How Often Do You Water a Cactus?
What Does a Cactus Need?
I don’t know about you, but I’m a very busy person. I have two small children–which on its own is a full-time job–but also have to cook, clean, run errands, and take care of the household. I’m not going to remember to water a plant every day, so it shouldn’t be any surprise that I would wind up with a cactus.
Originally, I thought that a cactus would be an easy plant. I quickly realized, however, that I had absolutely no idea how much (or how little) work it was going to take. I knew that I wouldn’t have to water the cactus every day, but I definitely had to ask, “What does a cactus need?”
Very early on as a cactus owner, I learned that there’s a pretty big difference between “thrive” and “survive.” Truth be told, I had always just assumed that cacti would thrive if they were left in a sunny spot and watered once every few weeks. Isn’t that what it’s like in the desert, after all? A cactus can survive under those conditions, but in order for it to thrive, it needs a bit more. Although cacti can survive without water for weeks on end, there’s no way that it’s going to thrive with that little attention.
Now, my cacti thrive. Here's what I learned.
How Often Do You Water a Cactus?
How much water you need depends on a wide range of factors, but the first thing to know is that not all cacti are the same.
"Cacti" is short for the specific plant family Cactaceae, but that umbrella term encompasses a wide variety of types that live in drastically different habitats and have vastly different needs. Many—like those in the genus Ferocactus—are the typical, hardy desert-dwellers that need little water, but the genus Echinopsis (from the grasslands of South America) and genus Oreocereus (from the high Andes mountains) both need a bit more water, while genus Epiphyllum (from jungles)—a cactus that roots in trees rather than dirt—likes cooler and damper habitats. Deciding how much to water depends on:
- The type of cactus that you have
- What its normal growing season is
- The typical temperature, soil, and conditions of its original habitat
- What type of temperature, soil, and conditions it's being grown in now
How do I know which type of cactus I have?
- Look at the container it came in. Usually, there will be a tag or a sticker to help you identify the type and understands its needs.
- Bring a photo to your local nursery for help with identification.
- Try to identify your cactus by looking at photos of cacti online, or see if your local library has a good reference book.
How Much Water Do Cacti Need, and How Often?
Water—either too much or not enough—is the hardest thing to get right and the most common reason cacti fail to thrive (or survive), but sweeping generalizations about how much and how often to water won't help you, since every type of cactus is different. Here are some general guidelines to follow:
- During the growing season (usually from spring to fall) cacti want regular watering and fertilizing. In the hottest, driest months, thoroughly water your cactus once a week.
- Always let your cactus dry out between waterings. The top few inches of soil should be completely dried out. A water gauge can help you determine the soil's moisture level, or you can stick your finger into the dirt to gauge the moisture level yourself.
- Of course, plants in pots need more water than those planted directly into the ground, so adjust accordingly.
- Many plants rest in a semi-dormant state from late fall to early spring and need less water then. If you live in an area that gets more water than that cactus's natural habitat, you won't need to water.
- Some say that cacti need a little water during their dormant season, but others say that they don't need any during winter. You'll need to test and watch carefully to see how much water your cactus wants.
- Watch for signs in the leaves or stems that show that the plant is getting stressed due to a lack of or excess moisture. An underwatered cactus might look deflated, rubbery, skinny, or pale. At first, an overwatered cactus might look happy and plump, with new pups growing, but waterlogging a cactus will cause its roots to die and rot, so eventually, the plant will get soft and pale. Catch the symptoms early and stop watering too much and often.
- Your water's hardness makes a difference. If your water is hard, re-potting is recommended every couple of years to prevent salt build-up.
- If potted, your cactus should be in a well-drained pot. Cacti never like to stand in puddles.
How to Water a Cactus
Alright, so how often do you water a cactus? Although it can depend on a number of the different factors which we’ve already talked about, there is a general rule of thumb that can be used for most varieties.
Most horticulture professionals agree that you should water a cactus around once a week in the hottest months. In most cases, this is the perfect amount to provide adequate moisture without causing too much water to remain in the soil and soak the roots.
When it’s time to water, do so until the soil is saturated. If you see water slowly dripping out of the drainage holes in the bottom of the pot, this is a sign that the soil is thoroughly soaked. If the cactus is in the ground, you can use your finger or a water gauge.
