protect your plants from hard freezes

In the desert southwest, cold weather usually arrives around Thanksgiving, with the first hard freeze occurring either late November, or in some cases, after Christmas. If you have frost tender plants, it pays to be prepared before that first freeze hits.

If you’ve been reading my articles about “right plant; right spot” and have paid attention by purchasing cold tolerant species, then you probably don’t have to worry. For the Tucson area, look for plants hardy to at least 15 degrees. For Green Valley and other areas around 3000 feet in elevation, look for cold hardiness to 10 degrees or colder. You can probably skate by with cold hardiness to 15 degrees, but be prepared to cover plants in severe cases.

Plants that need to be covered include all of those exotic cactus and succulents you purchased at your local nursery. Chances are pretty good they are from parts of the world where temperatures rarely go below freezing. Also be prepared to cover citrus. Plants not to bother to cover since they are meant to go winter dormant here are lantana, bougainvillea, queen’s wreath and red bird of paradise, to mention a few.

Proper covering materials do not have to be special “frost blankets” for which you will pay a high price. It’s also important to understand that these specialty covers usually only protect to 22 degrees.

Old sheets and blankets work just fine. Never use plastic, which conducts cold to the plant, or burlap, which doesn’t hold in heat. When you cover, make sure the cloth covers the entire canopy all the way to the ground, and then some. What you are trying to do is capture heat radiating from the ground, not protect the leaves from cold temperatures. Secure the cover to the ground with heavy rocks, stakes or pins, since a cold storm often includes high winds. For many plants, including citrus, a blanket is not enough. You will also need lights underneath the blanket. The old type of Christmas tree lights, the ones where the bulbs generated a lot of heat, are perfect, but not available unless you still have some. Do not use mini-lights or led high bay light , since neither of those generate heat. The next best thing to old Christmas lights are mechanics drop-lights and a 75 watt bulb. Depending on the size of the tree, you may need more than one. Hang in the lower branches, being careful not to let the bulb touch the bark.

The practice of putting Styrofoam cups over columnar cactus does not protect the lower part of the cactus from freezing. You can use the cups to prevent thorns from getting caught in the covers, but it’s best not to rely just on the cups by themselves.

Two other important factors to keep in mind are to make sure your plants with plant grow lights are well-hydrated. Drought-stressed plants are more prone to frost damage. Also you need to remove the covers every day! Never, ever, leave them on for days, weeks, or in some cases as I’ve seen, months. The plants need sunlight to thrive. Additionally, since you are trying to capture warmth from the soil, removing the covers allows the sun to warm up the soil again in anticipation of another cold night.