ANSWER: Those are fungal gnats, and they live and breed in the algal mass (“moss”) that grows on the surface of potting soil and even on the surfaces of flowerpots. They’re especially annoying, but harmless to your plants. They’re not feeding on the plants themselves, so systemic insecticides like what you probably applied will have no impact on them. They suggest that the potting soil is being kept consistently too wet. You either need to cut back gently on the amount of water you apply, or (probably better) lengthen the intervals between waterings. Don’t overdo it — you won’t have to make much of a change in watering to have big impact on the gnat population. Finally, the most important and most immediate thing you can do is to repot each of your plants into cleaned or new flowerpots that have no algal growth. Use a table fork to “comb” away the top quarter-inch of soil from the potting soil, then replace it with new potting soil.
DEAR NEIL: We’re having trouble finding a new bois d’arc tree to replace one that will soon fall down in our garden. Nurserymen don’t seem to sell them. Can you offer any suggestions?
ANSWER: I took it one step farther. I just did a web search for “buy fruitless thornless Maclura pomifera” and came up with many matches, so we know that they are out there. I suspect that most retail nurserymen just wouldn’t see enough traffic asking for them to justify keeping them in stock. You could try native plant nurseries, also those that specialize in large assortments of unusual types of trees. At one point in time, Fanick Nursery in San Antonio offered such a selection. You could check with them.
DEAR NEIL: I have several oak trees that vary in size from 3 to 6 inches in trunk diameter. Would it still be advantageous to mulch these trees? If not, at what point should we stop?
ANSWER: Mulching is always appropriate for any size of tree. However, the larger a tree grows, the less critical it is. For the first two or three years, as trees are establishing good root systems, mulching really helps in the process. By the time they’re well-rooted, however, you can probably switch over to turf or to a shade-loving groundcover.
DEAR NEIL: What are the things that look like okra pods that have followed yucca flowers in our neighborhood this year? Are they related to the drought and heat from last summer?
ANSWER: Those are the fruit, and the seeds for another generation of yuccas are contained within them. It happens most years, but when conditions are very dry, the plants will be less able to bloom, therefore produce seed.
DEAR NEIL: Every summer we get a ton of sticker burs in our yard at our vacation place. What can we do to get rid of them? We’re heading there soon, and they are so painful.
ANSWER: Grassburs can be prevented, but there is no control for them once they germinate and start growing. Mow frequently to keep the seed heads (stickers) from forming. Then, early next March and again early next June, apply a pre-emergent herbicide to keep the next generation from germinating in the first place. Dimension, Balan or Halts will all work well, but you must make both treatments. The products are effective for about 100 days, and the germination/growing season for grassburs is twice that long, hence the double treatment. And, applying the granules only in June will have little, if any, effect, since most of the plants are already growing. Tip taught to me by my dad: when you have to pull grassburs out of your clothes, carpeting, pet’s fur, etc., moisten your fingers first. It softens the points just a little, and that makes the task somewhat less painful.
Have a question you’d like Neil to consider? E-mail him at firstname.lastname@example.org. Neil regrets that he cannot reply to questions individually.