GARDENER'S MAILBAG: Let's talk goatheads
Dear Neil: What is the best way to get rid of goatheads?
When people use the name “goatheads,” I always clarify if they’re talking about grassburs (“sticker burs”) or the much more sinister weed with spines strong enough to puncture volleyballs and bicycle tires. If the latter, those are the true “goatheads.” They are broadleafed weeds with leaves that don’t look anything like blades of grass. Grassburs, by comparison, are true grasses. Their slender, simple and elongated leaves have parallel veins. So, all of that out of the way, you can use a broad-leafed weedkiller (containing 2,4-D) to eliminate goatheads at any time that you see them growing actively, preferably earlier in the growing season than August. Grassburs can only be prevented, and that requires application of pre-emergent weedkiller granules in late winter (two weeks prior to the average date of your last killing freeze) and again 90 days later. Three common pre-emergents are Dimension, Halts and Balan.
Dear Neil: We’ve had this fig in our family for many years. This past winter was hard on it, but it’s coming back, and it’s bearing fruit. Should we cut the dead limbs off now or wait until the winter dormant season?
Trim them now. Make each cut flush with a healthy branch. There is no point in waiting. Reshape the plant as needed to restore an attractive form. If it involves trimming new growth, that pruning probably could wait until late winter so that you don’t encourage a flush of new growth going into cold weather. But dead shoots can be removed at any time.
Dear Neil: Why would this water oak be yellowing? Is it a fertilizer or mineral issue?
I consider those to be the same thing. Fertilizers we add to our plants are mineral salts. But you didn’t tell me where this tree is growing. That could definitely matter. You also didn’t tell me if it looked perfect going into last winter. Water oaks must have acidic or neutral soils to hold their attractive green color. Iron becomes insoluble in soils that are alkaline, and plants that need a great deal of iron start to turn yellow. So, if you told me that this tree looked a bit yellow a year ago, that would be my guess. Unfortunately, when water oaks begin to show iron deficiency due to alkaline soils it’s usually time to change to another species. It’s difficult to get enough iron into the tree to correct that particular problem. On the other hand, if the problem has only shown up this year, and if the soil is known to be acidic, then the yellowing is probably due to freeze damage from the February cold. (See answer to next question.)
Dear Neil: Is it a good plan to fertilize oak trees that were damaged by the February cold?
Foresters advise that we leave them alone for the rest of this growing season, just allowing them to repair themselves. Their prime need will be water during dry spells. Trees that have half of more of their normal leaf canopies should be fine. Those that have lost more than half of their normal leaf count are more likely to have suffered permanent setback.
Dear Neil: What is this weed, and how can we control it? It’s invading our St. Augustine lawn.
This is Virginia buttonweed, and it’s one tough cookie. It’s aggressive, and it’s resistant to most herbicides. Combination broadleafed weedkillers that contain 2,4-D will help with it, but you’ll want to try a small area first to be sure (a) that it kills the buttonweed and (b) that it doesn’t damage the St. Augustine. You may get some control with applications this fall, but you’ll almost assuredly have to treat again in the spring. Use a pump sprayer (finer droplet size), not one that attaches to the end of your hose.
Dear Neil: We planted a Chinese pistachio last fall. It leafed out this spring, but it has declined over the summer. We’re not sure if the cold killed it. Should we just try again this fall?
That’s a good plan. It was so new to your landscape that the cold probably was more than it could handle. Most Chinese pistachios in Texas came through just fine. They’re lovely shade trees – definitely worthy of a second try.
Dear Neil: I’m growing 25 red oaks in 3-gallon pots. They were all volunteers and I couldn’t stand to see them mowed down. How often do I need to water them this winter? How tall do they need to be before I can give them to friends to plant into their landscapes?
Frequency of watering will depend on temperature, wind, humidity, potting soil and plant size, but in the winter you probably won’t have to water more often than once per week if you do so thoroughly. They can be planted into landscapes when they are 36 or 40 inches tall as long as they are staked to prevent wind or equipment from breaking them off.
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