Signs Your Cactus Needs More or Less Water
Signs of Overwatering
Signs of Underwatering
cactus looks plump, full, and turgid
stems look desiccated, limp, rubbery, or soft
you can't see under the surface but if you could, you'd see that its roots are rotting
the plant may lean or slump to the side
pools of water under your cactus (cacti never like this)
entire plant may change color—usually they get paler
How Do I Know How Much Water My Cactus Needs Even If I Don't Know What Kind It Is?
If you don't know the proper name, place of origin, or care instructions for your cactus, answering these questions should help you determine how often to water.
- Does it have leaves or stems? Most species of cacti don't have true leaves, but some do. As a general rule, the thinner the leaf, the more water the cactus will need. Cacti with a high surface-area-to-volume ratio (like those with thin leaves) lose water at a higher rate than those with a low area-to-volume ratio (those with thick, fat stems).
- Does it have spines? If your cactus has lots of spines, it might need less water than one with few spines. Most cacti have spines, which are modified leaves. Although spines contain little or no water, they do help a cactus conserve water by trapping air on the surface, which creates an insulated layer that reduces evaporation and transpiration. Spines also provide a little shade, lower temperature, and reduce water loss. Spines are good at capturing moisture from the air.
- Does it have a solid stem? If so, it probably does a great job of conserving water itself. The stem is the main organ a cactus uses to store water. Both the round shape of a globular cactus and the cylindrical shape of a columnar cactus have low surface-area-to-volume ratio and do a great job of storing water. If the central stem is ribbed, this allows the cactus to shrink or swell with water like an accordion.
- Is it small or large? In general, small cacti need less water than large ones.
Is It a Cactus or Is It a Succulent?
"Succulent" is a larger umbrella term that describes any plant that stores water in its leaves or stems. Almost all cacti are succulents, but not all succulents are cacti.
In general, cacti are even better at water storage than succulents are. Cactaceae have fleshy stems that store water, spiny or hairy coverings, and few (if any) leaves.
Most succulents have leaves; most cacti don't. Notice I said "most," since the dividing line between succulents and cacti is blurry.
Cactus Nutrition: Do Cacti Need Fertilizer?
If you thought that the only thing you’d need to do to care for your cactus would be water it, I hate to be the one to disappoint you. But just like being watered, cacti need to be fed nutritional additives (natural fertilizers) on a regular basis.
Although they’re far more resilient than most other types of plants, cacti still need a good balance of fertilizers to help them thrive throughout their growing season. For most varieties of cacti, this is going to be in the warmer, more humid summer months.
However, there are many types that grow during the winter and lie dormant during the summer, so be sure to check the schedule for your specific species of cactus. While you still need to water cacti while they’re dormant, you don’t need to worry about the fertilizer. Most cacti prefer many small feedings rather than one gigantic dose of fertilizer.
What kind of fertilizer should I use?
Use a low-nitrogen type. Any type that is higher in phosphorus than nitrogen will do.
What Else Does a Cactus Need?
In addition to moisture and fertilizer, you'll also want to consider light, temperature, soil, and pot size.
How much sun does a cactus need?
Every type is different, but most cacti require a minimum of four hours of direct sunlight per day. If the plant is indoor, place it near a south- or east-facing window. They also like even exposure, so you'll want to periodically rotate the pot.
What temperatures do cacti need to survive?
They can take temperatures from 45°F to 85°F without complaint, as long as they are dry.
What kind of pot should you use?
If you're planting or re-planting in a pot, use one that's just large enough to fit the cactus. This will help ensure that the roots dry as quickly as possible. Consider widening or adding holes to the bottom of the pot to make drain-time even quicker.
What kind of soil should you use?
Drainage is more important than potting material, but the soil should be porous (not clay). Succulents without spines or needles tend to appreciate more humus (organic matter) in their potting soil.
Cactus Care Quizview quiz statistics
I was happy to discover that while a cactus’ water schedule might be a little more demanding than I had originally thought, it’s still a whole lot easier than worrying about most other types of plants.
I’m happy to report that my cactus is doing great, although I may still forget every once in a while!
If you’ve recently purchased a cactus, don’t be intimidated—if I can keep my cactus growing, I promise that you can, too.
Cactus Owners Poll
What type of cactus do you own?
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2011 SueWithTwo