We have a cactus specialist on this forum which I really respect, lets hope X jumps in here. Norma

Not that I know much about the climate in Georgia, but I think it can be useful to know whether your plants are protected from rain or not. Moisture has a great impact on the survival rate in low temperatures. Sounds as if they are protected somehow.
How cold are your "cold nights"?

Chez Ron,

Welcome aboard. I've not the specialist's knowledge of X, and TJ is so much better at this than I am, but I can tell you a few things.

Almost all of those genera you mention slow down in the fall / winter. They don't mind being cold to some degree, but they don't want to be cold and wet. They, for the most part, can handle a light freeze, even, if they're dry.

For the most part, cacti don't need much water during the winter (their season of least activeness) - a sip or two a month during the coldest months is usually OK. As you say, you have some higher temps sometimes in the winter - it's probably a good day to give them that sip of water on that morning.

Some folk let them stay dry all winter, some give them some water (but not as much as the sluicings they get in the summer), it's really dependent on your type of soil, area where they are (lots of wind/reflected heat/light, etc), and so on; in other words, there are a few variables.

Personally, I don't move my plants in and out for the winter, but our temps are much colder than yours. It may work for some, but I'm lazy. I'd find a sunny spot inside and leave them there, the better to acclimate them.

If, OTOH, you have a covered patio, and you don't get many/any freezes, you might want to leave them as they are.

Your Lemairocereus's redness is probably due to cooler temps. C&S colours often change in response to temperatures and a lack of water/resources to grow (a stressed Aloe, depending on the species, will change from a well-fed green colour to one of deep, pleasing red).

Many of your Mexican cacti (the Turbs/ Feros/ Echinocereus) do see cold temps, and some freezing ones, but it's usually dry. OTOH, a number of your South American cacti (the Rebutias/Sulcorebutias/Parodias) don't usually see those temps, so you'll have to do some juggling. Generally (but not always) they're OK for short whiles at freezing if they're bone-dry. Too many C&S have I killed by being a little too free with the water, particularly in the winter, when sudden changes are more drastic, it seems. Plants will look dehydrated (and they are) - let them be. When in doubt about watering, don't. In the meantime, you can learn about your various genera and their growth likes/dislikes.

I don't really have much to add to this conversation. Things have been explained very nicely.

In your climate (southern US), the winters don't present much of a challenge. Just find a cool, dry spot for your cactuses and they will be fine when spring arrives.

However, the summertime can be a challenge. When you combine the heat, humidity, hot nights and frequent rain of a typical Georgian summer, it may be too much for most cactuses to handle if they are outdoors exposed to it all.

You need a strategy whereby your plants can tolerate these conditions. Let us know what you may have in mind and we can then give you some further advice.

x

Awesome answer MC Harris! Your answer is precisely why this forum is better than a book.

It is reassuring to know if I see them dehydrate this winter I shouldn't panic.

My books say minimum temperature for some of my cactus is 55 degrees F. Does that seem right to you? Thx.

I don't know about Lemairocereus, but the others on your list tolerate temperatures down to freezing and temporarily a few degrees lower. Cacti don't like to be alternately frozen and thawed, it stresses the plants, so most growers keep their plants above freezing. Some species are more sensitive and should preferably be kept at around 55-60F, but that it mostly Melocactus and other cacti from more tropical areas. For reasons I don't fully understand some books recommend minimum temperatures much higher than the actual values. But as I wrote earlier, it depends on humidity too. Cacti die more often from disease during long periods with high humidity, even at a "safe" temperature.

The reason books give high temperature recommendations is that the growers who provided the input did not expose their valuable or rare plants to cold conditions for fear that their plants are at risk.

I feel rather confident that prior to our current knowledge of root systems and soil physics, many growers were using peat in high amounts which weakened their collections. The result, not unlike what newbies experience here, was sudden rot when conditions weren't suitable. But they did not understand why the plants suffered and placed the blame on cold temperatures, excess watering, inadequate drainage, and other things that we know better today are not necessarily at fault.

x

If a hard freeze is predicted I bring in most of the cacti/succulents, just because, like you I'm in the south and the plants don't acclimate to cold. It's close to 90 right now. We go from 90 to 20 in a couple of hours. And I've found, growing in pots, they don't have the root protection of the ground. A light freeze, one lasting a couple of hours I leave most, if not all of them out, there are a few that are more sensitive to cold. The rain is more of a problem, those cold dreary rainy days that seem to last for a month.

Like X said summers are more of a problem. To solve the problem here, where humidity is rarely below 90% and monsoon type rains are common, I grow the majority of my collection in pots, with my own blend, on the roof of the porch. Full sun all day, wind (and salt spray) are pretty consistant which dries out the plants, plus it's a black asphalt roof. I have to water the cactus out there but they don't, as a rule, rot. There are some in the ground-the dirt here is little more than fast draining sand.
Tally HO!