A cactus is watered the same way everywhere: soak the soil, then wait until it is dry. How long the wait lasts depends on your weather, your season, and whether the plant is in a pot or in the ground.
All of this applies to a cactus that has roots and is growing. A cutting with no roots gets no water until it has rooted, which takes 4 to 8 weeks: see how to root a cactus cutting. For a plant that has just arrived or just been potted, see what to do after your cactus arrives.
The short version
- Water thoroughly, until water runs out of the drainage holes. Then let the pot drain and empty the saucer.
- Do not water again until the mix (the potting soil in the pot) is dry 2 to 3 inches down. Check with a wooden stick or a finger.
- The weather sets the wait. The mix dries quickly in warm growing weather and slowly in cool weather.
- In fall, once nights stay below about 60 F, stop regular watering.
- Where winter brings freezes, keep the plant dry until spring. In a mild, dry winter, water only after 2 to 4 weeks without rain.
- A pot dries faster than the ground, so a potted cactus needs water more often.
- If you are unsure whether to water, wait. Roots die in soil that stays wet.
How a cactus uses water
A cactus stores water in its stem. When the soil is wet, the roots take water up quickly, and the stem holds it for a long time. That store carries the plant through drought. When it runs low, the stem of a cactus such as San Pedro (a Trichocereus) shrinks and wrinkles.
A cactus does most of its growing in spring and summer, and it needs regular water through those months to grow well.
The roots also need air. In soil that stays wet they suffocate and die, and rot follows.
Soak, then dry
Soak. Pour water over the whole surface of the mix until it runs freely from the drainage holes. A thorough watering wets the full depth of the pot, so every root gets water. It also washes out salts, the minerals that tap water and fertilizer leave behind in the mix. Every watering is a full soak, in every season. When a cactus needs less water, you soak it less often.
Let the pot drain. If it sits in a saucer, empty the saucer. A pot left standing in water takes that water back up, and the bottom of the mix stays wet.
Dry. Wait until the mix has dried before you water again. If you find any moisture when you check, wait.
How to tell the mix is dry
The surface dries first, while the mix below it can still be damp. Check below the surface.
- A wooden stick. Push a wooden skewer or chopstick at least 2 to 3 inches into the mix, deeper in a tall pot, then pull it out. If it comes out darker or damp, wait. If it comes out clean and dry, water.
- A finger. Push a finger 2 to 3 inches into the mix, or as deep as a small pot allows. If it feels damp, wait. If it feels dry, water.
- Weight. Lift the pot when the mix is dry and learn how heavy it is. A pot that feels heavier than that still holds water.
Water by the weather
A cactus uses the most water in warm weather, when it is growing, and little when it is cold and dormant (resting, not growing). The mix dries on the same pattern, so the wait between soaks changes with the weather.
- Warm weather in spring and summer: water as soon as the mix is dry.
- A cool or cloudy spell: the mix dries slowly. Keep checking, and expect a longer wait.
- Cold, with the mix still wet: do not water. Wet soil is most likely to cause rot in cool weather, when the plant is not growing.
In the desert, a cactus in fast-draining soil needs water about every 10 to 14 days in summer. A small pot dries faster than that. In cool weather a cactus can go for weeks. These are examples, and the dryness check is what tells you when to water.
Through the seasons
Spring. Begin watering when the weather warms and the plant is growing again.
Summer. Most cacti grow in spring and summer, and this is when they use the most water.
Fall. As the nights cool, the mix takes longer to dry and you water less often. Once nights stay below about 60 F, stop regular watering, so the plant goes into winter dry. A cactus that is full of water when a freeze comes is more likely to be damaged.
Winter. From here until spring, water only as your kind of winter calls for.
- Winters with freezes, outdoors or in an unheated space: give no water until the weather warms in spring.
- Mild, dry winters with little or no frost: water only if 2 to 4 weeks pass without rain. Give one full soak, then wait again. The aim is to keep the plant from shriveling.
- Rainy winters: give no water.
- Indoors in a heated room: give the plant a winter rest. Keep it away from radiators, and water no more than once a month, only if it starts to shrivel.
