Watering Cacti During a Heat Wave

echinocactus LA

Written ByJen Greene

Posted: August 29, 2020

Care for cacti when it’s hot as hell

Recently, we experienced a multi-week-long heat wave here in San Diego. Where we are in inland North County, we had a couple days of 100F, with lows only reaching the high 60s or low 70s for some days. When it’s this hot and the sun is this intense, how should your watering routine change?

This depends, as with anything else, on your plants and your local conditions. Please keep in mind for all of my plants and the information below, I’m in zone 9b, with lots of sun, low humidity, and rain in winter.

General Routine

Not all cacti have the same requirements or response to the heat! I have mine loosely grouped into sections, with the species that thrive in hot, dry conditions together and those that need more water or shade grouped separately.

My routine for the past few weeks was to water the thirsty plants every 2 or 3 days, which I’d figure out by shoving my finger into the dirt up to the 2nd knuckle. Any pots too small or full of cactus for the finger test are easy enough to lift up and check the bottom to see if the drainage hole is dry or not. I try to wait until my cacti are completely dry before watering again, only watering more often if it’s extremely hot and I know the cacti will use the water to grow. The cacti that tend to fall into that category for me are the astrophytums, gymnocalycium, and just about any of the tall columnar cacti.

There’s several species that thrive on a bit of hot weather abuse, though, and those I monitor and try not to water too much. Copiapoa are a distinct example. I have mine potted in very well draining soil, and they are usually pretty dry. While I’ll typically be sure to thoroughly soak the soil for my other cacti and succulents, for the copiapoa, ariocarpus, and any cacti I’m rooting, I only lightly water the top of their soil, and make a point to spray the body of the cactus if it’s not a wooly type.

Time of Day to Water

I make an effort to only water my cacti at night when it’s hot, as cacti open up their areoles to absorb any humidity from the cooling air. By watering at night, and also watering their plant bodies, I help them more completely hydrate. I start my watering routine around 6 pm in July, when the days are longest, and slowly move up as the days get shorter. Now, in August, it’s cooling off enough or getting dark around 5:30 instead.

Notably, I am extremely cautious about watering my few ariocarpus. I have two young specimens that I water more often than nearly anyone recommends, mostly because I have them in such sparse soil. I’ll revisit these over time, but I believe the reason my frequent watering routine is working is because even with the regular water, they’re dry again by midday the next day.

How to Water – and How Much

I almost always water from the top on my mature plants, reserving bottom watering for the seedlings or soil that isn’t readily absorbing water from the top spray.

Watering the potted plants, which includes my cacti and succulents, can take me up to an hour to do thoroughly using the hose. I take my time, and make sure I can see water easily being absorbed and then running out of the bottom of the pots before moving on. If the soil is compact, old, or not absorbing water well (you can tell because it’ll pool on the top and bubble a bit as it works its way down), I’ll move on to a different area and then come back after a few minutes.

This type of watering, where you ensure that it’s running all the way through the soil and the entire pot has absorbed the water, is what is meant by “water thoroughly when dry”. A little sprinkle when the soil is completely dry isn’t enough in the conditions we have out there. You also need to pay attention to whether or not the soil is actually absorbing moisture, or if the water is just running right through! Check the edges of your pot as well as right by your plant every so often after you think you’ve watered enough. Is the soil soggy? Is it dry just below the visible surface? Or is it evenly damp throughout?

If you still have dry soil even when you see it running out of the bottom of the pot, that is a plant that’s a prime candidate for bottom watering (or butt chugging). That means the soil quality is low, or that it’s become compacted, and it’s not evenly absorbing water. For houseplants, that’s not a good thing, but for cacti, they tend to like soil that’s a little on the crummy side.

To butt chug your cactus, just stick the pot in a container of water, and leave it for about 30 min or so. You should be able to finger test all over the pot and see that the soil is moist throughout by the time you’re done. If not, you can leave it for another 30 min or even an hour, but too long with soggy roots at the bottom of the pot can do a lot more harm to your cactus than being dry.

I don’t recommend butt chugging as a regular way to water your plants, including cacti, because you end up not flushing any buildup in the soil out of the bottom of the pot. You can end up with hard mineral deposits or wonky soil pH, so if you find your plants constantly having caked soil or poor water absorption, it’s probably time to repot them.

Adapting for Your Climate

While I’m in a very hot, dry climate that pretty closely resembles nature for many of the cacti I keep, your climate may not be so similar.

You’ll have to watch your cactus or cacti closely to see how your conditions affect them. High humidity can dramatically impact water consumption. If your climate is very humid, you may only need to water your cacti once a month, even at the height of summer, due to the water it’s able to absorb through its skin. Additionally, while I can’t get away with just a light sprinkle of water for the top layer of a pot, you may only need a few ounces for your cactus if it takes weeks to dry out a thoroughly watered pot.

Lighting and temperature also play a huge role in watering. Colder cacti consume less water, as do cacti in lower light conditions. If you have your cactus indoors, be sure it has exposure to plenty of bright light.

Thank you for reading! 

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