Spring presents the looming threat of early-season freezes and frosts in the high country. The last frost date for our zone is May 13th, and we expect to have unexpected cold snaps during the spring months. Therefore, it's best to protect and prepare tender plants if and when these threats arrive. Here's what you need to know.
What is the weather predicting?
The temperature and time of cold weather are two main factors that can damage plants.A freeze presents more damage than a light frost as colder temperatures over a longer period of time are more damaging than a short stint of weather in freezing temperatures. Here are some important weather terminology to consider:
Frost Advisory - Temperature is expected to fall to 36 degrees to 32 degrees Fahrenheit.
Freeze Warning - There is at least an 80% chance that the temperature will hit 32 degrees Fahrenheit or lower.
Light Freeze - 29° to 32° Fahrenheit (can kill tender plants)
Moderate Freeze - 25° to 28° Fahrenheit (can be destructive to most vegetation)
Severe or Hard Freeze - 25° Fahrenheit and colder (can cause heavy damage to most plants)
Frost comes straight down (like a blanket), so covering plants is an excellent preventative measure. Move plants in containers or unplanted varieties underneath a table or roof to protect them from frost. If your plants are in the ground or unable to be moved undercover, use a breathable fabric such as burlap or a bedsheet to drape over plants to protect the new growth. Do not use plastic or a material that will stop air movement to the plants. If you cannot cover your plants, hose them off the morning of the frost before the sun hits them. The sun hitting the frosted leaves is what is damaging to the plant or new growth.
What should I do if I wake up to a frost? If annuals experience frost, pinch them back, and they should recover. Likewise, if perennials experience frost, they should return from their established root systems over time.
If a freeze is in the weather prediction, water plants before the freeze. Well-hydrated plants have a better success rate undergoing cold weather. Bring tender plants inside out of the cold or into a protected area. If plants are in the ground, cover them like you would during a frost with a breathable fabric or material. If possible, keep air between the plants and the cover using a structure or frame, then remove the cover the following morning.