Pots and the ground
In a pot. A small pot dries faster than a large one. An unglazed clay pot loses moisture through its walls and dries faster than plastic or glazed ceramic. Pot size and material change how long the wait is. The method stays the same.
In the ground. A cactus that has settled into the ground needs water less often than one in a pot. In the desert, younger plants may need water no more than about every 2 weeks in summer and older ones perhaps only once a month. In a cool season with normal rain they need none.
When you water a plant in the ground, wet the soil around it and let the water sink in. Do not leave water pooled against the base of the stem.
Water quality and salts
Tap water carries dissolved minerals, and fertilizer adds more. As the mix dries, those salts stay behind and build up. The sign is a white or tan crust on the surface of the mix or on the outside of a clay pot.
Each soak that runs out of the bottom carries some salts with it. About a fifth of the water you pour in should come out of the drainage holes. If you pour in 5 cups, about 1 cup should drain out. When you see a crust, give one extra-heavy watering to flush the mix.
Rainwater is the better choice if you can collect it.
If you are unsure, wait
If you are in doubt, do not water. Too much water is one of the most common causes of loss, especially in cool weather.
If a cactus is wrinkled or shrunken, feel the mix before you do anything else.
- The mix is dry: the plant is thirsty. Give it a full soak.
- The mix is wet: the roots have died from staying wet and can no longer take water up. Do not water. Take the plant out of the wet mix, and email support@thoughtfulpricks.com for help with what to do next.
Also email us if the stem is soft, dark or wet to the touch. That is not thirst. It is more likely rot, which needs attention.
To match your watering to where you live, see growing cactus for your conditions.
Sources
Cactus, Agave, Yucca and Ocotillo. Jack Kelly and Rob Grumbles, University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1225.pdf
Problems and Pests of Agave, Aloe, Cactus and Yucca. Jack Kelly and Mary W. Olsen, University of Arizona Cooperative Extension, revised 2011. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1399.pdf
How to Transplant a Cactus. Michael Chamberland and Jack Kelly, University of Arizona Cooperative Extension, 2020. https://extension.arizona.edu/publication/how-transplant-cactus
Container Gardening in the Southwest Desert. Kelly Young, University of Arizona Cooperative Extension, 2016. https://extension.arizona.edu/publication/container-gardening-southwest-desert
Interior Plants: Selection and Care. Elizabeth Davison, University of Arizona Cooperative Extension, 1998. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1025.pdf
Cactus Care Tips from Garden Horticulture Staff. Desert Botanical Garden, 2023. https://dbg.org/cactus-care-tips-from-garden-horticulture-staff/
How to grow houseplant cacti and succulents. Royal Horticultural Society. https://www.rhs.org.uk/plants/types/cacti-succulents/houseplants/growing-guide
Cacti and Succulents. Missouri Botanical Garden. https://www.missouribotanicalgarden.org/Portals/0/Gardening/Gardening%20Help/Factsheets/Cactus%20and%20Succulents10.pdf
Common Problems and Issues of Succulents. Aaron Steil, Iowa State University Extension and Outreach, 2023. https://yardandgarden.extension.iastate.edu/how-to/common-problems-and-issues-succulents
Winter-hardy Cacti. PlantTalk Colorado 1028, Colorado State University Extension. https://planttalk.colostate.edu/topics/annuals-perennials/1028-winter-hardy-cacti/
Whitish Crust on Potting Mixes. PlantTalk Colorado 1338, Colorado State University Extension. https://planttalk.colostate.edu/topics/houseplants/1338-whitish-crust-potting-mixes/
Soil and Container Media Electrical Conductivity Interpretations. E. A. Hanlon, B. L. McNeal and G. Kidder, University of Florida IFAS Extension, 1993. https://ask.ifas.ufl.edu/publication/SS117
Hydraulic Strategy of Cactus Root-Stem Junction for Effective Water Transport. Hyejeong Kim, Kiwoong Kim and Sang Joon Lee, Frontiers in Plant Science, 2018. https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00799/full