As I live in the Pacific Northwest which is not the right climate for growing many types of cacti in the landscape, I keep mine as houseplants.
But I like to let them spend the summer outside, hanging out on the porch or patio basking in the sun.
One year, I kind of, sort of forgot about my plants on the side patio – a case of out of sight out of mind.
It was only when I heard the news anchors talking about how the recent freeze had destroyed some late-season crops in the area that it hit me: My cacti were out there, fully exposed to the elements.
We link to vendors to help you find relevant products. If you buy from one of our links, we may earn a commission.
I headed outside to find most of them looking okay, while a few had suspicious white spots. I brought them all in and started the process of triage and rescue.
If you’ve ever been in a similar situation, you know the heart-stopping sense of dread when you realize that your tender houseplants have been left out in the cold. Maybe you’re experiencing it now!
On the bright side, cacti are pretty good at repairing damaged tissue, so don’t immediately assume that your plants will die.
In this guide, we’re going to talk about what cold damage in cacti looks like and what you can do to save your plants if they’ve been caught in a freeze.
Here are the topics I’ll cover:
What Temperatures Can Cacti Tolerate?
Cacti are succulent perennials in the Cactacaeae family and with over 1700 known species these plants are extremely diverse.
They come in a huge variety of shapes, sizes, and temperature tolerances.
Some species can’t even come near a frost, while others are quite happy when they’re tucked in under a blanket of snow.
Most are pretty adaptable to a range of temperatures as long as they don’t have to suffer with wet roots for any length of time.
I’ll tell you what, that beavertail cactus (Opuntia basilaris var. longiareolata) that I fell on while snowshoeing in the Great Basin of Utah didn’t care one bit that the conditions were below freezing.
I was suffering from more freeze damage than the plant was.
But your spiny pincushion (Mammillaria spinosissima) won’t brush off the cold so easily. An extended freeze will probably kill the poor thing.
So it helps to know which species you’re dealing with. It might be that your cold-hardy cactus doesn’t need any help at all if it’s exposed to cold. Or, cold might spell disaster.
The cacti that we typically grow as houseplants are desert species that are generally not able to survive in cold temperatures.
The fairy castle cactus (Acanthocereus tetragonus) can only experience brief periods in the 30s. Spiral cactus (Cereus forbesii ‘Spiralis’) shouldn’t be exposed to anything below 50°F.
If you know or suspect that your cactus has been exposed to colder temperatures than it can tolerate, then it’s time to move on to the next section.
Identify Damage
First, bring your plant back into warmer temperatures and look it over to identify any damage.
The most obvious sign of frost damage is blackened or brown areas of tissue that may be mushy and soft if you press them.
These dead areas of tissue are as a result of the water in the cells freezing, expanding, and bursting the cell walls – which kills them.
Often, damage will typically look like light, white areas, at first. These white areas usually turn black or brown and mushy with time.
Some species will collapse or wilt. Others will start to leak fluid from the damaged areas. Sometimes they won’t become discolored, but some parts will turn mushy and soft.
Over time, damaged limbs or spines might fall off. It can also happen that the plant might seem to have survived its ordeal by cold, only to die from the damage it caused up to two years later.
Tall, skinny, or columnar types tend to be damaged first on the tips.
Branching types tend to experience damage on the outermost branches. Flowers are almost always damaged by a freeze.
Revive the Plant
Now that you’ve identified the damage, how do you fix it? You’ll need to be a bit patient and wait a few weeks for all of the damage to show.
The full extent of the damage often won’t be evident immediately.
Any areas that are mushy and dark brown or black have to be removed. Other discoloration, like purple, yellow, or orange spots can be left in place.
They’ll likely eventually heal on their own. If these areas turn black, they’ll need to go, too.
Soft, mushy tissue won’t recover and will need to be removed, and if a large portion of the specimen is like this, it will likely die. But if the plant is still firm, there’s a chance it will recover. Cacti are pretty good about healing themselves up given the chance.
Bring the plant into a warm, protected area if you can. Plants in the ground can obviously be left in place.
Make sure you don’t water the plants, ideally they should dry out a bit after the cold-temperature ordeal.
For plants growing outside, avoid pruning until spring when all risk of frost has passed. If you can keep the plant inside, you can prune it as soon as you’ve waited a few weeks for all the damage to appear.
When you’re ready, cut off all of the mushy bits. Go at least an inch but preferably more past the mushy area.
If there are any damaged and rotten spots left behind, they will continue to rot and this will spread to the rest of the plant.
So, while I know it hurts, you gotta do it.
Take a sterilized knife or pruners and trim off the damaged areas. You should do this until you only see healthy tissue remaining on the plant.
If you have to cut multiple areas, sanitize the tool again using a 10 percent bleach solution before making the cuts.
You might have to remove the entire top of a columnar species or several branches of a branching type.
Treat the cut areas with sulfur powder to help protect them from fungal invaders.
Bonide Sulfur Fungicide
You can find Bonide Sulfur Fungicide available at Arbico Organics in one- and four-pound containers.
Keep an eye on the cactus for the next few months. The cut area should develop a corky callus.
If it doesn’t, and instead it starts to rot, you didn’t cut far enough into the healthy tissue. You’ll need to trim it again and start over.
Prevention
Aside from making a note in your gardening journal or on your phone to remind you to bring your houseplants indoors before a cold snap, you can cover outdoor specimens with a frost blanket anytime the temperatures are forecast to drop below 35°F.
You can also cover the plants in pine boughs or move potted specimens into a garage.
Don’t remove the cover or put the plant back outside until the weather warms up again. It won’t hurt to leave the cover on for a week or more.
For species with long, narrow branching, you can protect just the tips of the branches to prevent damage.
My neighbor knitted adorable little caps that she puts on the ends of her cactus during a freeze, but you can use paper bags, cups, or something similar.
When you remove the cover, use caution, because any needles that are ripped off won’t regenerate.
You should also avoid watering your specimens in the days before a predicted freeze. Cacti survive a hard frost by dehydrating themselves so that their cells don’t burst when the water inside them freezes.
Rising From the Dead
Cacti are resilient. Don’t give up on yours just because it has suffered some damage. Chances are good it will recover so long as it hasn’t collapsed or turned completely white or black.
Sometimes all your plant needs is a little assistance from your end.
What kind of cactus are you growing? Is yours suffering from freeze damage? Or are you unsure? Let us know in the comments section below!
If you enjoyed this article and want to read more about growing cacti and other succulents, add these to your reading list next:
