Richard Nunnally’s gardening column

Q:Please let me know how I can get rid of poa annua in my lawn. Mine dies down in the spring but comes back strong the following year.

Answer: Poa annua is annual bluegrass. As you have discovered, it is very difficult to control. It started dying several weeks ago, but all of the seeds it dropped will germinate next fall. Because it's an annual, the ideal way to control it is with a pre-emergent herbicide applied in late August or early September. Of course, that means you can't plant fescue seeds at that time either. Poa annua seeds normally germinate in midto late September, based on temperature and availability of water. If you decide to use the pre-emergent in September, you may want to buy it now. Many garden centers don't carry it in the fall.

Q:How do I avoid that awful black bottom on my tomatoes? I live in western Hanover County, and every year my first tomatoes have this problem. Later in the summer, it seems to clear up on its own.

Answer: The black spots are symptoms of blossom end rot (BER). They are caused by a calcium deficiency in the plant. This can come from irregular moisture, too wet followed by too dry, or from too much nitrogen. The nitrogen causes the plants to use up their calcium making leaves and stems, and they don't have enough left for the fruit.

One way to prevent it is to make sure your soil has plenty of calcium to begin with. Next, don't overfertilize the plants. Feed them once or twice when you plant them, and then don't feed them anymore until the first tomatoes get about the size of a golf ball. You can also mulch your plants when the ground starts getting hot to help conserve moisture. After all of this, if you still get some BER, pick off any tomatoes that have the spots as soon as you see them. The spots will only continue to get larger, ruining even more of the tomato. This will also allow the plant to produce a second set of tomatoes. Normally, BER is not a problem on the later tomatoes, because the lush growth period of spring is over and they are no longer producing excess foliage growth.

Q:My husband and I really love mountain laurel. However, we haven't been able to find it at any of our local garden centers. Do you know of a nursery that sells them?

Answer: The botanical name for mountain laurel is kalmia latifolia. The Historyland Nursery in Warsaw grows several varieties, and the Glen Allen Nursery in the Richmond area grows at least one variety. Both of these nurseries are wholesale growers, but you may be able to buy directly from them. If not, I'm sure they can tell you if a retailer in your area carries their mountain laurel.

Q:We have always bagged our grass clippings to make the lawn look better and to prevent thatch buildup. We recently picked up a pamphlet from the Extension Office on lawn care, and it recommended leaving the clippings on the lawn, saying they provide nutrition as they decompose. What do you recommend?

Answer: I don't bag my clippings. There has been a significant amount of research that shows that allowing your grass clippings to stay on the lawn and decompose can provide about 25 percent of the fertilizer you need in a year. Of course, that requires that you mow your grass regularly and don't allow the grass to get too tall before you mow it.

As for the thatch, I have seen the results of several studies that showed lawns actually developed less thatch when the clippings were left on the lawn. It seems that fresh clippings are very high in moisture and nitrogen. As they decompose, they actually help to speed the decomposition of the material that could become thatch.

Richard Nunnally is a freelance writer and host of WCVE's monthly gardening show, "Virginia Home Grown." He can be contacted at .