Post oak base dying

Dear Neil: This is the largest of 10 oaks trees on our property. It’s the only one with such a high percentage of its leaves turning brown. What is your opinion?

Answer: This is a post oak (Quercus stellata). They are notoriously temperamental about environmental conditions, whether climatic or by things done by humans. Drought, as we experienced last year and especially this year, has done great harm, just as the biblical drought of 2011 did. Not only does it kill post oaks in the year in which it occurs, but it also makes them more vulnerable to a fungal disease called Hypoxylon canker that will weaken them and subsequently kill them one to three years later. Post oaks have perhaps the shortest life expectancies of any oaks.

Dear Neil: My magnolia tree took a real beating in this past summer’s hot weather. I watered it every other day. Any suggestions on how I can get it green once again?

Answer: This summer stressed hundreds, if not thousands of southern magnolias across Texas. It was more associated with drought than with the temperatures. Soak your tree deeply monthly over the next several months. Apply an all-nitrogen fertilizer (no weedkiller included) beneath the tree in April and water it in deeply. Hopefully you will see a steady improvement.

Dear Neil: I saw your reply to an 80-year-old gentleman who lost his large tree in the February 2021 cold spell. You told him to avoid a fast-growing tree and to opt for quality instead. I have almost exactly the same situation and I’m also 80. I can’t afford to wait 10 years for a quality tree to grow. I’ve found a large crape myrtle, also a large vitex. Each is available for $1,000. Any suggestions? (The tree I removed was a Chinese pistachio.)

Answer: Either of those would work. However, they’re not going to cast much shade over a very wide space. You might do a little shopping this fall to see what size of Shumard red oak, Chinquapin oak, live oak, bur oak or cedar elm $1,000 would buy you. Any of those would be excellent exchanges for your pistachio.

Dear Neil: We have several large live oaks in our yard. We had to cut the root of one of them to make a dry creek bed for drainage purposes. Now we have thousands of little oaks sprouting from the cut root. They are coming up everywhere. We remove them and they keep coming back. What can we do?

Answer: That’s a difficult problem to solve. You can’t use any kind of spray because they’re part of the mother tree. If you can slice them off with a machete or a well-sharpened small hoe so that there is no stub of the twig left, you might be able to discourage them. As with crape myrtles, when twigs are removed by cutting flush, they eventually lose their vigor and quit producing sprouts.

Dear Neil: What is digging up my lawn and what can I do to stop it?

Answer: Those are holes from emergence of cicadas and their predators known aptly as cicada killers. Cicadas are the large, noisy insects you see flying in your landscape and hanging on tree trunks. Cicada killers look like large wasps (but they’re harmless unless cornered). You’ll also see them flying around your lawn and landscape at slow rates of speed, hovering close to the ground. When they spot a cicada, they quickly descend upon it, sting it, paralyze it and carry it back to their subterranean nests. Their larvae feed on the decaying cicadas in the ensuing year. No control is recommended. Leave them alone.

Dear Neil: How do you feel about drought-resistant sedges for deeply shaded areas beneath live oaks as alternatives to Asian jasmine or purple wintercreeper?

Answer: I would try a small planting for two or three years before I committed to anything major. While I’m comfortable with regular mondograss and green liriopes in that sort of setting, the ornamental sedges aren’t used widely enough yet, and they haven’t been used long enough for me to have confidence in large-scale recommendations.

Dear Neil: My Mexican olive froze to the stalk last year. I let it grow out without trimming. It used to be a tree, but now it’s a shrub. What should I do now, if anything?

Answer: This makes a pretty plant for anyone in South Texas. You have more reshaping ahead of you. You will need to decide whether you prefer a shrub-form plant or whether you are going to try to retrain it as a tree. If the latter you’re going to have to find a straight shoot to train as the new trunk. I don’t see an obvious choice in your photo. I would probably remove any stubs and overlapping branches and allow the plant to develop as an attractive shrub. (Your plant needs water!)

Dear Neil: I have had Asian jasmine for 20 years. Some is in sun, some in shade. The past winters have set it back. After this summer certain parts have bare sticks and dead vines that result in a thick thatch look. I have watered and fertilized it often. Should I pull out the thatch and replant in the spring? What about the sprigs that are still alive down below but just have dead twigs up above?

Answer: I have never seen insects or diseases bother Asian jasmine. This is assuredly either old freeze damage or drought. Both have done serious damage to Asian jasmine in the past two years. If the bed were mine, I would use my mower to trim it to 3 or 4 inches tall in February, then I would replant the bare areas with well-filled 1-gallon plants in March or April.