Keeping Trichocereus through the cold
Dry, they take far more cold than wet. What to do about it in a pot, in the ground, in a greenhouse or indoors, and how to bring a plant back out in spring.
30-second version first, the whole guide below6 min read
The short version
- Most of keeping one through winter is keeping it dry.
- A plant goes into winter better lean than fat.
- Dry, they reportedly take nights down to about 25°F (−4°C), if it is back above freezing soon after sunrise.
- Get the mix dry before a cold spell and keep it dry through it.
- Stop watering before the first cold nights arrive.
- Never cover it with plastic: it carries the cold straight to the skin wherever it touches.
- A long or severe freeze can kill sections of a columnar cactus outright.
Your setup
Pick yours to see what changes in this guide.
Where it grows
In the ground
In the ground: the plant stays, so the cover goes to it.
Never cover it with plastic: it carries the cold straight to the skin wherever it touches.
In a pot
In a pot outdoors: bring it in before a freeze, to a place that stays dry and bright.
Young plants, new plantings and plants in pots are less tolerant than established plants in the ground, and a pot's roots sit closer to the changing air temperature.
Where it lives
Outdoors
Many columnar cacti are most sensitive at the growing tip, so that is the part to protect.
Indoors
Indoors: the winter rest is a cool, bright room, with nights near 46 to 50°F (8 to 10°C) and almost no water.
The season
Winter
A cold plant that is dry is usually fine.
Dry, they reportedly take nights down to about 25°F (−4°C), if it is back above freezing soon after sunrise.
Verne's Juul's Giant, from the cultivar library
Cold: reportedly it takes several days below 32°F (0°C) provided the soil stays dry, and some growers cover the growing tips during hard freezes in unheated greenhouses.
Not winter
A plant that has spent the winter indoors, under glass or in shelter has been living in shade by outdoor standards, and extension services say to bring it out gradually.
Lines are from this guide, or from the cultivar library where one says so. For where they come from, see the end of the guide.
Introduction
Cold and wet together is what loses these plants, growers say. Most of keeping one through winter is keeping it dry.
How cold they take
Growth stops when daytime highs stay under about 60°F (16°C), and about 55°F (13°C) is the trigger for , growers say. A dormant plant needs very little, and what it needs most is to stay dry.
- Dry, they reportedly take nights down to about 25°F (−4°C), if it is back above freezing soon after sunrise.
- With the usual cycles of wet and dry, nights down to about 35°F (2°C) are reportedly fine, while days still reach about 60°F (16°C). Colder than that, keep the mix dry.
One extension service also notes:
- Many columnar cacti are most sensitive at the growing tip, so that is the part to protect.
- A short freeze that is not far below freezing may mark only the , and the plant can grow out of it over several years. A long or severe freeze can kill sections of a columnar cactus outright.
- Young plants, new plantings and plants in pots are less tolerant than established plants in the ground, and a pot's roots sit closer to the changing air temperature.
Interactive
Cold and wet, or cold and dry
This opens on a wet winter outdoors in a pot, kept dry. Set the water dial to damp or to a full saucer and watch the verdict change. The plant and the cold are the same; only the water moved.
Season
Try a real place
The opposite answers, and both are right. Where winters are cold and wet, from northern Europe to the Pacific Northwest, a pot outdoors is dormant: no water at all, or one very light drink if the ribs visibly shrink, kept out of the rain and brought in before a freeze.
Likely outcome
Dry and dormant, which is what it wants
Growth stops when daily highs stay below about 60°F (16°C), and a cold plant that is dry is usually fine — growers say most varieties take nights down to about 25°F (−4°C) on dry substrate, if it is back above freezing soon after sunrise. Give it nothing through the cold months, or one very light drink if the ribs visibly shrink.
- Comfortable in part shadePart shade suits them. The trade is shorter spines and a slimmer, greener column — the same clone looks different grown this way.
Dry and dormant, which is what it wants. Growth stops when daily highs stay below about 60°F (16°C), and a cold plant that is dry is usually fine — growers say most varieties take nights down to about 25°F (−4°C) on dry substrate, if it is back above freezing soon after sunrise. Give it nothing through the cold months, or one very light drink if the ribs visibly shrink.
Getting ready
A plant goes into winter better lean than fat. Cut watering back as nights cool, so it goes into the cold a little shrunken instead of swollen with water that can freeze.
- Stop watering before the first cold nights arrive. By the time nights are near 35°F (2°C), or days stay under about 60°F (16°C), growers say, the mix in a pot should already be dry.
- Through winter, a potted plant in shelter gets little or no water, just enough to keep it from shriveling.
- Do not mulch it for winter the way you would a perennial.
Where you grow decides what you do
Growers and extension services say the same plant needs a different thing from you in each setup:
- In a pot outdoors: bring it in before a freeze, to a place that stays dry and bright. A potted plant brought in dry and kept in bright light should come through unharmed.
- In the ground: the plant stays, so the cover goes to it. On a night that is only just freezing, a cotton sheet, burlap or breathable frost cloth laid over it and taken down to the soil holds the ground's heat; take it off again when the day warms. Never cover it with plastic: it carries the cold straight to the skin wherever it touches. If only the tip is at risk, a Styrofoam cup over the growing tip, taken off each warm morning, may be all it needs.
- In a greenhouse: growers say it only has to hold the dormant range, about 35 to 55°F (2 to 13°C), and stay dry. Growers say it needs no extra lighting once it is dormant. Keep the air moving and the humidity low.
- Indoors: the winter rest is a cool, bright room, with nights near 46 to 50°F (8 to 10°C) and almost no water. Dormant plants do best at about 45 to 55°F (7 to 13°C), and want only enough water to keep them from shriveling.
- Out in summer, in for winter: stop watering as fall comes and bring the pots in before the first freeze. In spring, treat it as you would a new plant going outside: a few weeks in bright shade first, then more sun a little at a time.
After a freeze
Freeze damage shows over a few weeks, one extension service says: the exposed part blackens, then dries out and goes crisp. The same extension service says it cannot be repaired, but unless the freeze was long or extreme the damage may only be cosmetic, and the plant grows out of it.
Back outside in spring
A plant that has spent the winter indoors, under glass or in shelter has been living in shade by outdoor standards, and extension services say to bring it out gradually. Put it out as you would a new plant, growers say: bright shade first, then more sun a little at a time. Growers say one week's swing from cloudy and 80°F (27°C) to sunny and 95°F (35°C) is enough to burn a plant, and the scar stays.
Common mistakes, try it, quick check and sources
Quick check
Question 1: What do growers say is the danger to a plant resting through winter?
Question 2: A freeze is coming tonight and your plant is in the ground. What goes over it?
Question 3: A plant has spent the winter in a greenhouse. What happens if it goes straight into full sun on the first warm day?
