What is crown gall?
Arborist Guy LeBlanc says it’s usually caused by a bacterium, but some experts say other causes are possible. The source of entry is usually some kind of wound, oftentimes nematodes or other insects that invade roots. Some galls that occur low on a trunk can actually be fungal galls. Guy also confirms that the white insects in the picture are termites. He’s often seen them infest crown galls, but says that they won’t harm the living portion of the tree, as our local termites just invade the dead tissue. Guy has consulted with entomologists who do not recommend treating the termites. Guy concludes by telling us that most trees that he’s seen with crown gall survive in very good condition without treatment, but he’s also seen some that slowly decline over many years. And unfortunately, there is no successful treatment for crown gall that he knows of. So, our advice is to keep the tree healthy, well-watered, correctly pruned, and to avoid damaging the bark.
Can you cover twelve-year-old oak tree above ground roots with compost?
Since exposed tree roots are pretty common, I imagine many people may have this question. Those exposed roots can actually be a hazard, so if you can cover them, you definitely should. And if the tree is in the middle of the lawn, the roots are also in the way of the mower and can get nicked, which wouldn’t be good. Building up the soil over those roots and planting a ground cover, one that doesn’t need to be mowed, is a great idea. Just make sure that the soil/compost or mulch that you add doesn’t touch the trunk, and that you don’t apply it too thick. Two to four inches is a good amount, but don’t apply more than that—you don’t want to cover those roots too deeply. I’m sure you’ve noticed how bark-y the exposed roots are. Although they once took up water and nutrients for the tree, now they serve as support, and are connected to the feeding roots, which are found at the dripline of the tree, out past the furthest branches. If you do plant a ground cover over the exposed roots, be careful not to damage the roots if you ever choose to dig around in that soil. A wounded spot will allow for the invasion of fungi and bacteria that could damage your tree. And a large cut might result in die-back in the part of the tree connected to the cut root.
Advice on sprucing up a neglected landscape
Viewer Diane says that their home was vacant over a year and a half before they purchased it, so the yard is really out of shape. Well Diane, the best place to start would be your soil. If the landscape has not been irrigated since the house was vacated so long ago, the soil is going to be very compacted. So you should plan to rent the proper equipment, or hire someone to aerate. Then, put the landscape back on a regular irrigation schedule. Even watering just once a month, if we aren’t getting any rain, will go a long ways toward keeping your soil from drying out completely and shrinking in on itself. Compacted soil is like rock to a plant’s roots, so growth is really inhibited. But aeration will create nice little holes where irrigation water and oxygen can move into the soil more easily, helping to soften it up. As for the weeds, keep pulling them, as you say you’ve already started, and use mulch around any established trees and shrubs, or any plants that you intend to keep. Diane wanted to know about putting down newspaper under the mulch, and yes, that’s a great idea. Mulching alone does help to inhibit weed growth, but really only works if the weed seeds haven’t yet germinated. Once the seedling emerges, the plant usually has plenty of stored carbohydrates to push up through your mulch, reach the sun, and grow by leaps and bounds overnight. A layer of newspaper, one section or 6 to 10 pages will usually do the trick. The newspaper barrier is a little harder for weeds to push through, although not impossible. Be sure to moisten the newspaper before you put the mulch on top of it. If we get lucky and get a hard rain soon, your mulch will wash right off of the dry newspaper in a little avalanche.
Can you mulch on top of live oak leaves that have fallen into garden beds, rather than rake them up?
Viewer Robin usually removes them, since she’s heard they don’t break down easily. Well, Robin, I’d say that leaving them is just fine. You’re correct that live oak leaves don’t break down easily, but that’s okay, if they’re serving as mulch. My only caution is regarding the possibility of overwintering insects. If you noticed any sort of prolific insect infestation last year, such as caterpillars, I would suggest removing the leaf litter, and either composting it or recycling it curbside. But if you didn’t have any problems last year, it’s not likely that any overwintering insects that may be hiding in your leaf litter will pose enough of a problem to worry about. Especially since our winter was so dry. I also got quite a few questions this winter about live oaks losing their leaves incredibly early this year, and whether this was due to the very early arrival of spring-like temperatures. Everyone’s live oaks were looking especially healthy at the time, so there was real concern about climate change. But the unseasonably warm temperatures were not to blame; at least, not as they reflect the seasons. The early defoliation seen in otherwise healthy live oaks is not out of the ordinary. There are many things that could cause senescence and shedding of leaves, but our recent drought seasons have certainly played a leading role. This may seem counter-intuitive, since the trees appear to be in excellent condition and not at all drought-stressed, but after many weeks without rain, even a healthy tree begins to prepare for a possibly bleak future. Leaves require water to support, and if there’s no water in sight, many trees will drop their leaves and go into dormancy until the stressful situation passes. Other factors causing early defoliation include insect (mites, aphids, Cynipid wasps, etc.) and disease (rust, tar spot, & other fungal leaf spots) ailments. Healthy trees should tolerate these problems and recover from them.
