Something I’ve been asked about often, via email, Instagram, and in person, is about when to water a cactus. How can you tell when your cactus is thirsty and needs water? They don’t seem to do anything, so how do you know when it’s the right time?
If you’ve been accustomed to houseplants or succulents, the slow signals from cacti can seem like absolutely nothing is happening. This is particularly true if you’re growing your cacti indoors, whether with lights or on windowsills, and the ambient temperature stays moderate year-round. Should you water the cacti before they start showing signs? What signs should you look for? If you wait too long, will they die?
I’ll walk you through some photos of my more demonstrative cacti so you know what “very thirsty” looks like, as well as how to get them back up to plump and happy.
First, A Word on Seasons
Most of the cacti you’ll encounter in cultivation have evolved to survive conditions that are seasonal in nature – meaning rainfall only occurs during summer or winter. Which season depends on the region, so it’s worth a bit of research into your species to figure out what they may need.
But!
It’s worth noting that in cultivation, your cacti will never experience the same sorts of seasonal stresses they would in habitat. Indoors, your cactus will never experience the 90F+ temperatures that it probably would in habitat. It’s not going to experience nights below 50F that tell it that it’s winter, and to stop growing.
At the same time, if the cacti are near a window, they’ll still get light signals that tell it what time of year it is: the angle of the sun and duration of sunlight hours give it clues even if the temperatures don’t.
This means it’ll know what time of year it is, but won’t necesarily be stressed out about it. That doesn’t mean other things won’t be stressful, but the requirement to go dormant to survive extreme heat or cold won’t be there. Since they’re plants, not thinking beings, they’ll go dormant anyway – but it’s not as stressful.
Kind of like the difference between being stressed out about being on time to work, vs. presenting in front of a group of people at work. If your job doesn’t require any speaking in front of groups, you don’t have that stress in your life – but you’d still be worried, or stressed, about getting to work on time, right?
So if you have cacti indoors, keep in mind it’s unlikely they’ll get the same degree of stressed that my (outdoor/greenhouse) cacti do. BUT – if you’re able to, let them get a little thirsty! This is to help you see some pretty visibly thirsty cacti as examples, so you feel more comfortable letting yours go longer before watering again.
Why Let Your Cacti Get Thirsty?
So a thirsty cactus isn’t necessarily a bad thing! While we as humans don’t enjoy stress, for cacti, it’s a necessary part of their lives. Some stress in the form of being a little water-deprived is a good thing, especially when they’re not experiencing enough heat to make them need lots of water.
Restricting water can help keep your cacti growing in a way they should, which is to say in a nice, compact, even way. Too much of a good thing like water can make them grow too fast, resulting in weaker bodies, fewer roots, and susceptibility to disease and rot.
So let them get a little thirsty. Indoors, you probably shouldn’t let them get as thirsty as I let mine get outdoors, though. Indoor conditions could take months, which would harm your roots and result in them dying back.
A thirsty Echinocactus viridiflorus
That Echinocactus viridiflorus is a good example of being at the point of thirsty enough to need more water, especially being out in the greenhouse. It’s a little bit wrinkled, it’s dark, and it’s a little squishy if I try poking it with gloves on. It’s not so thirsty it won’t produce flowers, which are visible as little funny buds sticking out of the side.
If you’re wondering how I know it’s thirsty, and not just supposed to look like that, you can see other examples of the plant when googling the latin name. Llifle, as ever, is a great example. Additionally, I’ve had the cactus for a couple years now, and have seen it go through thirsty/not thirsty stages. See below:
At left, before repotting, you can see that it’s nice and plump as well as green. It’s still got some ridges, but but the skin near the base of the plant looks tight and firm.
At right is it after being repotted, and needing to stay dry for a bit to let the roots heal. It’s a tiny bit thirsty in that photo, which you can tell by how it’s sort of…slouching, comapred to the one at left. If you can’t tell, you’re not alone! It’s pretty minor in photos, but I promise it’s more apparent in person.
