Paul James, host of HGTV's Gardening by the Yard, answers common questions about trees and their care. Q: I've got a mature tree whose roots are growing above the ground, making mowing next to impossible. What can I do? A: You could add topsoil to cover the roots, but in time they'll grow into the topsoil, and if you add too much soil, you could smother the roots and kill the tree. In less severe cases, it's best to plant some sort of groundcover, which will eventually cover the roots if kept well watered. Q: Is it true that deciduous trees should be pruned only when they're dormant? A: It's best to prune most deciduous trees just before they break dormancy, late winter in most areas. But if you make the pruning cuts properly by leaving a branch collar on the trunk rather than making flush cuts, you can prune any time you want. Q: I have a large sycamore in my front yard, and for the past three years it has dropped most of its leaves in spring. What's wrong? A: The tree may have anthracnose, a fungal disease that favors cool, wet springs and causes premature leaf drop in sycamores. You can confirm the diagnosis by looking closely at the fallen leaves (figure A). If they have a white to gray powdery substance on them, the cause is probably anthracnose. You can try to prevent its recurrence by raking up fallen leaves and disposing of them in the trash, not the compost pile. Don't fertilize the tree to encourage new growth, as new tissue is most susceptible to anthracnose. Q: What are some fast-growing trees, preferable deciduous, that will grow in clay soil? A: Many people want fast-growing trees, and unfortunately nearly all of them--for example, silver maples and various poplars, including cottonwoods--are either short-lived or have weak wood. Lacebark, or Chinese, elm (Ulmus parvifolia ) (figure B) is a fast-growing, sturdy tree. Another good choice is any ash (Fraxinus) tree. Q: Each year my apple trees are covered with so much fruit that the branches practically touch the ground. Is it okay to thin the fruit? A: Absolutely. You should thin nearly all fruit trees shortly after they set fruit, unless the trees thin themselves naturally. Ideally, fruits should be spaced roughly 6" apart. Inspect each branch and remove as much fruit as necessary to achieve that spacing. Q: Is there any way to keep my sweetgum (Liquidambar) trees from producing seed balls? A: Yes, but your timing will have to be perfect, and you'll have to interrupt the trees' natural growth cycle. To prevent the formation of gumballs, spray the tree with a blast of water in early spring just as it begins to bloom, assuming you can spot the inconspicuous flowers. Or spray the tree with a product called Florel. Q: I've heard that you can make pine trees bushier by pruning the candles. What are candles? A: The new spike-shaped growths on pine trees are called candles (figure C). By selectively removing the candles, you promote bushy growth. The easiest way to do this is to snip the candles in half.
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