A cactus needs less fertilizer than most plants, and it grows better with a little. Feed lightly, feed only while the plant is growing, and stop before fall where winters bring frost.
The short version
- Buy a fertilizer whose 3 label numbers are equal, such as 10-10-10, or whose first number is lower than the second, such as 5-10-5.
- Mix it at half the strength given on the label.
- Feed 1 or 2 times a year, in late spring or summer. A fast grower outdoors in strong light can take 2 or 3 feeds.
- The most to give is 1 feed a month from June through September.
- If the plant spends winter outdoors where it frosts, give the last feed in August. Give no fertilizer in fall or winter.
- Do not feed an unrooted cutting or a plant you have just potted or planted. Wait until you see new growth.
- If you are unsure whether to feed, skip it. A cactus gets by without fertilizer, and too much can damage its roots.
Do cacti need feeding?
In the wild these plants live on what the soil supplies, and most do the same in a garden. A light feed early in the growing season still gives more growth and a stronger plant. The growing season is the warm part of the year when the plant is putting on new stem, new spines or flowers.
In a pot. The roots can reach only what is in the pot, and watering washes nutrients out of a potting mix. Feed a potted cactus lightly while it is growing.
In the ground. Fertilizer is generally not necessary. If you want more growth from the plant, give it a light feed early in the growing season and leave it at that.
What to use
Every fertilizer label carries 3 numbers, such as 5-10-5. They give the percentage by weight of 3 nutrients, always in the same order: nitrogen, then phosphate (which supplies phosphorus), then potash (which supplies potassium). A bag marked 5-10-5 is 5% nitrogen, 10% phosphate and 5% potash.
Either of 2 kinds suits a cactus.
- A low-nitrogen fertilizer. The first number is lower than the second, as in 5-10-5.
- A balanced fertilizer. The 3 numbers are equal or close, as in 10-10-10.
Use either at half the label strength. Many growers find that heavy nitrogen pushes fast growth that is weak, and they choose a low-nitrogen fertilizer for that reason.
Liquid or slow-release. A liquid or water-soluble fertilizer is mixed into the watering can, so you decide when each feed happens. A slow-release fertilizer comes as pellets that feed for 3 to 4 months. Apply it once, in spring, and do not add liquid feeds on top of it.
Do not use fresh manure. It is high in salts, and salts damage roots.
How much and how often
Strength. Mix liquid fertilizer at half the rate given on the label. If the label says 1 teaspoon per gallon, use half a teaspoon.
How many feeds. Pick the line that fits your plant. If none clearly fits, use the first.
- Most cacti, indoors or outdoors: 1 or 2 feeds a year, in late spring or summer. An indoor cactus grows slowly, so it uses less.
- Fast growers outdoors in strong light: 2 or 3 feeds a year. Torch cactus hybrids, clumping Trichocereus grown for their large flowers, are fed on this schedule for strong growth and flowering. It is also a reasonable ceiling for fast columnar cacti, the tall upright kinds such as San Pedro (a Trichocereus).
- The most to give: 1 feed a month from June through September, using a low-nitrogen fertilizer.
The schedule by climate.
- The plant is indoors all year, or outdoors where it never frosts: feed between June and September. The last feed can be in September.
- The plant spends winter outdoors where it frosts: feed between June and August. The last feed is in August, which makes 3 feeds at most.
How to apply it. Use the diluted fertilizer in place of a normal watering. In a pot, pour it over the whole surface of the mix until some runs from the drainage hole. For a plant in the ground, pour it evenly over the soil around the plant, where the roots are.
When to stop
Fall. Fertilizer in fall pushes a cactus to grow, and a cactus growing in fall is more easily injured by a freeze. Extra watering in fall has the same effect. Where winters bring frost, let the plant slow down from September on.
Winter. In the short, cool days of winter a cactus grows little and uses little fertilizer. Give none until late spring, indoors or out.
Extreme heat. Many growers also skip feeding during the hottest weeks of summer if the plant has stopped growing.
Unrooted cuttings. An unrooted cutting gets no water until it has rooted, so it gets no fertilizer either. Rooting takes 4 to 8 weeks. See how to root a cactus cutting.
Newly potted or planted cacti. Do not feed a plant you have just repotted or planted out, even if it already has roots. Wait until you see new growth at the top of the stem, then give 1 feed at half strength.
Signs of too much
Fertilizers are salts. What the plant does not use stays in the pot and builds up, and in high concentrations these salts damage roots.
- A white crust on the surface of the mix or on the outside of the pot.
- Growth that slows during the growing season.
- Brown, dead root tips. You will see these when you next repot. There is no need to unpot a plant to look.
- New growth that is fast and weak on a plant in good light. It is often a sign of too much nitrogen.
To fix it, stop feeding and flush the pot. Pour clean water through the mix and let it run out of the drainage hole, using at least as much water as the pot holds. Repeat several times. In a small pot it is simpler to replace the mix with fresh mix.
Your climate sets the length of your growing season. Growing cactus for your conditions covers how to work that out.
Sources
Cacti and succulents. University of Minnesota Extension, reviewed 2026. https://extension.umn.edu/garden-and-home/yard-and-garden/gardening-in-minnesota/cacti-and-succulents
Cactus, Agave, Yucca and Ocotillo. 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. University of Arizona Cooperative Extension, revised 2011. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1399.pdf
Plant Care Information: Torch Cacti, Trichocereus hybrids. Arizona-Sonora Desert Museum. https://www.desertmuseum.org/visit/sheets/TrichoX.pdf
Indoor Cacti. Clemson University Cooperative Extension, Home & Garden Information Center, 2015. https://hgic.clemson.edu/factsheet/indoor-cacti/
Reading A Fertilizer Label. Clemson University Cooperative Extension, Home & Garden Information Center, 2022. https://hgic.clemson.edu/factsheet/reading-a-fertilizer-label/
Fertilizer Toxicity or High Soluble Salts in Indoor Plants. University of Maryland Extension, 2023. https://extension.umd.edu/resource/fertilizer-toxicity-or-high-soluble-salts-indoor-plants
Fertilizer for Indoor Plants. University of Maryland Extension, 2023. https://extension.umd.edu/resource/fertilizer-indoor-plants