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TEXAS GARDENING: Fall is a great time to prune trees to avoid disease

TEXAS GARDENING: Fall is a great time to prune trees to avoid disease

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Dear Neil: I need to have some pruning work done on my red oak. Is fall a good time to do so? What time is best?

A: This is an outstanding time, because the vectors that spread oak wilt fungus are inactive in the winter. Spring is taboo, as oak wilt fungal mats are active in infested trees, so that is the season of most active transmission. Pathologists tell us that mid-summer, during the hottest weather, is another suitable time to prune. Hire a certified arborist with experience in oak wilt issues. That’s especially critical if the disease is active in your area.

Dear Neil: We have a boxwood hedge that was planted in the mid- to late 1950s. Besides trimming it as needed and watering it, what nutrients can we add, and what else should we do to keep it going?

A: You have named the two most important things. Apply a high-nitrogen fertilizer in early spring, again in early summer and in early fall. Trim it several times each growing season to keep it full and compact. Hopefully you will not have to do major pruning to reduce its size. If that should become necessary, do it very carefully, and do it in late winter, before new growth begins for the spring.

Dear Neil: I plan to convert about half of my backyard from bermuda grass to mulch. What is the best plan to kill the bermuda? The area includes a recently planted oak, which I will keep. I have cleared the bermuda away from the tree about 18 inches out all the way around. Is that enough to protect the tree?

A: You would want to use a glyphosate spray to kill the existing bermuda grass without contaminating the soil. It’s imperative that you get a herbicide that contains only glyphosate — no other active ingredient. If you’re going to be spraying near the oak tree, wrap its trunk with aluminum foil up about 15 inches. You can remove the foil the next day. You must do the spraying before the bermuda grass goes dormant following the first killing freeze.

Dear Neil: I planted new pansies, and about two weeks later they started to die. When I pulled on them there were no roots at all. The leaves were starting to yellow. Someone suggested it was a fungus, but I found no evidence on the plants. Help!

A: That sounds like one of the water mold funguses. They attack pansy stems near the ground line after they have damaged the roots severely. It could be Pythium or Rhizoctonia, or it might be the two working in tandem. It helps if you prepare the bed 8 to 10 inches deep and mound it 4 or 5 inches above the surrounding grade. Work in several inches of organic matter and 1 inch of expanded shale. All added together, that will ensure good drainage.

Dear Neil: We and our neighbor have live oaks with these spots on their leaves. The trees look healthy, and there is no sign of die back. What is it, and how should we treat it?

A: I believe this is nothing more than old damage of oak leaf blister from last spring. It was rampant following the rains. These leaves will be shed in a couple of months anyway, so I would not be particularly concerned at this point. The long-term health and vigor of the trees will not be compromised.

Dear Neil: If this were your tree, how would you trim it? How would you care for it in general terms?

A: I would trim off all the deadwood. I would trim off any of the living twigs that caused the tree to be misshapen. I would remove the sprouts at the base. I would use paper tree wrap to protect the trunk against sunscald from the ground up to the lowest branch. Hopefully you are not too late already. All new oaks should be protected in that way for the first two years in their new homes.

Dear Neil: Do I need to be concerned about English ivy that is growing up the trunk of our very nice, old Heritage live oak? Someone has told us it could choke out the tree, and that it adds to the weight of the tree’s branches. Should I remove it?

A: The only two times I get really concerned about English ivy climbing up the trunks of my trees are when it starts to grow out horizontally onto the limbs (because it does add to the weight of the branches during wind and ice storms) and when it starts to form a canopy over the top of the tree (since shading will kill out the support tree). It is not parasitic, and it does not cause any harm to the bark of the tree. If you keep it pruned so that it’s only on the trunks, it should be fine.

Dear Neil: Would it be possible to get grass to grow on top of an old concrete slab? We have six dogs. I’m not physically able to break the concrete, and I can’t afford to hire a landscaper to do it. How much soil would I have to add?

A: That is probably not a good plan. You’d be better off giving the dogs some space immediately adjacent to the slab, and then to concentrate your efforts on getting the grass to grow there. You would need a foot of topsoil before you would be able to grow grass, and even then, drainage would be a concern with solid concrete below. Dogs will trample your grass, and you would be left with a foot or more of mud every time it rains. The dogs will be fine on the concrete, and it will be a lot easier to keep it (and them) clean. If you absolutely must have grass there, ask a scout troop or church group to help break up the concrete. Adults could break it, and the teens could cart it away.

If you’d like Neil Sperry’s help with a plant question, drop him a note in care of The Eagle, P.O. Box 3000, Bryan, Texas 77805. Or email him at

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