The Garden Guru: Let’s talk trees

Posted Saturday, Jul. 20, 2013  comments  Print Reprints

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There’s no better time to measure the real impact that shade trees have on our surroundings than in the middle of another hot Texas summer. Next time you wait for a bus or a taxi, try standing out in the sun. You’ll be grateful for shade when you find it.

But like most consumer items, not all shade trees are equal in terms of quality and length of service. With trees, it’s “buyer beware,” and this is the season when you can really see why. Here are a few thoughts I’ve gathered over 40-plus years of answering North Texans’ gardening questions.

Faster isn’t better

Fast growth is a terrible criterion in choosing a new shade tree. Sure, you want shade as quickly as you can get it. But are you willing to sacrifice good looks, pest resistance, longevity and site adaptability in the process? As soon as you move past that need for speed, your gardening life will become a lot easier. Choose first for quality.

If you absolutely have to have shade as quickly as possible, you can still accomplish it by buying a larger container-grown or balled-and-burlapped specimen. Nurseries offer trees in all sizes. Every time you step up to the next larger tree size, you’ll be saving yourself a year or two of waiting for shade.

Fall is the best time for planting, so do a little preparatory browsing in nurseries now. Some nurseries will even hold the tree for you until fall for a down payment on its purchase. Often, trees go on sale as summer winds down. That will let you buy a larger tree for the same dollars, and that translates into shade a year or two sooner.

Measure twice, plant once

Choose a tree species that fits the space you have available for it. It’s always amazing that cities allow developers to plant tall trees (red oaks, cedar elms, bald cypress) beneath power lines, or that they permit spreading trees (as in live oaks) to be planted in parkways adjacent to streets. Similarly, you don’t want to plant trees where their branches will rub against the eaves and roof of your house. Stay 15 or 20 feet out and you’ll save yourself a lot of heartburn years later.

Tree roots can be a problem. They’ll raise driveways, sidewalks and patios, and they can do serious damage to foundations. Roots grow toward moisture, and it’s always moist beneath a concrete slab. If tree roots are threatening your house, an arborist can install a root barrier a few feet out from the foundation or drive. Fall is the best time to do so, once the tree’s most urgent calls for water have passed.

Cause for concern?

Many species of shade trees begin to drop leaves by mid-summer. That’s certainly true of the large-leafed, fast-growing types like fruitless mulberries, cottonwoods, silver maples and catalpas. If you have one of those trees, and if that’s what you’re seeing, it’s usually nothing to be concerned about. Those trees have so much cumulative surface area in their leaves that they can’t pull water into their vascular systems fast enough.

Older internal leaves start to shed no matter how often or how much you water the trees. They’re jettisoning some of their responsibility by shedding large leaves. It’s not uncommon for these fast-growing types to drop as many as a third of their leaves in late July and August.

Water well

Wondering how best to water your trees? Soaker hoses and drip irrigation lines saturate the soil with almost no loss to evaporation. Form a large doughnut coil around the tree’s drip line (outer canopy of leaves). That’s where the most active small “feeder” roots always will be, and they’ll be in the top 6 to 10 inches of the soil. Let the drip lines run slowly overnight.

You can protect a valuable shade tree by soaking the soil deeply and thoroughly as few as four or five times per summer. And those same hoses can then be used to keep shrubs and groundcovers going as well.

Pests or predators?

Woodpeckers and sapsuckers drill holes into the trunks of oaks, pecans and large hollies, among others. The holes will be in horizontal rows, as opposed to the random arrangement of tree borers. The birds do little or no permanent damage. They’re pretty much a “no call to action” item.

If you’re seeing tiny “driplets” of water falling from oaks, elms, pecans and even crape myrtles, you either have aphids or scale insects that are secreting the honeydew. Soon, black sooty mold will start to develop in the honeydew. Use a systemic insecticide to control the insects, and the sooty mold will take care of itself.

If you have a pecan or live oak that has developed random dead branches within its canopy, odds are that it’s home to several squirrels. They sharpen their teeth by chewing on tree bark. Since they’re already in the oaks and pecans waiting to harvest the acorns and nuts, they take out most of their damage on these particular species. There’s not much you can do to eliminate them, but the good news is that their damage is seldom of much concern.

Neil Sperry publishes “Gardens” magazine and hosts “Texas Gardening” from 8 to 11 a.m. Sundays on WBAP AM/FM. Reach him during those hours at 800-288-9227 or 214-787-1820.

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