Caution! Hard Freeze! 🥶

With the forecasted winter freeze here in Austin, we wanted to share some tips for protecting your outdoor plants.

Snow piles up on this East Austin home
Austin received 6.4" of snow during the unprecedented and historical eight-day winter storm last year

First, let's learn the difference in these terms as defined by The National Weather Service: Frost, Freeze, and Hard Freeze.

  • "Frost" forms when solid surfaces are cooled below the dew point, typically 33-36°, where light winds can initiate frost formation if the humidity is high enough.

  • Freeze” occurs when the temperature is 32° or lower, resulting in significant damage to unprotected plants if temperature remains at-or-below freezing for several hours.

  • A “hard freeze” occurs when the temperature drops to 28° or below for at least a few consecutive hours which may destroy seasonal vegetation and many types of plants.

 

The Winter Storm Watch issued for Austin and San Antonio from late Wednesday through Thursday afternoon will bring in the potential of freezing rain and sleet, ice accumulation, and—along with it—a hard freeze.


For protecting plants from this hard freeze condition:

  • Water *before* the freeze (avoid the leaves) as you should avoid watering during a hard freeze. Water helps soil hold warmth and plants need water to counter wind that may dry them out. The Farmers' Almanac teaches us that moist soil can hold up to four times more heat than a day soil, conducting heat faster to the soil surface, and keeps the air above it about 5° warmer so water well before a frost.

  • Bring potted plants inside. Move them into a garage, if possible, or covered porch until the freeze passes. Container plants are the most susceptible to cold weather, the soil in the planter gets almost as cold as the air temperature. Make sure to bring any tropicals *inside* the home as these are most vulnerable.

  • In the early evening, drape plants loosely with frost cloth which can be found locally at hardware stores. Less effective materials, but still helpful, are bed sheets/towels/blankets/painter’s drop cloths/burlap and the like; use overturned coolers, buckets, or boxes. Anchor your coverings with rocks, bricks, or stakes to prevent sheets/blankets from blowing away or shifting position. Plant coverings should extend all the way to the ground which creates an air pocket that assists in trapping heat inside this temporary shelter. For the best protection, use a frame to prevent coverings from touching the plants. Avoid plastic garbage bags, if you can, as this material can trap moisture and/or not allow the plant enough oxygen to breathe — if this is your only option, make sure the plastic is not touching the plant. Be sure to remove coverings mid-morning so that the sun can warm up your plants. If you do not remove coverings, condensation can build up and freeze again under the covering, damaging the plant.

  • Check for cracks in the soil surrounding vegetation that could allow cold air to penetrate into the root zone; correct the cracks by filling these areas with soil.

  • Insulate plant roots, newly planted trees/shrubs, and garden beds with mulch.

  • During a temporary cold snap, cover entire shrubs or wrap with burlap, sheets or blankets for insulation. As with the above covering suggestion, be sure to extend the cover all the way down to the earth to retain heat and, for best results, create a frame to cover the foliage.

 

Special consideration:

Native plants, which are those plants that have naturally occurred in a particular region without human introduction, tend to be able to handle historical climates. However, during these atypical weather patterns, we must remain mindful of these record lows that hang around for extended number of hours/days and take special care accordingly. Newly planted natives might not be sufficiently established to be able to survive these conditions.

Check out our previous post Protecting Plants Against a Freeze for more details.


Have a tip about protecting your plants? We love learning new things, please share your advice with us!

 

Bibliography:


National Weather Service. “Frost/Freeze Info.” Weather.gov (blog), 2021, /gid/fallfrostfreeze


Almanac. “Protecting Your Garden From Frost.” Almanac.com (blog), October 21, 2021, /protecting-your-garden-frost