When people hear the term “desert”, they often imagine an intensely hot, dry area, but I’d say those dramatically cold temperatures that recently seized Southern Nevada clearly demonstrated otherwise. When an area’s a desert, you can be certain only that the environment is dry, but it’s not necessarily hot. Antarctica, for instance, is technically the largest desert on the planet. Southern Nevada might have felt like an ice box, but it couldn’t compare with that!
For some local landscape plants, ‘though, the weather might as well have been arctic. Since freezing temperatures are relatively uncommon in the Las Vegas valley and its environs, it can be tempting to risk using plants that aren’t well suited for the extreme conditions here.
When temperatures are lower than 40 degrees, the most tender plants can develop something called “chilling injury”. These are varieties that aren’t well adapted to this area; they’d survive better in regions further south, like the Sonora Desert of southern Arizona.
A lot of the specimens that’re widely planted aren’t quite that fragile, but they’re not exactly “hardy” either. They may not suffer chilling injury, but they can’t tolerate freezing temperatures. They’re definitely going to experience harm on those rare occasions when it drops much below 30º. It’s a pity to see the damage that’s occurred in local landscapes already, and it’s going to be more pronounced by the end of winter.
Marginal plants can be killed in the desert cold; but even some of our most reliable ones can be damaged. Oleander, for instance; it’s tough. It can tolerate our conditions very well, most of the time. Even in the hottest summer sun, it’ll thrive and flower merrily. When temperatures stay well below freezing for several nights in a row, the leaves’ll become damaged and might appear to be diseased. The root system may be perfectly OK, but above ground, it looks pretty forlorn. Fortunately, when the shrub produces new foliage in the spring, it’ll more than likely look fine.
We all try to skirt around Mother Nature; including those of us who should know better.
I’ve had a lovely grouping of large aloe vera (that’s Aloe barbadensis) growing in my yard, and these plants were terrifically successful when we had mild winters for their first few years. Being from Africa, however, they’re neither native, nor terribly well adapted.
After a week of evenings and nights in the deep freeze, some of them have become flaccid and grey, as they’ve done in other bad winters. Because they were well established before the cold, the root system endured, and that will allow them to revive. I’ll have to remove the mushy center of the plants, so they don’t rot in the ground. There are probably thousands of local gardeners facing a similar situation – healthy plants that survived previous winters but now look like death.
At the Cooperative Extension office, we want to hear about these plants. Specifically, we’d like to know:
What kind of plant it was, and how long was it in its location. Was it protected by a wall or exposed to the wind? What direction did it face?
It’s also important to know if it was healthy before the freeze, properly watered and fertilized.
We’ll use this information to develop guidance for people, so there’ll be less of this heartache in future winters.
Happily, a plant may look as if it’s dead, but as long as it has a robust root system there’s a fair chance that it has survived and will return. If you can avoid removing it until well into the spring, you might have a happy surprise.
For the rest of this winter, try protecting that root system by keeping mulch on the soil. A layer of bark, chipped wood, or even straw helps moderate soil temperatures, and that can make a difference in plant survival.
Let me remind you - I’ll be offering an expanded “Growing in Small Places” series in 2014, with the first class on Pruning in January. Call the Master Gardener Help Line for details.
For KNPR’s Desert Bloom, this is Dr. Angela O’Callaghan of the University of Nevada Cooperative Extension.