Protect your plants: Recognize the signs a frost or freeze is on the way

Posted at 2:23 PM, Oct 05, 2018
and last updated 2019-04-26 16:28:03-04

COLORADO – If you have flowers, delicate plants, or even a full garden you are probably aware of staying on top of potentially frosty overnight temperatures.  This is the time of year when the first frosts and freezes occur.

Short of knowing the forecast, here are some tips on how to pay attention to clues during the day for insight on what may or may not happen that night.

Just for reference, the average first frost in Colorado Springs is October 1st, while the first snow averages the 3rd week of October.  In Pueblo, the first frost average date is October 8th, and first flakes of snow typically fall in the first week of November.

Find more information the average date of first fall freeze on the National Weather Service site.

Now, to those clues on what to look for:

  1. If daytime temperatures reached 75F or more, it is unlikely they will fall to frost-worthy readings at night. (Caveat, because southern Colorado is an arid climate, it is possible for wide temperature variations, of over 40 degrees from day to night, with a clear sky. So this “rule-of-thumb” is not quite as reliable as for more humid climates.)
  2. Is it breezy? Winds at night keep air from settling and cooling as much (unless that wind is related to a cold air mass pushing in.)
  3. Is it cloudy? Cloud cover acts a little like a blanket, holding in heat of the day. It is when skies are clear at night, that “radiational cooling” is maximized…meaning that the day’s radiation is allowed to radiate back into space at night.
  4. What is the current dew point? The dew point is the temperature at which, once reached, the air condenses with moisture. So, if the dew point during the evening weather report is 45F or above, you’re probably safe. If under 40F, you’re at risk, pending the above.
  5. What is your garden’s elevation relative to the neighborhood or the rest of town? If you are on a bit of a slope, the risk for frost is less, as cool air pools into the valleys, at night.
  6. How tall are your plants? Plants nearer to the ground stand a better chance of surviving because they are nearer the earth, which radiates heat at night. Also, taller plants nearby may protect them a few degrees, too.
  7. Are you in a city or rural area? Cities create an “Urban Heat Island” effect. The buildings and concrete are absorbers of the sun’s heat. Also, buildings generate heat. So, between the two, nights in the city are anywhere from 3-15 degrees warmer than surrounding rural areas, as they slowly release the captured heat of the day.

If you feel a frost is possible, you can use the sprinkler to periodically water the plants at night. Water is harder to freeze than air, plus even if a film of water freezes on plants, it keeps them from going any lower than 32F.

Further protect your tender plants with frost blankets, burlap, cloth, old towels, or even bed sheets to insulate them.  Do not use plastic sheeting as it traps in moisture which can freeze. For best results get everything covered before sunset.

To keep up with the weather year-round, bookmark for the latest from the First Alert 5 Weather team.   You can also keep track of the forecast, watches, and warnings with the First Alert 5 app.