Cacti and succulents can be a gardener’s best friend. They are easy, low maintenance, and can grow just about anywhere, indoors or out. Some might say they require no care at all. But those folks would be wrong. Just like any other plant, cacti and succulents do require care. It is just a different kind of care than many traditional plants you are accustomed to.
How do you water a cactus? Saturate the soil, then allow it to fully dry out before watering again. In landscape, for desert cacti, you want a dry depth of 2” or more, depending on cactus size. For indoor potted cacti, a dry depth of at least 1½” to 2” is best. Good drainage is key to avoiding root rot.
There is an old joke… how do you water a cactus? VERY carefully! Though that is true, there is a lot more involved than wearing chain mail gloves and standing 6’ away. Issues include where is the cactus located, what season is it, what kind of cactus or succulent do you have, what type of soil are you using, what is the ambient temperature and on and on and on? Each answer can play a role in “how to water cactus.”
Cactus or Succulent?
First, not everyone knows if they have a cactus or a succulent. These are different, but related plants. A cactus is a type of succulent, but not all succulents are cacti. With me so far? An example might help. A Prickly Pear or Saguaro is a cactus. Aloe Vera is not a cactus, but it is a succulent.
In this context, a succulent is defined by Cambridge Dictionary as “a plant such as a cactus in which the leaves and stem are thick and can store a lot of water.” On the other hand, a cactus is defined as “any of a type of plant that grows in the desert, having thick stems for storing water and usually spines”. There are more than 1,750 different cactus species throughout the world.
In a true cactus, the base or “stem” is extremely thick and almost tree-like in some species. The “spines” or “thorns” are actually modified leaves, that help reduce moisture loss by being tightly furled. Like more traditional plants, cacti have stomata to exchange oxygen and carbon dioxide with their environment. However, in cacti, the stomata are located in the base or trunk, rather than the leaves.
A cactus stores water in its trunk/stem. In some species, you can actually see the plant change in size and shape before and after thorough watering. The barrel cactus and the saguaro cactus are both good examples of that. Pad-type cacti, like the prickly pear for example, also store water in their pads.
There is an incorrect assumption that cacti (the plural of cactus) do not need water, or at least not much. Not accurate. Cacti are much better at storing water than other plants, but that does not reduce their need for water.
Cacti are simply very drought resistant. Their natural environment is the desert, where water comes and goes intermittently. When there is good access to water, the base will expand or the “pads” will expand, depending on species.
If you have ever cut into a cactus or a succulent, you know the interior is a wet, juicy, pulpy material. This is how the water is stored. As water is needed, the cactus can pull it from the pulp and use it in normal cellular functions.
Additionally, during dry time or drought conditions, most cacti can go into an almost suspended state. Growth is greatly reduced or stopped until conditions improve.
Succulents, overall, also need less frequent watering than cactus because they also are able to store water in their fleshy areas. Unlike cacti, succulents lack substantial spines or thorns as a prominent feature.
Location and Soil Type
Now that we’ve identified if you have a cactus or a succulent, the next thing to note is where is your plant located and what type of soil does it have?
If your cactus is indoors, planted in a pot, you are able to control external variables like heat, humidity and sunlight. The most important thing to note, in this event, is what type of soil is in your container? Cacti, and succulents in general, prefer soils that drain or percolate very well. The worst thing you can do to your spiny little friend is to put him in some peat moss and keep him damp all the time.
Cacti do best in loose, porous, pebbly or sandy soil materials. They require good aeration and, as noted, plenty of drainage. Their root systems are specialized to live within these harsh conditions.
- First, they are covered with a cork-like outer layer, that helps reduce water loss to the soil itself.
- Second, they have an extensive shallow root system that acts almost web-like to catch as much water as possible when it is available. New roots form quickly when water is available.
- Third, cacti are able to dehydrate new root growth when the soil begins to dry. This leaves small air pockets in the soil, preventing any water from seeping back out of the root system.
Living in a pot in your home, you need to keep this root system in mind. Make certain your pot is more than adequate to allow for good root growth. Remember, we’re talking lateral growth, not vertical. With controlled environments, most cacti will not need to be watered more than every 10 days, or so. The biggest risk you have with this situation is overwatering the little guy and causing “root rot”.
