A desert freeze?
Yes, many regions of the desert do have freezing winters.
In layperson terms, we talk about three levels of the desert. The high desert of Albuquerque and other similar cities is at 5,500 feet above sea level. These areas will have a winter typical of more northern climates with temperatures below freezing much of the season. The low desert such as Phoenix, Arizona and Palm Springs, California rarely has freezes, but it does happen. The elevations range from 200 feet to almost 2,000 feet.
Middle desert regions such as Tucson, Arizona, with elevations from 2,000 – 4,000 feet experience different levels of below-freezing temperatures. In the past ten years, there have been short-lived freezes and drastic experiences with days where the temperatures hardly reached 40°F and the damage to plants was catastrophic.
Of course, our desert’s first freezes will come right when you are in the chaos of holiday preparations. Therefore, the best bet is to get your freeze protection materials ready before any danger is in sight. Target date: November 1.
Hard Freezes and Microclimates
Desert Dwellers often will panic when word of a hard freeze is forecasted. A hard freeze is when it is cold enough that vegetation will be damaged and ice will form in standing water. In the U.S., a hard freeze is 27°F. There are microclimates around your home that can have different temperatures. If you are on a wash, you will have colder airflow. If you are at a higher elevation than the valley floor, you will experience colder temperatures.
It is a good idea to invest in an electronic thermometer and place the gauges around various areas so that you can see what your temperatures are in relation to the airport temperature because that is where the forecast is taken. Then you will know if the airport is predicted to be 35°F and you are typically warmer than the airport, your plants should be fine. However, remember that your tropical plants need to come inside or be well protected when temperatures get to 45°F.
Remember that plants grown in pots will be more sensitive to the cold by several degrees than those grown in the ground.
Don’t prune after mid-October
When you prune a plant, the action stimulates new growth, which is more susceptible to freeze as these shoots are more tender.
The average first freeze in the middle desert is November 15th. I suggest you don’t prune after mid-October and then hold off on pruning frost tender plants until after the danger of freeze is past.
Materials for Plant Protection
Gather your materials. You can choose from various methods to protect your plants.
In the perfect world, you would have your tender potted plantings on pot dollies. Then wheel them to a protected area such as:
- Close to the warmest side of the house under a ramada
- Into a garage
- Under the carport
To cover your tender plants, here are the materials I recommend:
Frost cloths, sheets, lightweight blankets
Frost cloths come in large sheets. Take the time to cut pieces for each pot. I recommend you cover each one individually so that air does not seep up under a widely spread cloth.
Cut the cloth large enough to drape over the entire plant and be tucked inside the pot, weighted down over the soil with rocks.
Label the cloth with the pot’s style or number your pots on a map and label accordingly.
Fasten ends together with clothespins so that the wind cannot open the covering.
Cover your plants before the sun goes down. Leave the covers on until the sun heats the earth and pots and the temperatures rise above 40°F.
On the rare occasion that the temperatures do not rise above 40°F, you may leave the covers on for a couple of days. Don’t succumb to the sense that they are better off covered for more days than that because you will need to check for the moisture level and let them breathe. I know daily recovering can be a pain in the neck, but it’s your investment in your garden that you are protecting.
Do Not use towels, heavy spreads or plastic of any nature
Towels, spreads, blankets or comforters are not recommended because if it rains, they will become sodden and cumbersome and could break the branches of your plants.
Never Use Plastic
Do not use any plastic or bubble wrappings for any plants. The plastic gets cold and will freeze the plants it touches. It will not retain heat.
Clothespins, as mentioned above, will keep your cloth tightly snuggled around your plants.
Rocks should be placed on the cloths inside the pot, creating a base for the cocoon you are creating.
Sharpie Pen – to mark your frost cloths with the pot number making recovering each year easier.
You can use heat casting lamps under a cover to add additional warmth to your planting. Use outdoor fixtures and be sure the lamp is not touching anything flammable. I recommend you use some stakes to hold the cloth up off the plants and light, allowing some air circulation.
Giant Styrofoam Cups for pillar cactus
Columnar cactus grow from the tips of the plants. Therefore this is the area you want to protect. Styrofoam (not plastic) cups are perfect for this, but you have to make sure you are able to get the appropriate size. Most often, I have found that they need the jumbo cup size or Slurpy.
Newspaper and paper or plastic* grocery bags
If you cannot find styrofoam cups of the right size or are caught unaware, take newspaper and wad it up, wrapping it around the crown of the cactus. Then take a paper or plastic grocery bag (*note – the ONE use for plastic allowed) and tie the bottom around the stem of the cactus. If using plastic, make sure it is not directly touching the stem but that there is some newspaper between the cactus and the bat.
Google Your Weather
A terrific resource is the US Weather Service. Click here for the Facebook page for Tucson. For other locales, change the name to your city or closest one and you will come up with different options.
The definition used by the National Weather Service to meet their criteria for a Freeze Warning is as follows:
A Freeze Warning is issued when significant, widespread freezing temperatures are expected.
Hard Freeze Warning – Widespread temperatures at or below 28 °F (−2 °C) during the growing season. A hard freeze may occur with or without frost.
It’s Up to You
You have to decide what your level of risk acceptance is. Just like in your investments, if you are unwilling to risk your plants, cover sooner rather than later. Another option is to grow as many cold hardy plants as possible. However, if there is a severe freeze over a longer period of time, even these plants will be at high risk. If you were in the southwest in the winter of 2007, you know how bad it can be. There was not much that could be done other than taking plants inside. Certainly, something the desert community is not expecting.