With the arrival of cooler fall weather, gardeners need to be prepared for the threat of freezing temperatures and frost. If the weather dips below freezing (32° F or 0° C) or gets cold enough for frost to form, there’s a good chance that sensitive plants will be harmed or killed. Here’s what you need to know to make sure your plants survive the cold unscathed.
How plants respond to freezing weather
Different kinds of plants respond to the cold in different ways. Tropical and frost-tender plants are easily killed by freezing temperatures. While annuals also cannot survive a strong freeze, they release seeds to grow new plants when warm weather returns. The foliage of root-hardy perennials can be killed off during a freeze, however, the roots go dormant and survive until spring. With fully hardy perennials, shrubs and trees, the entire plant goes dormant to protect itself until spring.
Here’s how specific temperature ranges will impact plants:
Down to 28° F for a couple of hours: A light freeze or frost, this will likely just harm very sensitive plants as ice will only form outside the plant at worst.
Between 25-28° F for several hours: A hard/killing frost or moderate freeze, this will damage leaves and flowers, kill back root-hardy perennials and harm crops.
Below 25° F for several hours: a severe freeze, this will damage all but the most resilient plants.
The first and last frost dates provided in weather forecasts often refer to killing frosts. Most plants cannot recover from unprotected exposure to 28° F or below temperatures.
How to protect sensitive plants from frost and freezes
If a frost is in the forecast, it’s wise to take measures to protect your vulnerable plants. These include houseplants and tropical varieties, spring-blooming shrubs and trees, citrus trees, tender bulbs and tubers and warm weather vegetables and annuals. Below are several ways guard such plants from the cold.
Store indoors: Plants in containers can be moved inside, and tender bulbs and tubers can be dug up and kept in a cool, dry place.
Keep warm with water: Thoroughly watering plants before a cold snap can offer additional insulation and help protect plants from dying out in a freeze.
Put a cap on the cold: Tender sprouts can be covered overnight with upside down flower pots, buckets, cloches or even plastic milk jugs with the tops cut off. A layer of straw or mulch will also offer protection. Uncover the plants the next day once temperatures return above freezing.
Unfurl the fabric: To protect shrubs or trees, cover them with fabric, old bedsheets, burlap or horticultural frost cloths, using twine or clothespins to hold the material in place. Plastic sheeting is not recommended. To be most effective, use a frame to keep the fabric from touching the plants, and ensure the material reaches the ground to trap in the heat. Remove the coverings the following morning when the temperature is above freezing again.
For the best results, choose plants that are appropriate for your climate, or keep tender plants in containers that can be brought indoors. By keeping an eye on the weather forecast and protecting your plants accordingly, you can help ensure your garden handiwork isn’t blindsided by a frost or freeze.