Thryallis, Galphimia glauca
This drought-tough shrub needs very little water to be happy, making it a great choice if you need to replace any shrubs you might’ve lost to last year’s drought. It gets about 4-6’ tall, and about 4’ wide, so give it plenty of room to spread. It prefers to be in the full sun, but can take part shade. Thryallis also tolerates any soil type but does need good drainage, so if you have heavy clay soil, be sure to amend it, or replace it with a sandy loam top-soil, and be careful not to overwater. Thryallis is covered in yellow flowers from spring all the way ‘til frost, and the leaves are a nice, dark, glossy green. The leaves are small, giving the plant a bit of wispiness in a light breeze. It is listed as deer resistant—a big plus for central Texas landscapes. Thryallis is listed as hardy to only about 25 degrees F, making it a little susceptible to freeze damage, but even when temperatures drop below 25, it’s normally root hardy and will bounce back in the spring. If the plant is freeze damaged, simply prune it back and let the new growth take over. Thryallis may also get overly leggy. If that happens you can either train it to have a more tree-like shape, or prune back the entire plant to encourage it to recover its bushiness.
Texas mountain laurel, Sophora secundiflora
This native shrub/small tree is an evergreen that is extremely drought tough. Even though rain was sparse the past two years, they survived without too much trouble, and recently put on quite a show this year, after our surprisingly wet winter. Mountain laurel is a slow-grower, but well worth the wait. At maturity, it will be 10 to 20 feet tall and 8 to 12 feet wide, so give it plenty room. Since it grows so slowly, it may look lonely in such a large space until it gets big enough to fill it. Resist the urge to plant any other shrubs or large plants around it, but planting a ground cover would be fine. Mountain laurel will bloom better if planted in full sun, but also does fine in part shade. It adapts to most soil types, but prefers rocky, limestone and needs very good drainage. People often ask us why they don’t bloom. Maturity is one reason. And perhaps pruning off new flower spikes, which are brown and not too attractive, leading some people to get rid of them, not fully knowing what they are. Also, Texas mountain laurel can be attacked by the genista caterpillar. In one day, they can defoliate a tree, so be sure to apply Bacillus thuringiensis (Bt) at the first outbreak. Another great reason to choose this plant: it’s deer resistant. The seeds are poisonous if swallowed, but not dangerous otherwise. Once fully mature, the seed pods turn dark brown or gray, and the seeds inside are dark red. The seeds have a very heavy seed coat, making them hard to germinate. But if you wish to try, it’s best to harvest the seed pods before they are fully developed and plant the seeds before they have turned red.
Tatume squash, Cucurbita pepo, ‘Tatume’
This prolific producer is a must-have for any vegetable gardener, especially if you’re converting some lawn space and growing vegetables for the first time. It’s easy to grow and will likely produce more fruit than you can possibly eat. Viewer Caroline sent us these photos from her garden, where she says, and I quote, “I plant Tatume the first or second week of March and the stuff’s coming out of my ears by mid-May.” Tatume prefers to sprawl on the ground, rather than be trellised, so give it plenty of space: 6 to 8 feet on all sides. If you’ve ever grown squash, you’ve come face to face with the dreaded squash vine borer, which destroys squash plants in the blink of an eye. Although it’s not immune to these insects, Tatume does tolerate the damage better than any other squash choice for Central Texas gardens. It also thrives in full sun, requiring very little supplemental irrigation: twice a week deep watering is usually sufficient to keep Tatume growing and blooming, and fruiting through early summer. If you find that you’re getting more squash than you can handle, simply harvest some of the blooms to use in salads. Many vegetables benefit from fertilization throughout production season, but Tatume will perform just fine if only fertilized lightly at the time of planting. Tatume squash is an heirloom variety, so you may have to shop around to find seeds.
Mexican Tithonia, Tithonia rotundifolia, also known as Mexican sunflower
This sweet little sunflower relative makes a great addition to any sunny garden bed. It thrives in our Central Texas heat, but does need a little supplemental irrigation at the hottest, driest times of year. Be sure not to overwater, especially if you have clay soil. And don’t be fooled by its small stature when purchased: Tithonia can get up to 6 feet tall and 4 feet wide, although dwarf varieties are available. The leaves are rather coarse-textured and fuzzy, and the plant will be covered in orange flowers all summer long. If you shear the plant regularly, but lightly, to remove the spent blooms, it will flower even more prolifically. Tithonia is an annual, and can be planted in spring from either seeds or transplants. Since it does get so tall, be sure to put this plant in the back of garden bed, to highlight smaller perennials or groundcovers. Tithonia is irresistible to butterflies, so this plant should be a must-have in any wildlife garden.