800-342-2507. You can also e-mail questions, order publications and diagnose plant problems by visiting the Web site, www. agnr.umd.edu / users / hgic.

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