Cactus roots are simply not designed to sit in a wet environment. You need to water very thoroughly, then allow the soil to completely dry out before another watering occurs. Check soil depths as far down as 2” to make sure they are fully dried before you water again. Do not “mist” your cactus. It does no good, whatsoever.
I live in Arizona. We get less than 9” of rain annually. However, over 2/3 of that comes in a 2-month timeframe. We call them the “monsoons”. A storm will build over the course of the day. In the afternoon, a torrential rain may occur. It can drop up to ½ inch or more in less than 30 minutes. Then, it’s gone. These storms pop up in different locations and rain off and on throughout the entire southern third of the state in the months of July and August.
Beyond that….it’s dry as a bone. Seriously, the lead-in story on the news is when it rains. Cacti LOVE it! Most desert environments are comparable. It is VERY hot and dry 9-10 months per year. Then, you have a short “wet” season, where the rains will torrent down. Flash flooding is common. This is prime growth season for cacti.
Because deserts tend to have sandy soils, the water drenches the roots well, but does not linger. This wet/dry cycle is the key to good cactus water management. You need to mimic this watering cycle, as best possible. You need a good draining, loose type of soil. Do not go out and buy moisture-retaining mulches, this will just lead to root rot.
When the weather is hot, DRY, and sunny, you will water more frequently. If it is cooler, or you live in a humid area, your watering levels will decrease. Some species actually go dormant during the off-growing season. In that event, you may go months without needing to water, depending on the rainfall in your area.
If there is a lot of humidity, the ground will stay wet longer, reducing your watering frequency. Like an indoor plant, when you do water, you will want to saturate the soil, then allow it to fully dry out before watering again. With larger outdoor plants, you may need to check down as far as 6” to 8” to make certain that soil has dried.
What Type of Cactus Is It?
Regular, houseplant types of cacti generally come in two forms. The first is the “traditional” cactus. You know, spiny thorns, lives in the desert, grows in shapes likes paddles, balls and obelisks.
The other form is the “forest” cacti. This type of cactus is native to wetter, more temperate areas. Like their name indicates, they are indigenous to temperature forests, and include tropical and subtropical regions. A good example is the Christmas cactus. As you can probably guess just from that information, these cacti have very different care needs, including watering.
Traditional or Desert Cacti
As we discussed earlier, traditional or desert cacti prefer well drained soil. If you’re using a commercial brand, make sure it has a high perlite content. For forest cacti, regular potting mix is fine.
Traditional or desert cacti prefer temperatures in the 55° to 80°F plus areas. During their growth season, traditional cacti will do much better in the warmer temperatures, but you will want to keep them cooler and protect from drafts during their rest periods. They are also not fond of a lot of humidity. If you live in a humid area or it is during your rainy season, the desert/traditional cacti water frequency needs to drop substantially.
Forest or Jungle Cacti
Many forest cacti don’t really look much like cactus at all. They lack the spines or thorns we generally associate with cactus. They are usually either epiphytic, meaning they grow on trees or other organic materials or they are lithophytic, meaning they grow on rocks. Both get their water and nutrients from rain, dust, air, dead leaves, etc. Neither are parasitic, they simply utilize the other structures for support.
For obvious reasons, you will want your soil to mimic these conditions as closely as possible. Good soil materials include orchid bark, potting soil, pumice and oak leaf mold. It is important that the soil is loose, airy and provides extremely good drainage. Forest cacti are watered more like a regular houseplant than like a cactus. You will want to water it regularly during the summer months and especially when buds begin to appear.
During its resting period, you will water only when the soil is dry to the touch. Like other succulents and cacti, overwatering can result in root rot. Forest cacti have a temperature range comparable to desert cacti but will do well dropping to the 50s even during their growth season.
Unlike desert cacti, you will want to re-pot your forest cactus every 2-3 years. The best time to do so is after it has finished blooming. Providing fresh new soil mix at that time is a good idea.
