Dear Neil: I've had three cleyera shrubs that have done well for 10 years, but one has started to thin and look sickly the past 15 months. What bothers them? I see no signs of insects or diseases. Do they need fertilizer?

Answer: Cleyeras have somewhat weak root systems, so anything that causes root loss will be magnified in cleyeras.

The droughts of two and three years ago hurt them badly. Curiously, so did the prolonged wet weather last spring and early summer. My bet would be that your plant's problems are related to one of those, probably the latter.

The problem is unlikely to be related to soil fertility.

Q: I have a several-year-old listing of pecan varieties and their suitability to eastern and western regions of Texas. It also tells whether they have pollen or nutlets first (important in pollination). I need information on two other varieties: Nocona and Pawnee. I have property in both parts of the state. Where do these grow best?

A: Womack Nursery in DeLeon produces pecan transplants for commercial orchards and home gardens. It lists both of these as eastern varieties in its latest catalog. Pawnee sheds its pollen first. Nocona produces its pollen later.

Remember Caddo as an eastern variety (pollen first), too. It is highly recommended by Texas A&M University pecan authorities.

Q: What is the best way to eliminate grape hyacinths that have invaded my lawn from the next door neighbor's flower beds?

A: This will take patience. Spray a broadleaf weedkiller to the grape hyacinths' leaves during times when they are growing most actively. You will have to treat several times.

Take care of your turf, too, to help it crowd out the flowers.

Q: I had a retama tree in my flower garden in Corpus Christi. How far north will they grow? I liked its look plus the fact that it didn't cast a lot of shade on my flowers.

A: Retamas (Parkinsonia aculeata) are hardy in Zone 8b. That means you will see them most commonly from College Station to Austin and southward. North of that area they are subject to freeze injury in extreme winters.

They grow so quickly, however, that you may decide they're worth the slight extra effort. You will probably have to start yours from seed. They are seldom seen in nurseries.

Note that this species is much-hated in some tropical areas because of its invasive habits. That isn't a problem in most of Texas.

Q: My Bermuda grass lawn is thin and unattractive. I tried mowing it much shorter (1.5 inches tall) from mid-summer on last year. I aerated it last year, but to no avail. Should I put a layer of organic topsoil over it this year? If so, when? If I sowed more seeds, should I put them down before or after the topsoil? What fertilizer and weedkiller should I use?

A: First things first: Bermuda needs six to eight hours of intense, direct sunlight daily. If yours isn't getting that much, that and that alone is the problem.

But let's assume that it's in full sunlight. Start this season with your mower set to the lower height. Hopefully you'll be able to leave it there. When you mow Bermuda grass higher than 1.5 inches it will tend to thin, and you'll see the browned stem stubble for several days after each mowing.

Mow it frequently (four- to five-day intervals) during the period of most active growth. Apply a quality, high-nitrogen or all-nitrogen plant food at eight-week intervals from April 1 through Oct. 1.

You can use pre-emergent weedkillers to stop germination of weeds such as crab grass and grass burs in the summer and annual bluegrass, henbit, dandelions and clover in the winter. Use a broadleaf weedkiller to eliminate existing non-grassy weeds, and use MSMA, if needed, to eliminate perennial grassy weeds such as dallisgrass. That spray would be made in early summer.

You should not need to spread topsoil unless you need to even up the soil's surface. You should not overseed Bermuda with more Bermuda seed. It is too fine to grow successfully under those conditions.

• If you'd like Neil Sperry's help with a plant question, drop him a note in care of The Eagle, P.O. Box 3000, Bryan, Texas 77805. Or e-mail him at mailbag@sperrygardens.com.

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