Most houseplants require warmth year-round and will suffer damage if exposed to cold. Signs of damage include rubbery or wrinkled foliage, wilting, discoloration and poor growth, as well as more serious issues such as rot and blackened stems. Preventing freeze damage is best, but affected houseplants can be revived if you give them the right care.
Hardiness and Temperatures
Most houseplants come from subtropical or tropical climates where temperatures stay fairly stable year-round, although some hail from temperate areas and will tolerate some cold. Species such as the corn plant (Dracaena fragrans) grow outdoors in frost-free climates of U.S. Department of Agriculture plant hardiness zones 10 through 12 and will suffer cold damage at temperatures below 50 degrees Fahrenheit, while Dutchman’s pipe (Aristolochia macrophylla) will survive outdoors in USDA zones 4 through 8 and can tolerate below-freezing temperatures.
In most cases, daytime temperatures between 65 and 75 F and nighttime temperatures above 55 F will provide the right conditions for growth with minimal risk of damage.
Reviving houseplants after cold damage is simple to do and requires minimal effort. The key is to slowly acclimate the plants back to normal conditions. Too much water, warmth and light too soon can increase damage to the plant, so:
- Shield the plant from direct sun and high temperatures. Indirect morning light is fine, just keep the plant protected from strong midday sun.
- Don't water it. Keep the soil dry until the plant sends up new growth, then water lightly for a few weeks before resuming the plant’s normal watering schedule. Do not let the soil become soggy.
- Increase the humidity around the plant. Move it to the bathroom or other naturally warm, humid environment or place it on a tray of wet rocks to increase humidity around the leaves.
- Prune the plant sparingly. Remove any damaged leaves 1 to 2 inches below the damaged area using sharp pruning shears. Soak the shears in a solution of half rubbing alcohol and half water for five minutes before use to sanitize the blades.
If more than one-half of the plant is damaged, it may not survive. Throw out the plant if more damaged growth appears after treatment, if the treated areas begin to rot and produce a foul odor, or if no new growth appears in spring.
Fertilize the plant lightly with a weak solution of 1/4 teaspoon 20-20-20 fertilizer diluted in 1 quart of water. Apply the solution to moist soil every week, starting in spring.
Preventing Freeze Damage
The temperature requirements for houseplants vary among species and cultivars, but a few basic tips will help prevent freeze damage on all but the most sensitive types.
- Grow houseplants in a room with south-facing windows because the all-day sun will keep the area warmer. Avoid north-facing windows, which are colder.
- Do not position houseplants on windowsills or near windows in winter, even if the panes are covered with curtains. Cold radiates out from windowpanes, which can damage houseplants. Do not let the leaves touch the glass.
- If you're sunning houseplants outdoors during warm summer weather, move them indoors well before temperatures dip below 55 F.
- Maintain moderate humidity around the plants. Moist air holds more heat, so keeping the air on the humid side may keep temperatures high enough to prevent cold damage. Place the plant on a tray of moist pebbles, or mist it daily to keep the leaves moist.
When transporting houseplants home in winter, cover them with a paper bag or cloth and place them in the front seat of your car near the heater vent to keep them warm until you get them home.