While all succulents and cacti have different temperature tolerances, this guide will serve as a starting point from which to establish your own environment-specific temperature exposure practices.
The Effects of Temperature on Succulents and Cacti
As is the case with sunlight exposure, succulents and cacti prefer to live in the "sweet spot" when it come to temperature. Both ends of the spectrum, hot and cold, can cause irreversible damage to these resilient plants, so it's just a matter of paying attention to their condition and modifying the environment as needed.
In general, succulents and cacti do best in temperatures ranging from 40-80°F. While minor sways in temperature outside of this range are tolerable, sways of 5° or more can cause irreversible damage. Even more interesting is that when temperatures hover near the ends of the tolerable spectrum (around 40°F or 80°F) these semi-extreme temperatures can act "stressor", influencing the plant positively and causing more vibrant colors to be expressed.
In winter, it's best to keep succulents and cacti above freezing to avoid frost damage. Some varieties are actually frost tolerant and prefer cooler nighttime temperatures of 30-40°F, while more tropical varieties such as euphorbia and lithops prefer minimum temperatures of 50-60°F. For the moment, the easiest way to determine what temperatures suit your plants best is to do a quick Google search, e.g. "Ideal temperature for insert plant name here." Our own documentation will be available soon on each plant product page.
Extreme Cold and Extreme Hot
When succulents and cacti are exposed to freezing or subfreezing temperatures, they can, you guess it—freeze! When the water inside the plant's cells freeze, it expands, causing those cells to rupture and die. When the plant finally thaws out, the areas that suffered damage will begin to rot or scar irreversibly—a symptom that may take days to become noticeable. The best thing to do in this situation is to cut out the affected area with clean razor blade in order to prevent the spread of rot.
To prevent damage from frost and freezing temperatures temporarily, it's best to move your collection under a patio cover or inside of your home while the freezing temperatures persist. You can also cover your plants with a "frost blanket", which is essentially a thin piece of fabric used to insulate plants from cold. In areas of the country where freezing temperatures persist for months at a time (basically anywhere outside of California), plants should be brought indoors for the winter, or into a sunroom or greenhouse with with bright natural light.
Cold temperatures aren't the only villains in this story though; hot temperatures can do just as much damage if left unchecked. When temperatures get to be too hot (90°F and up), a whole host of things can happen to your plants, especially when paired with full-sun exposure—leaves can shrivel and/or burn, water in the plant cells can steam and burst, and root systems can get fried.
Succulents that are planted in the ground with established root systems are able to tolerate extreme heat and cold much easier than those planted in containers because soil is not a great conductor of heat or cold. Containers on the other hand conduct heat and cold quite easily, focusing those extremes directly on the plants root system.
As with everything else in life, there are always exceptions to the rule. Some succulents can handle temperatures well below freezing and some can handle temperatures into the 100s. The easiest way to tell what varieties do well in your particular climate is to drive around and see what types of succulents your neighbors are growing successfully.
Moisture and Extreme Temperatures = Bad News
One of the most problematic combinations of environmental conditions is extreme temperatures and moisture. You should always avoid any scenario in which your plants are simultaneously hot and wet or cold and wet. Plants in dry soil, whether in the ground or in containers, fare much better than those that are not. In extremely hot conditions, water in the soil can begin to steam and "cook" your plants. In freezing or subfreezing conditions, water can obviously freeze, damaging the root system and causing rot. If you absolutely need to water your plants when extreme temperatures are forecast, do so early in the morning before 7am if possible.
The TLDR (too long, didn't read) SummarySucculents like average temperatures much more than the extremes. Cold temperatures can cause frost damage, while hot temperatures can cause burning and atrophy. The easiest way to make sure your plants are happy is to pay attention to what they are saying. If they're getting frost damage, bring them inside or cover them with a frost blanket. If they are burning or atrophying, move them to a shaded area or cover with shade cloth.
The Next Steps
Now that you've become acquainted with how temperature affects succulents, it's time to learn about the not-so-pleasant world of pests and disease.