You’ll find tons of variety available in Phoenix landscaping plants, but not all of them are hardy if it gets too cold. Never use weather averages to determine if you’ve found a winter hardy plant that will look great through all seasons here in the valley. Why? Because ‘averages’ don’t take real possibilities into account. Nor do they cover the oddities that take place in different micro climates around the area.
What’s A Micro Climate?
It can exist in your yard, in a single neighborhood, or even cover a section of your city. They are conditions that are different in one particular spot than those all around them. Take a low spot or valley for instance, where fog always forms in wet weather when the ground and air temperatures are opposites, causing vapor to form. It doesn’t happen when it’s dry, the moisture must be in the ground for the clouds to rise. Consider the difference in temperature on the south wall of your house compared to the north wall, this too is a micro climate, and plants growing close to the heat or cool radiating surfaces are affected by what that oddity does to their living space.
While we have heat waves and cold snaps depending on the season, some micro climates create a situation that can damage ‘winter hardy’ plants sold for Phoenix landscaping. They are usually hot or cold hardy, but not always. It all depends on where you plant each one and what weather extremities happen along. In winter, the biggest problem is whether the plant is frost hardy or frost sensitive, but there are times that conditions drive the air temperature below 20°F. This is way to cold from some plants commonly used in Phoenix landscaping. Often they recover from this extreme exposure, though the plant’s beauty and stature will suffer for a while. There are, however, ways to avoid the worst of winter damages.
Cold Settles, Heat Rises
Elevation has big influence on the possibility of frost damage. If you live in a low area, frost will form faster in your yard than it will on higher ground. And there can be certain spots in your yard that cold damage appears on plants before anywhere else. Of course, once the temperature drops below 32°F, frost isn’t spotty – it’s everywhere. However, it lingers in depressions in the terrain longer than it does in higher elevations… because cold settles, and heat rises.
Frost always damages plants that get morning sun first. Except for those really sensitive to frost specimens you might have planted, anything growing in the yard that is in shadow until later in the day generally goes through frost unscathed. It’s the sun hitting all those little ice crystals that causes a lot of early frost damage, because they act like an army of magnifying glasses. The effect is no different than what happens to a piece of paper in the same situation.
The smaller it is, the faster damage repair. Not the plant’s size when freezing temperatures descend, but it’s mature size and structure. Don’t gamble with trees. They’re the largest and slowest growing of all the plants in a yard. So, when disfigured, they detract from your entire landscape, and are the hardest to restore to original glory.
Stick to natives or trees known for acclimating to our harsh desert climate really well. These will be the least likely to suffer severe damages from those occasional cold snaps we have from time to time:
- Palo Verdes
- Chinese Pistache
- Evergreen Elms
Growing out of frost damage is much easier for shrubs, subshrubs, perennials, vines, and grasses – as long as they’ve been in your yard for over a year. The reason has to do with depth of their root system. Because if the root ball escapes frost damage, chances are with some patience it’s only temporary damage. Some plants will reproduce themselves even if everything above the soil freezes to death.
Now, if it’s newly planted, you might want to cover it when the weatherman says frost is possible. Perennials and grasses damaged by a surprise dip into the freezing zone are nothing to get excited about. Just cut them back to a 3-4″ tall, and in spring a much nicer plant will appear than what you lost. These are small players in your overall landscaping, and the wisest ones to take big chances on. At least, that is, if the species will deal with our intense summer sun and temps.
Some subshrubs easily fall into the perennial category. Others will be more shrub-like in how damage should be treated. Chances are with some educated trimming of the frost killed parts only, they’ll rebound quickly once warm weather returns in spring. There is no general rule of thumb. It varies by type and species. But they will all bounce back better and more willingly if planted long enough to develop a good root system. Just one more reason to make sure you’ve got the best watering practices for each plant type in your yard. Good water and fertilizer availability to fit the plant’s needs has a lot to do with how vigorous it’s root system is, which in turn influences new growth.
Study Your Micro Climate
As we head into mid-December pay attention to how the cold affects different parts of your Phoenix landscaping. In a few weeks, nighttime temps below 30°F are very possible. Keep an eye on what happens on the east side of the house versus the west and north. Note the difference in your plant’s reaction growing close to the house versus out in the open. In fact, if you really study your yard over an entire calendar year, taking notes on how different extremes affect plants in the various areas from one season to the next, it gets a lot easier to know when to gamble on plant selection, and where you really should play it safe.