With your forest or jungle cacti, you will want to water after the top 0.5cm (a little less than 1/4”) is dry. It the stem segments are shriveled, and the soil is dry, the plant is probably in need of water. Be careful, shriveled stem segments can also be a symptom of overwatering. The soil itself is the best gauge of watering frequency.
Other concerns that may affect your forest cacti include lighting and humidity levels. A really great resource for forest cacti specifically is worldofsucculents.com.
Identifying your type of cactus may be as easy as reading the little tag in the pot when you buy it. If not, you may need to do some research. There are some very good online sources for identification. My favorites include plantsam.com, cactiguide.com, and drought-smart-plants.com.
Watering Your Cacti
We’ve been addressing this question throughout our conversation, but I think it’s best if we pull it all together in one location. That way, we avoid any misunderstandings.
Watering Your Indoor Desert Cacti
Starting with indoor desert cacti. You will generally water these about every 10 days, or so. For the first month or two, there will be a little trial until you identify the best schedule for your cactus to thrive.
Thoroughly soak the soil. If your pot has a hole at the bottom, make sure the water is running through the hole. Begin checking soil moisture about 7 days later. If you have a moisture guide, that makes it easy. If not, put your finger in the soil. You want to be dry at least 2” down.
If you aren’t sure if it’s dry or not, a telltale sign is the soil being cooler toward the top than it is lower, that temperature gradient is indicative of moisture. When you hit that magic 2” mark, it is time to water again. Over the course of a couple of watering cycles, you’ll establish how often to water. Remember, watering frequency will need to increase when it is hotter than normal indoors. If you have evaporative cooling, it will need to decrease based on the increased humidity in your home.
Watering Your Indoor Forest Cacti
If you have indoor forest cacti, you want to fully saturate the soil. Again, if you have a pot with a hole at the bottom, make sure the water is running out the hole. If not, don’t be afraid to put some significant water on it.
Begin checking soil after 5 days. With forest cacti, you only need to be dry down about ¼”, rather than the 2” for desert cacti.
Some aficionados prefer to place a saucer of water under the pot and allow the cacti roots to pull the water up. This can work, but it is imperative the roots do not touch directly in the water, as that would lead to root rot. The safest way for your cactus is the soil down method.
There is no need to spritz or mist either type of cactus. They don’t get their moisture in this fashion, so it does absolutely no good, whatsoever.
Watering your Outdoor Forest Cacti
Honestly, most people keep forest cacti indoors, as they are a very decorative plant. However, that is not a requirement, so we should address the possibility here. Most do not do well in direct sun, so please be sure you have planted in an appropriate location.
You will probably want to maintain this in a pot, rather than plant it directly in the ground. If that is true for your forest cacti, begin with the same instructions as indoor plants. Do not be surprised if you have to increase water frequency to less than once per week, however.
During the warmer, summer months, the watering frequency may increase to as often as every 3 days, depending on temperature, wind and humidity levels.
Watering Your Outdoor Desert Cacti
Outdoor desert cacti are the trickiest of the bunch. So much is dependent on the temperature, humidity level, size of the plant and other variables. With smaller plants, less than 2’ high, the 2” depth margin for dry soil remains a good yardstick. However, if you have larger plants, like saguaro or good-sized prickly pear, you need to adjust accordingly.
Recommendations would be waiting to water until soil conditions are dry 3” down for plants 2’ to 4’ tall and dry down to 4” for plants taller than 4’. Regardless of height, you will want to saturate the soil thoroughly, remembering this must be good draining soil.
Overwatering = Root Rot
The biggest risk to your cacti, whether it is indoor or outdoor, desert or forest is the risk of overwatering. Remember how we talked about cactus roots being specialized to live in low-water environments? This specialization is what lead to problems with overwatering. When your cactus sits in too much water, the roots can’t handle it properly. The outer coating begins to break down and rot sets in.
Over time, you can actually see the rot occurring, as your base near the soil turns first mushy, then brown, then ultimately black and shriveled. All hope is not lost! The sooner you identify the rot, the more likely you are to salvage the situation and save the plant.
