Neil Sperry's Mailbag

DEAR NEIL: 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.

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

DEAR NEIL: My bermudagrass lawn is thin and unattractive. I tried mowing it much shorter (1-1/2 inch) 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 would you suggest for it?

First things first: bermuda needs 6 to 8 hours of intense, direct sunlight daily. If yours isn't getting that much, that and that alone is the problem. However, 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 bermudagrass higher than 1-1/2 inch it will tend to thin, and you'll see the browned stem stubble for several days after each mowing. Mow it frequently (4- to 5-day intervals) during the most period of most active growth.

Apply a quality, high-nitrogen or all-nitrogen plant food on 8-week intervals from April 1 through Oct. 1.

You can use pre-emergent weedkillers to stop germination of weeds such as crabgrass and grassburs in the summer and annual bluegrass, henbit, dandelions and clover in the winter. Use a broadleafed 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 of any kind unless you need to even up the soil's surface. You should not overseed bermuda with more bermuda seed. It is far too fine to grow successfully under those conditions.

DEAR NEIL: Last year bermudagrass invaded my St. Augustine.

When should I apply a pre-emergent for it?

Pre-emergent weedkillers work only on annual plants. Bermuda comes back from its roots and runners. Adding further to your problem, anything that kills bermuda will also kill St. Augustine.

The good news is that if you take better care of your St. Augustine in terms of mowing, watering and fertilizing it, it will crowd out almost all grasses, bermuda included.

Have a question you'd like Neil to consider? Mail it to him in care of this newspaper or e-mail him at mailbag@sperrygardens.com. Neil regrets that he cannot reply to questions individually.

Neil Sperry
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