Protecting Plants Against a Freeze
Most native plants will tolerate a light frost once they have become established (about a year after installation). If you have newly installed plants, you will want to protect your plants in a hard freeze. Even native and adapted plants could even be affected by temps below 32 degrees. Signs of freeze damage are: tender new growth and even evergreen leaves will wilt and turn brown. (The plant in the above image is a phenomenon called a frost flower, when the sap of a plant expands).
Since the roots will be exposed to the dropping temperature more so than those protected by soil, you’ll either need to cover or bring these plants inside until it’s back above freezing. Even wrapping the pot or covering a cluster of pots will help protect them. Pro tip: old-school halogen (not LED!) holiday lights put off a small amount of heat and help keep the temp under a sheet up a few degrees.
Water Prior to a Freeze
Wet soil holds heat in better than dry soil. Dry air can parch leaves, and watering the roots before a freeze and so that it can act like an insulator and keep the heat at the base. Ice forming can even keep heat in the roots. Remember to water at the base, and not the leaves – so running drip irrigation as early in the day as possible will work great. This is true for most plants unless they have fleshly leaves like agaves and succulents – only water those plants lightly.
Covering a Planting Bed
Old sheets, burlap, or moving blankets draped over plants will be better than nothing when temps drop into the low 20s or teens in Austin. Even better, hammer in stakes or create a PVC frame to bring the cover off the plant and add more of a barrier between it and the frigid air. The San Pedro Cactus (pictured above) will even be protected by styrofoam cups on the tops of each plant.
DIY Hoop Covers*
*Originally shared on a blog post from Nov. 26, 2013
My mother lives in the hill country and they get a deeper freeze out there, so she covers her plants just to be safe. I asked her to send pictures of her burlap dome (also known as hoop covers) set up to share here on the OES blog.
Burlap in a roll (can be found at Home Depot or online)
Big binder clips
Twine or paracord
12" of 1/2" rebar (4 per dome - depending on overall size)
3/4" PVC pipe (to fit over the rebar - test to make sure you're getting a good fit )
Orange caps (to fit over rebar when not in use)
Drive rebar into the ground in the four points of a square, around a shrub or a small group of plants. (Or you can make a larger set up like the featured image.)
Place PVC pipe over the male end of the rebar and cross over plant. Do this with another PVC pipe to make a dome like a tent.
Drape burlap over the dome. Clip in place until edges are sewn together with twine.
Use clips to keep burlap dome over PVC in the wind.
While not in use, place orange plastic caps over rebar in the ground for safety. Remove rebar at the end of the winter season. You don't have to take down PVC domes during the week if a frost is not over. Remember to roll up burlap during the day if it's above freezing so plants can get sunshine and tie it up on top with paracord.
What's nice about the burlap is that water and some sunlight, as I just mentioned, can still permeate through to feed the plants. I like the dome idea to keep ice from hurting plant branches and leaves. It's labor-intensive to create at first, but it makes protecting your plants the rest of the season easier (and from year to year during deep freezes once native plants are established).