The difference in time between the two is about 2 weeks during what was a pretty mild summer for us. The greenhouse was maxing out at 110F, with partial shade during the hottest part of the day. Many Echinocactus can very dramatically show the difference in how watered they are, and this species will shrivel down to next to nothing if kept continually dry. When I bought this cactus, it was little more than a nub in the pot!
So indoors, if you’re growing something similar, look for just that teeny bit of slouch or the slightly deflated looking appearance, and then give it some water.
Next up, a couple of my Gymnocalycium ragonesei. The cacti in focus aren’t the exact same plant, but you can see their neighbors in frame.
This particular species of Gymnocalycium has a pretty dramatic look of winter vs summer in my greenhouse conditions. You can see how flat and deflated it looks at left, which can be a pretty scary sight! It’s a much darker color, very purple-hued, which is an indication of stress. In this case, it’s very intentional stress that is healthy for them. The dry winter period keeps them from over-growing and stretching, keeping their growth tight and compact.
At right, you can see them plump and happy in summer! Hot summer temperatures and long days of sunshine are exactly what they love for growing. You can see that they are less stressed with the greener hue to them as well.
To get them to their winter state, I water less and less during the fall. When nights are getting in the 50s and 60s, I stop watering almost entirely. When they’re as deflated as the left photo, but nights are below 50, I’ll wait for a nice sunny day and then very lightly water them. That means just a little bit of a splash around the cactus, but I don’t sweat it if I get the cactus itself wet too. This keeps the roots from dessicating or getting so dry they die back, which is a risk in winter. You don’t want the cacti to have no roots left by the time spring rolls around, and they need to absorb water again to start growing!
I received this Coryphantha elephantidens cv. Titan in the beginning of fall, when it was still warm enough I was optimistic about getting it established before winter. You can see that it’s nice and green at left, when I first potted it up, but there’s some wrinkling of the outer parts of the cactus. When getting them rooted, it’s important to keep them a little dry to ensure any damage to the roots won’t rot your new cactus out!
You want to offer water on a very limited basis until it’s firmly rooted, which took longer than I expected for this guy. The roots aren’t as firm in the pot as I’d like, and it’s still a little loose when I wiggle it. As a result, it’s been watered very little, and it turned a bright red color as it got cold! My other specimen is still brilliant green, so the color change is a big indicator of how thirsty this cactus is. You can also see in the plant at right that it’s a bit more shriveled, so quite thirsty.
It can, and will, survive this just fine! I’ve started watering it now that it’s mid-March and we’re getting some warmer days, and I expect to see it really root and thrive. Coryphantha are very resilient and (usually) root easily, so longer days and warmer nights should help it along to really settle in.
What Cacti Look As They Recover From Very Low Water
When your cacti have been thirsty for a while, it can take them a while to really plump up! Outdoors, this tends to mean consistent watering over a period of time moreso than one really deep watering session. Watering thoroughly every week or two when they’re ready to grow lets them plump up slowly and fully recover.
At left, you can see a thirsty Opuntia “Santa Rita” with a Graptosedum “California Sunset”, a very pretty combo! The Graptosedum is showing signs of recovering from significant lack of water and hot summer temperatures. This combination of plants is next to our driveway and next to the retaining wall, so they are almost constantly hot and dry in summer no matter how much I water.
For those of you with Opuntia of your own, check the paddles of the one in the photo – you can see that it’s quite thin and wavy. It almost looks crinkled, and some paddles look thinner than others.
While thirsty, this is absolutely fine! Letting your Opuntia get this thirsty is how you can encourage them to have the beautiful purple color.
Again, unlike for humans, some stress can really bring out the beauty in our plants!
At right is a month later, after we had some nice rainfall that was able to soak into the soil. A nice gentle rain over several days, with a similar gentle rainfall a couple weeks later, gave these plants the moisture they were waiting for.
