Avoid these common mistakes with shade trees in your North Texas landscape
Over a career of helping Texas homeowners with their landscapes and gardens, I’ve made mental notes of the crazy things we do with and to shade trees. I thought they might be worthy of a mention here this week in the hopes that I can help you avoid a few train wrecks in the future.
▪ Large trees in small landscapes. You see this all the time. A tree looks great in its 30-gallon pot at the nursery. It’s symmetrical, a perfect 12 feet tall and five feet wide. We plunk down our money and have it delivered and planted. But nobody tells us that our new live oak is going to grow to be 60 feet wide and 45 feet tall. No one told the HOA landscape committee that putting that tree on the “approved” list was a terrible mistake — that two of those in a modern-day urban front yard will soon shade out the lawn and most of the shrubs beneath it.
▪ Shade trees in parkways. Those are the little grassy strips between the sidewalk and curb. How much room do they give a tree to grow? Maybe four feet before it starts banging into the sides of buses and trucks. And do we really want to wall off our landscapes visually anyway? It’s better to plant our shade trees in the main part of the landscape and off to the sides so they can become a form of visual frame to the artwork we know as our house. It’s also better for the curb and the sidewalk since you won’t have surface roots there to push up the concrete.
▪ Tall trees beneath power lines. I really don’t understand this one. The mature heights of shade trees are plainly printed on nursery tags and in gardening references, yet people — even cities — continue to plant huge shade trees like bald cypresses, Shumard red oaks, live oaks, cedar elms and even Chinese pistachios directly beneath power lines. There is very little that destroys a tree’s good looks faster than a giant V-groove carved out of its middle or extended whacking of its wayward top growth once it starts to encroach into the wires. It’s especially egregious when we have to do that to a bald cypress tree.
▪ Line trimmers are arch enemies of our shade trees. It’s time for a tiny bit of high school biology/plant anatomy. Let’s start from the outside of a tree’s trunk. You have the bark, then the phloem, then the cambium and finally the xylem.
The phloem is a cylinder of cells that conduct sugars (manufactured in the leaves during photosynthesis) down to the root system. The cambium layer divides to produce more phloem cells to the outside and more xylem cells (the “wood” of the trunk) to the inside. Are you up with me, class?
If a line trimmer (or a dog chain, wire, or anything else) cuts completely through the bark, it’s probably going to damage the phloem and cambium, too. If that damage goes all the way around the trunk at any given level, the supply line down to the roots will be shut off and the roots will die. Eventually the entire plant will die and there won’t be anything you can do to stop it. That’s why it’s so important that you protect the bark on your trees’ trunk. Actually I prefer to taper my turf down to bare ground two to three inches from the trunk so that the trimmer never gets anywhere close to the bark.
▪ Root-feeding rods, plant food stakes and holes filled with fertilizer. These were the rage 35 or 40 years ago, but we have since realized that they put super-concentrated amounts of fertilizer near the points of insertion, while there was generally almost none being added just a few inches away. Since a tree’s roots are quite near the soil’s surface, it’s better to broadcast the fertilizer onto the ground and let the tree’s roots compete with your turfgrass. You’d be using a lawn food anyway (no “weed-and-feed,” please!), and timing would be the same for trees as for turf. Follow the feeding up with a deep soaking from your lawn sprinkler.
▪ Water bags around tree trunks. Really? A bag of water containing maybe a few gallons at the most and refilled every couple of weeks? At 100 degrees? When the tree may be three or four inches in diameter? Its important “feeder” roots aren’t going to be up by the trunk. They’re going to be out by the drip line. It’s better that you lay a much less expensive soaker hose around the drip line and let it run for 6 or 8 hours. A week later, lay it out again. Try to find a slightly different configuration for it.
▪ Trunks of Shumard red oaks, Chinquapin oaks, red maples, Chinese pistachios and other thin-barked trees exposed to full afternoon sun when they’re newly planted. That’s almost a guarantee of sun scald and subsequent lost bark. If it’s bad enough, and it often is, it can lead to the loss of the entire tree three or four years after planting. You must use tree wrap from the soil line up to the lowest branches, and it needs to be left in place for two years. This has been a very difficult message to impart, and thousands of trees have been lost in the interim.
▪ Improper use of pruning sealant. For the sake of brevity, I’m going to assume you know how to prune correctly. If not, do the research. But the question arises of whether you should finish the job with pruning paint. Foresters and arborists now suggest that we not apply sealant after we remove branches from our large shade trees. They contend that it actually delays healing.
The one critical exception is with oaks. All types of oaks must have pruning sealant on any cuts larger than 3/4-inch in diameter. It greatly lessens the chances of insects carrying the oak wilt fungus being attracted to the fresh wounds.
