Paul James, host of
Gardening by the Yard and a master gardener, fields some gardening questions:
Q: Just the other day a gardening authority said that grass clippings create thatch, yet I've also heard that grass clippings have nothing to do with thatch. Which is it?
A: Anyone who believes thatch is caused by grass clippings is about 10 years behind the latest research on the subject. Having said that, let me add that an excessive buildup of grass clippings on the lawn--those left by a nonmulching mower, for instance--can lead to problems because they can smother the soil and prevent water from seeping into the grass's root zone. But thatch is a different problem altogether. Thatch is a layer of grass roots and stems--some living, some dead--that form a mat near the soil surface that water and nutrients can't easily penetrate. Thatch is caused by two things: poor watering practices and the frequent use of quick-release fertilizers.
When you water the lawn frequently but for only 10 or 15 minutes at a time, the water never gets a chance to seep down deep into the subsoil so grass roots remain near the soil surface, where the moisture is, and begin to form a mat. When you feed the lawn with a quick-release fertilizer, the nutrients tend to remain near the soil surface as well, so the roots do too. In time you wind up with thatch. All lawns have some amount of thatch, which isn't necessarily a bad thing. But when thatch buildup becomes excessive--thicker than 1/4-inch thick--problems can result.
Fortunately, getting rid of thatch is relatively easy. All you need is a thatch rake: pulled across the lawn a few times, it will rip right through the stuff. Those with large lawns or serious thatch buildup can use a mechanical dethatcher. Once you've dethatched your lawn, switch to slow-release lawn fertilizers, and deep soak the lawn each time you water. Your thatch problem will be history.
Q: How do I know when to water?
A: Pay attention to the clues nature provides. First, look for signs of stress in the grass, which indicates a lack of water: the most visible sign is a discoloration of the grass blades. When the blades turn from glossy green to a sort of dullish blue-gray, it's time to water. Likewise, if the leaf blades begin to curl from the sides, it's time to water. One of the easiest and most dependable ways to determine when to water is to walk across the lawn and observe your footprints. If imprints remain after five seconds or so, it's time to water.
Q: I live in the Midwest, and no matter how often I water, my Bermuda lawn turns brown in the middle of summer. How come?
A: Although it's a warm-season grass, Bermuda has a tendency to enter a period of heat-induced dormancy during the scorching summer months. As you've discovered, the browning occurs no matter how much you water. That's because a lack of water isn't the problem. The problem is that the sun's rays are so intense that the grass simply says it's time for a siesta. There's no need to panic, however, because after a few days of cloud cover or cooler weather the grass will bounce right back. Stick with a regular watering schedule in the meantime, but don't fertilize, which would stress the grass even more.
Q: What's with the caterpillars that keep attacking my parsley? They're beautiful, but they have ravenous appetites.
A: The pest described is called the celeryworm or parsleyworm, depending on which plant it happens to be attacking. The worm is the larval form of the gorgeous black swallowtail butterfly. When disturbed, it tries to look tough by projecting two orange horns from its head, but it's totally harmless. I encourage hordes of them to hang around by simply planting more parsley than I can consume and letting them eat all they want. However, if their populations get out of hand, you can easily control them by hand-picking or by applying the live bacteria Bt, or Bacillus thuringiensis, available in powder and liquid form wherever lawn and garden products are sold.
Q: Each morning and evening my container plants look fine, but during the middle of the day they look wilted, no matter how often I water them. What gives?
A: That's a problem with container plants during the summer months. The source of the problem can usually be traced to two things. First, the pot may be too small to support the plant, as in the case of my pineapple sage. I initially put three plants in the pot, and after a few months, they simply outgrew the space. Another factor could be reflective heat. Many container plants are placed on concrete surfaces, and the temperature around them may be as much as 20 degrees hotter than the air temperature as a result of the sun's rays bouncing off the concrete. That places considerable stress on plants, even if the soil is moist. It's also possible that it's just too hot outside during the middle of the day, so you might want to consider moving the most venerable plants to a shadier spot, where they'll get only morning sun.
Q: What is sun-scald, and how do I prevent it?
A: Sun-scald is a condition that occurs during the winter months, and young maples are very susceptible. The sap within the bark contracts during cold periods, but when the sun comes out and hits the bark--even when the air temperature is in the 40s--it causes the sap to expand. If the expansion takes place quickly, it can cause the bark to split. To prevent sun-scald, you can do what my grandmother did: paint the trunks of the trees white to reflect the heat. But that makes for a silly looking tree, so here's a better alternative: wrap the trunk of the tree with one of several products on the market aimed at preventing sun-scald. The best wraps are porous, and the wrap should extend from the bottom of the trunk up to the first set of lateral branches. Wraps should be installed in early fall and removed in early spring.
Q: What is gypsum, and does it really loosen heavy clay soils?
A: Gypsum is calcium sulfate, and it's been recommended for decades to improve the texture of clay soils without affecting the pH. Does it work? In time, perhaps, but you're far better off adding lots of organic matter such as compost or shredded leaves. If you want to add gypsum in the process, go ahead, but don't rely on gypsum alone to solve the problem.
Q: I've heard you shouldn't put mulch all the way up to the trunk of trees and shrubs or to the base of flower and vegetable plants. Is that true, and if so, why?
A: If you pile mulch right up to the base of tree trunks or flower and vegetable stems, you encourage rot. For that reason most folks suggest you keep mulch at least six inches away from tree trunks and at least one inch away from the base of flowers and vegetables.
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