When a Houseplant Gets Frosted

Standard
20171206A Dezidor, WC.jpg

Frost damaged aloe. Source: Dezidor, Wikimedia Commons

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.

However…

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

20171206B Maja Dumat, WC.jpg

Frost damage to an orchid leaf. Source: Maja Dumat, Wikimedia Commons

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

20171206D  The Seeded Gardener.jpg

Only lightly damaged by frost, this dracaena is now well on the way to recovery … other than for the damaged leaves you’d probably want to remove. Source: The Seeded Gardener

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!

20171206C Tim Burr, gardenerswood.com.jpeg

Remove any frost-damaged leaves. Source: Tim Burr, gardenersworld.com

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.

And wait.

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!20171206A Dezidor, WC

Advertisements

Houseplants Cringe at Sight of Snow

Standard
This is what 5 feet of snow looks like… from a plant's point of view.

This is what 5 feet of snow looks like… from a plant’s point of view.

I can’t help feeling my houseplants are angry with me. As the snow builds up all around them, they seem to be saying “What are you doing? Get rid of that white stuff! It’s cutting off my light!” In the photo you can see the side of the greenhouse as the snow builds up. What you can’t see is that the roof is entirely covered in snow and has been since November. What use is a glass roof if it lets in no light during the darkest days of the year?

Frost Damage to Houseplant

Standard
It took only a few seconds of extreme cold to damage the leaves of this Ficus elastica.

It took only a few seconds of extreme cold to damage the leaves of this Ficus elastica.

On January 25 2014, I blogged about moving my son’s houseplants from his place to mine at -20. I wondered at the time how they would fare after their (admittedly very short) exposure to such cold, dry air.

Well, 10 days later, all but one are doing fine. I even repotted two of them (they really needed it!), then repotted one of the two a second time after I accidentally knocked it over.

The one exception is a young Ficus elastica: one of those pots overcrowded with micro propagated cuttings that passes for a houseplant these days. It’s not that Ficus elastica is necessarily any less cold tolerant than the other houseplants, but it was the only plant that had not been fully covered. It was in a cloth bag with a  few other plants, but being taller then they, its upper leaves stuck out into the cold. I estimate that it was only exposed to about 30 seconds of cold air (in two blasts, moving into the car, then out of the car into my house), but now you can see the youngest leaves have browned along the edges and even their surface is damaged: a sort of yellowish mottling that might under other circumstances look like thrips damage, but that I figure is damage to the outer layer of leaf cells: the cuticle.

My guess is that these leaves will probably die and possibly also the bud at the plant’s tip. If they don’t, I’ll probably cut them off. However, the lower leaves (the ones that were inside the bag) seem fine. I’m assuming the plant itself is essentially all right and that it will soon begin to recover from its ordeal.

So, take my word on this, only a few seconds cold can damage plants: wrap them well before you move them in cold weather!

Moving Day

Standard
Mathieu's plant settle into my spare room.

Mathieu’s plant settle into my spare room.

It was brightly sunny and painfully cold (-20) when my son Mathieu and I moved his houseplants to my place yesterday. He’s moving to Montreal and wants me to care for his plants until he and his girlfriend find a permanent home. Not the kind of weather I would have chosen to put any plant outdoors!

I figured the car would have thawed out on the way over to his place (about 15 minutes from here), but the seats were still rock hard from the cold. I parked in total illegality in front of a fire hydrant, but with blinkers on: surely the cops would understand that we were moving incredibly delicate living beings than can’t stay outdoors more than a few minutes?

Mathieu had already packed the plants, covering them with black garbage bags. We raced them down the slippery steps and into my car. About 20 of them, of all sizes. Fortunately they all fit on the back seat. We simply dropped them off in my front hall upon arrival: I didn’t unwrap them until this morning.

How did they fare during the transition? I won’t know for a few days: my experience is that frosted houseplants often look fine at first, then the damage shows up later. Fingers crossed!

So, where to put them? At this time of the year, my place is jammed with houseplants and other overwintering vegetation. Also, I didn’t want to have to search for them throughout the house when Mathieu comes back for them. Finally, I decided to remove most of the plants from our spare bedroom, scattering them stuffing them in here and there throughout the house, then put all his in that one room. With a large, south-facing window, they should do fine. In fact, they should do better, as many of them are pretty light-starved. Let’s hope he finds a place with big, sunny windows!