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DEAR NEIL: I am enclosing two leaves from my gardenia. They are totally blackened. Because the stuff rubs off, I thought I could wash it off with a soapy water spray, but it didn't work. What causes it, and what can I do to remove it?

That's the same sooty mold that grows on other plants' leaves and stems. It is always a secondary invader, meaning that it is invited on each plant by some other issue, almost always from sap dripping on the leaves and twigs.

In your case it's because the gardenia was loaded up with whiteflies last season. They're the small, swarming insects that coat the backs of the leaves with their egg cases. Every time you brush against the plant you'll encounter an armada of the pests. Use a systemic insecticide such as acephate on 10-day intervals to protect the new growth. There is nothing you can do other than hand-washing the leaves to remove the residue from the old leaves. New growth will be clean until another infestation coats the leaves with the honeydew. Aphids and scale insects cause similar problems on other plants.

DEAR NEIL: What is your opinion of bagging or mulching my grass clippings?

I can make a strong case for either. Personally, I collect my clippings and use them in my compost and as a dry mulch in shrub beds. On the other hand, if you mow frequently, and if you use a mulching mower that regrinds each clipping several times so that they're fully pulverized, you can leave them in place to release their nutrients back into the soil. The non-negotiable part of all this is that you must not send them to the landfill.

DEAR NEIL: Over the past several years I have watched my lawn thin out beneath several large live oaks. I have grass growing under other trees in other parts of my yard and it seems to be doing fine. Have you seen this? What might the cause be? All of my lawn is St. Augustine, and it's all treated equally.

This is the most common question I'm asked about lawns: how to handle thin grass beneath trees. No trees that you grow cast any heavier shade than live oaks, and you're seeing the natural progression of the thinning as the shaded area grows larger. No grass is more shade-tolerant, so it's probably time to think about a shade-loving groundcover. I have many, including mondograss (my personal choice for big areas), liriope, English and Persian ivy (problems with last year's really wet soils), Asian jasmine, purple wintercreeper and ferns.

DEAR NEIL: We have lived here for three years, and our bermuda lawn has had dead spots each summer. The lawn people have told me it's from salt leaching up and causing a white substance to appear. What can we do to neutralize the salt?

Begin with a complete soil analysis from the Texas A&M Soil Testing Laboratory. They will not only determine your soil's nutritional levels, but they'll also identify its pH (acidity or alkalinity). Most importantly, you will also see its concentration of soluble salts. Ask that they interpret each result for you. Total charge will be $25-$40 for the test, and it will prove or disprove whether the soils are at fault. Contact your County Extension office for the sample bags, mailing boxes and instructions.

Be sure the drainage in the area is good so that excess mineral salts of all types can leach out of the soil, then water heavily to rid most of them.

You may end up using gypsum to replace the sodium on the soil particles with less harmful calcium. Finally, you may find that there are outside issues entirely that are causing the dieback. They might include bermuda mites, a fungal problem, mowing too high or excessive shade in certain portions. It's a witch hunt. Good luck on it.

DEAR NEIL: I am originally from Oregon. I had a moss garden there. How can I get one started here? I'm now a retired gardener basking in the Texas climate.

That climate is not the ally of a moss gardener. Moss grows luxuriantly in Texas during cool winter and early spring weather. It's especially common in the eastern half of the state where the humidity is usually high.

However, once it turns hot and dry, moss goes completely dormant and turns insipid greenish-brown. You won't see the same kind of moss gardens in Texas that you were used to in the Pacific Northwest. That's just a completely different kind of climate. Concentrate, instead of some of the lowest sedums, dwarf mondograss and other ultra-low groundcovers.

DEAR NEIL: Four years ago our granddaughter requested a willow tree for her birthday. We bought one, and it did fairly well for two years. However, it then began to weaken and finally fell a few weeks ago. It was full of insects. Is there a better kind of willow that wouldn't have these problems?

Cottonwood borers are a horrible problem with willows (also cottonwoods and poplars), enough so that the average life expectancy of a weeping willow in a standard landscape setting is probably only 5 to 7 years. Most other willows would be about the same.

Willows can be rooted in water by using stem cuttings, but the pertinent question probably should be: would you show your granddaughter a better example if you bought an oak of an adapted species to emphasize quality and durability of trees? If I were giving a tree to one of my grandkids, it would definitely be an oak.

DEAR NEIL: Grape hyacinths are so pretty in the spring, then they go away for the rest of the year. Even henbit is pretty for a couple of weeks, as are other flowers I can't even name. But, we cater to our water-consuming lawns filled with grasses that are not native and that require fertilizer.

What better solutions do we have?

First of all, the assumption that grasses don't carry their own share of the load in our landscapes is not correct. It would be a sad landscaping day if we didn't have turf for recreational spaces, for its cooling effect, for erosion control and for simply unifying our garden designs. And, "native" isn't always synonymous with water-conserving. I offer cottonwoods and willows as examples. Johnsongrass is native, yet it guzzles the water.

Common bermudagrass is a great compromise: a grass that is drought-tolerant, but also one that's good-looking and durable. I will acknowledge that we over-water and over-feed our lawns, but we shouldn't over-correct as we strive to right our ways.

DEAR NEIL: We have property on a caliche hill in Central Texas. We brought in soil to create a yard, but we couldn't put it around our oaks for fear of damaging them. I tried liriope and mondograss beneath the oaks, but the bermudagrass has overtaken them. And, we have oak sprouts all over the place. How much soil can we add to deal with the roots, and how can we cope with the bermudagrass?

Even with large trees in deep soils, 90 percent of their roots will be in the top foot of soil. After all, that's where rainfall hits, so they're there to compete. We must never add more than one inch of soil over a tree's root system. It will compact and drive available oxygen out of the soil. As for the bermudagrass, there is no easy way to eliminate it from liriope and mondograss. If it were mine, I would probably dig it all up, then carefully work through the plants to remove the grass. I would work organic matter into the soil and replant. However, if oak roots were in this same area, I would probably try to figure some attractive way of discouraging their growth. I might put a layer of roll-type mulch down, then cover it with attractive, small river rock. I'd figure a way of including large, decorative pots in the area for added interest. Take photos to a Master Certified Nursery Professional for addition suggestions.

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.