It’s been a challenging year to be a shade tree here in North Texas.
That cold spell back in February did the unthinkable – it wrecked some of our finest trees. Native trees of species that have been growing here for centuries. You think to yourself, “Surely they’ve encountered weather like this before. How could this have done so much damage?”
For starters, this cold spell came really late in the winter. Plants were gearing up to leaf out or start blooming (or both). Old-timers would say, “the sap was up.” That makes a plant much more vulnerable to cold damage than it normally would be.
But the sealer to the whole deal was the depth and duration of that cold spell. Temperatures went way down, and they stayed way down there (sub-freezing) for several days.
“How cold it got” and “how long it stayed there” are the two factors that determine how much damage a cold spell might have done. This one did plenty.
Finally, it’s my own personal opinion that we’d gotten cocky. All this talk about “global warming” accompanied by 15 years of admittedly fairly warm winters (with a couple of exceptions thrown in) – we had shifted back to trees (and shrubs) that we had no business planting here in North Central Texas.
Humor me on this one: I still consider us to be in Hardiness Zone 7. I think the latest map did us a disservice by moving the boundaries northward so that we were shifted into the warmer Zone 8. We experienced a Zone 6 (much colder) winter this past February, and we’ve had three winters that were solid Zone 7s since the 2012 map made that shift. I still refer all my readers and listeners to the old USDA 1990 Hardiness Zone map.
Assessing where we are now
All of that is good to know, but where do we go from here? What can we do to save damaged trees? How can we tell which trees need to be taken down? Here are my steps to determining their vigor.
Look first at the trunk. Check closely for any signs of bark separation or visible vertical cracks (radial shakes). The phloem, a cylinder of tissue just inside the bark, carries manufactured sugars from the leaves down to the tree’s roots. If bark is lost, the phloem goes with it and the roots are impacted adversely. If the bark is lost all the way around the trunk, that’s a really bad sign for the roots. That tree is in very great jeopardy, regardless of how the canopy looks.
Step back 25 feet and look at the canopy. If it is filled with good leaf growth (and in the absence of bark splitting), your tree will probably be fine.
If the canopy is sparse with less than half of its leaves, that tree is probably running on borrowed time. If it has considerably less than half of its canopy, it’s definitely a candidate for removal.
If the tree has no leaves, or if it has very strong new growth coming up from its roots, the top has been lost. The original top needs to come down. You can opt to replace it with a new tree or you can train one of those shoots to be the new trunk.
Do not attempt to peel loose bark from your tree. Do not apply pruning sealant around or behind the loose bark. If there are jagged edges to the loose bark, and if they can carefully be removed by using a box-cutting knife, that would be fine, but do not worry about trying to get every last piece of loose wood trimmed away.
Addressing a few specific tree species, it appears to me that some 15 or 20 percent of our live oaks have been impacted. Of those, some have been lost, but many will recover. I would remove any dead branches that overhang anything that could be hurt or damaged should it fall in a winter storm. Otherwise, give them until spring to determine their condition.
Shumard red oaks were also hurt, again, I would say to the tune of 10 or 15 percent of the trees. Those that were impacted have generally lost their outer/top branches. Lower growth looks good, leaving dead branches sticking out of the tops of the trees like missed hairs in a haircut. Those branches need to be removed this fall.
Cedar elms and lacebark elms also suffered bark shakes and top loss. Some are completely dead without sprouts. They definitely need to be taken out soon. So do a few Chinese pistachios.
Many ash trees, Chinese tallows, loquats and even ornamental pears were brutalized by the cold. If they survived at all, they have rampant growth from their trunks or bases. These really need to be replaced with better species.
The final verdict in all of this ought to be an ISA certified arborist who has looked at the tree on site. These are well trained and highly skilled tree professionals. Be sure you’re hiring an insured company, and check out their references. Do not hire a company that knocks on your door. Between your valuable shade trees, your home, your car and your own safety, you have too much at stake to put it in the hands of an unproven person.