Normally, you shouldn’t expose houseplants to frost. The vast majority are tropical plants, incapable of supporting even light freezes. And even the few houseplants of subtropical origin, theoretically capable of taking a few degrees below freezing under certain circumstances, will be damaged if the frost persists too long. I always recommend bringing in houseplants at summer’s end, wherever that is in your region, not even waiting until early fall. When indoor and outdoor temperatures and humidity levels are about equal, the transition is soooo much easier! That way, there’ll be no shock or leaf loss when the plant comes back indoors, nor risk of frost.
We all make mistakes. Maybe you were very busy at summer’s end and delayed bringing plants indoors. Or you were away for a while and frost came early. Or (and this has happened to me more than once), you thought you had brought all your plants in, and only realized you missed one or two after frost had hit.
And sometimes frost damage can occur indoors as well. I live in a very cold climate and one winter we lost power for three full days … while we were out of town. We didn’t even know until we got home and saw the damage. I lost all my houseplants but two! (One was a clivia that looked fully dead, yet resprouted from the base many months later. I still have it!)
The Damage Frost Does
Frost causes devastating damage to plant cells. As water freezes, it expands, causing cells to burst open. Then when temperatures warm up, they suffer further damage through dehydration. Young cells are the most fragile, thus young leaves, flowers and flower buds suffer the worst damage. More mature cells can take a bit more cold … or at least, longer stretches of it. Deadly cold extends right through thin stems, but takes a longer time working its way through thicker ones … and bark, when present, can make a fairly good insulator. Therefore, where there is life after frost, it tends to be on the inner (thus less exposed), older branches … and at the base of the plant.
House plants capable of regenerating from their base, their roots or underground rhizomes, bulbs or tubers are the most likely to recover from frost. Soil tends to hold on to heat. It can take days or weeks for the ground to freeze even when there are nightly frosts.
Frost damage is most often seen by leaf edges or tips (very light frost) or entire leaves (heavier frost) turning brown, black or soggy, sometimes dropping off, sometimes drying up. Flowers and flower buds react similarly. Leaves on the inner and lower parts of the plant may remain intact, especially if there was little wind. Soft stems turn brown or black and may curl down, turn mushy or even collapse; tougher ones may show no other sign of damage than that they are now leafless.
All May Not Be Lost
Don’t automatically give up on a houseplant that has suffered frost damage. There may be dormant buds under the bark or at or below the soil level. Recovery can be slow, though: new growth may take months to appear and the plant may take years to reach its former size. You have to decide whether you’re willing to wait or prefer starting over with new plants.
If one of your houseplants has suffered frost damage, get it indoors as soon as possible. Don’t worry about acclimatizing it: get it out of the cold fast!
Cut back damaged leaves and any obviously dead growth. If it’s a shrubby plant, you might as well prune it back heavily, shortening the trunk and main and branches: that will give it a fuller look … if it recovers.
Put the plant in a room heated to normal room temperatures, with moderate to high humidity and in reasonable light. Keep the soil slightly moist, checking occasionally.
It can take months before signs of life return. And unfortunately, sometimes the plant starts to produce new growth and you think you’ve saved it, then it suddenly dies: the damage was just too severe. Usually, though, if green growth appears, the plant will recover and will become a happy, healthy, functional houseplant again.
Just don’t let it suffer frost ever again!