You can see how the paddles in the Opuntia are nice and plump, no waving to them or any sort of wrinkled appearance. The graptosedum in the planting with them are also getting paler and plumper from less stress and more water.
You can also see that the paddles lightened up in color! They’re still purple-hued, thanks to the full sun exposure, but the lighter color trending towards green is a sign of them being happy and ready to grow.
Even succulents (and cacti) that are in the same pot can have differing root systems and access to water, as evidenced by a neighboring set of Graptosedum.
The ones at the back, for whatever reason, haven’t been reocvering as well after all of our rain. This generally points to the root system dying back and being unable to absorb the water available to them in the ground. These serve as a good example of why you want to ensure your own plants don’t have their root systems dry out so much that they die!
The cure? In this case, I’ll likely trim back the ones that aren’t doing as well and replant the cut heads. Succulents will often root readily this way, with the plump stems having enough energy to produce new roots to seek moisture. Your cacti, if left super thirsty all winter and deflating like mine above, won’t necessarily have that same backup reserve to produce new roots. If it does, it’ll take that much longer to send roots out – and it’ll be at risk of rot if you give it too much water, and it sits in the wet soil.
All of that to say: Let your cacti dry out after you water them, but they shouldn’t stay completely dry for months on end, even indoors.
Above is my last comparison for you to show thirsty vs not thirsty, but in a specimen that hasn’t changed color. If you only looked from above, this Gymnocalycium pflanzii wouldn’t look too thirsty – the top is nice and plump looking, but then when you look at the side – those wrinkles!
I keep my Gymnocalycium pretty dry in winter, so they will get quite wrinkled like this – but usually only what you can see on the side. This is fine, this is expected, but as with many of my dry greenhouse cacti in winter, it’ll take a little while to get it fully plumped back up again.
Should your indoor cacti do this? Probably not. But if you do see it happening, it’s fine.
Now, let’s talk about how you get them back to plumpness!
Why You Should Take It Slow
If you start watering your cacti too heavily, too often, you can run into issues. Too much water too soon will cause them to split when they plump up, which is unsightly. When they heal up nicely, they scar, but the split opens up the cacti to pests and the risk of rot.
At right is one of my Astrophytum capricorne, showing a split near the base from getting plenty of water as I was waking these up for spring. That split is from last year, so it’s long since healed up, but the scar is never going away. The cactus is fine, and will continue to be fine, it’s just a bit unsightly.
In my Copiapoa hypogea at left, you can see that it’s also split in multiple spots. These are much more prone to such splitting, because they shrink much more dramatically than a firmer bodied Astrophytum.
Getting a Copiapoa like this to maintain perfect skin and not crack is difficult! Indoors, you’d have an easier time, as they wouldn’t need to be kept as dry over the winter months.
To keep them from cracking, when the weather warms up, you need to give them a little bit of water consistently as the temperatures get higher.
My method for waking them up in spring to try and minimize the risk of scarring is to start with just a little bit of water at a time – a splash, really. The splash gives them an initial bit of water to start waking up and regaining size.
After that, you keep doing small amounts of water, but consistently. Every couple weeks, splish splash, then let them dry out again. You should see them just starting to plump up. A good sign that they’re really waking up is that the spring bloomers start producing flower buds.
After a few rounds of this slow watering, when there’s a few nice sunny days forecast I’ll do a deeper watering. That first deep water, where I really let the water flow through so it is pouring out of the bottom of the pot, is the biggest risk for splitting. If I haven’t given them enough smaller drinks of water, the big deluge will give them enough moisture to plump up too much and the split will happen.
At least one cactus splits for me every year, especially the ones out in the ground (where I can’t control water thanks to rainfall), so don’t feel bad if that happens for yours, too. It does give me greater appreciation for the folks with old, established cacti in pots that they bring to their shows that have no scarring! The care it takes to make that happen is considerable.
I’m working on thirsty succulents next, with photos of my dudleys, blue chalk plants, and aeoniums! With us finally getting rain, I’ll have some great comparisons to share.