Here are the steps to salvaging an indoor plant with root rot:
1. Remove the entire cactus from the pot. You’ll probably want to use kitchen tongs or a comparable tool to do this. Place it gently on its side and remove as much dirt from the root system as you can without causing any further damage.
2. Trim off any roots that are brown, black, smelly, or oozing. The affected roots will be very obvious. It is recommended you use bypass pruners for this step. Dust the remaining roots with powdered sulfur and allow the plant to lay in the air, roots exposed for 1-7 days, to allow the cuts to scab over. Be sure to disinfect the pruners thoroughly before you put them away.
3. Using a pot (terra cotta is best) slightly larger than the former pot the cactus was in, fill it about 2/3 full of commercial cactus potting mix. Place the cactus carefully in the pot, without bending any of the now brittle roots. Fan the feet across the soil. Continue filling the pot loosely with enough soil to bring the level back to where it was in the former pot.
4. Wait about 2 weeks before watering the cactus deeply. Then, begin your water regimen again, remember to check soil moisture levels carefully before re-watering.
Steps to salvage an outdoor (landscape) cactus with root rot are a little different:
1. Mark the north side of the cactus with chalk before you begin to dig it up. It is important to keep the cactus oriented the same way when you re-plant. Uproot the cactus by cutting a circle around it with a shovel about 6” from the base. Be sure you use the shovel to lift it gently from the base area before lifting it from the ground.
2. Using tongs for smaller cacti or a garden hose for larger ones, move the cactus into a wheelbarrow and transport to a shady area to assess the situation.
3. Lay it on its side, with plastic sheeting underneath. Brush away as much loose dirt as possible to get a good view of those roots. Using pruning shears, remove any roots that are black, brown, soggy or smelly. Dust the remaining roots with powdered sulfur. Place a shade cover over the cactus and leave the roots exposed to air for at least 2 days to allow for scabbing over the cuts. Disinfect your pruners!!!
4. While you wait for the scabs to form, we need to identify the problem. It is probably a drainage issue, so let’s dig a hole about a foot deep where you’re going to re-plant. Fill the hole with water and wait for it to drain. Then, fill it again. This second-time monitor how long it takes to drain. If you’re draining less than 2” per hour, you have some work to do.
5. If we’ve identified a drainage issue in step 4, we’re going to address it here. Loosen the soil 18” to 24”. Add 2” of sand to the loosened soil and mix thoroughly. Test the drainage again by filling the hole and monitoring the drainage rate. If you have added more than 4” of sand with no improvement in drainage, you will need to prepare a large terra cotta pot full of commercial cactus mix to re-plant the pot in.
6. To re-plant, carefully place with cactus in the hole you’ve prepared or the partially filled terra cotta pot. Remember to face the chalk mark north. Carefully spread the roots out on the soil, while being careful not to bend them. Fill in soil around the cactus until you’ve reached the area the soil was at prior to the rot occurring.
Withhold water for 2 weeks. Then water deeply. Allow soil to dry out to a depth of 2” to 3” before watering again. Monitor your water frequency closely and check soil moisture routinely prior to watering.
Though cacti and succulents are wonderful plants to grow both indoor and outdoor, lack of knowledge about their needs and requirements can be deadly. I’m not suggesting you need to go become a cacti expert if Aunt Edna gives you a nice little Christmas cactus, but I am saying your lack to understanding its needs can be detrimental.
If you want that gift to thrive, or even survive, first you need to know what you have and how to care for it. Remember, Christmas cactus and other forest-type cacti prefer indirect sunlight, moderate temperatures and moisture frequencies of around a week. Let their soil dry out to a depth of at least ¼” before watering again.
Water requirements will fluctuate primarily based on growing season, interior temperature and humidity. Desert cacti love direct sunlight, warm temperatures and low humidity. Remember to let their soil dry out to a depth of at least 1½ “ to 2” if they are in pots and 2” or more if they are landscaped, depending on size.
Water requirements will fluctuate greatly throughout the year. Primary variables will include temperature, sunlight, wind, humidity and growing season. Take care of your cactus or succulent and you can enjoy it for years.