A cactus with roots needs a pot that lets its potting mix (the soil in the pot) drain freely and dry out between waterings. A cutting without roots is rooted first, as described in how to root a cactus cutting.
The short version
- Choose a pot only slightly larger than the last one, about 1 inch wider. In a pot that is too large the mix stays moist and the roots can rot.
- Avoid shallow, wide pots. A tall plant needs a heavy pot wide enough to stay upright.
- Clay dries faster and weighs more. Plastic and glazed ceramic hold moisture longer.
- The pot must have drainage holes. A gravel layer in the bottom is not needed.
- Repot in spring, as new growth begins, using dry mix.
- Put the plant back with the same side facing the sun.
- Wait about a week before you water, and longer in cool weather.
Pot size
In a pot that is too large for the roots, the mix stays moist and the roots can rot. Move a cactus into a pot only slightly larger than the one it is in. About 1 inch wider across the top is enough. For a plant in a 4 inch pot, that means a 5 inch pot.
A cactus grows well slightly pot bound, which means its roots fill the pot. Roots filling the pot are not, alone, a reason to repot. The signs that a plant needs a new pot are listed under "When to repot" below.
Pot shape, and keeping a tall plant upright
After watering, a layer of wet mix sits at the bottom of every pot. A short, wide pot tends to have a wet layer at the bottom and less of the desired airy mix above it than a taller pot filled with the same mix. For any cactus, choose a pot that is deeper rather than shallow and wide.
Columnar cacti are the tall, upright kinds, such as San Pedro (a Trichocereus). A tall plant needs a heavy pot wide enough to stay upright. Clay weighs more than plastic, and a wider base is harder to tip. Test it with a gentle push on the pot. If the plant rocks or the pot starts to tip, move to a heavier pot or the next width up. Go no wider than it takes for the plant to stand steady, because the extra mix can stay moist for too long.
A stake can be used to hold a tall plant in place until its roots anchor it.
Clay or plastic
Unglazed clay, which includes terracotta, is porous. Water evaporates through the wall of the pot, so the mix dries faster and the plant needs watering more often.
Plastic is light and cheap, and it holds moisture longer. Glazed ceramic also loses no water through its walls, so it dries like plastic, and it is heavy like clay.
Choose by how fast pots dry where you grow.
- The mix is slow to dry. This is common indoors and in cool, humid or rainy climates. Clay's faster drying helps.
- Pots dry out fast. This is common outdoors in hot, dry summers, and with small pots, which dry faster than large ones. Plastic or glazed ceramic holds water longer.
- A tall plant where pots dry out fast. Glazed ceramic gives weight and holds moisture.
Growing cactus for your conditions covers how to judge your climate and your spot.
Drainage holes and gravel layers
Roots need air. In a pot that cannot drain, water fills the spaces in the mix and the roots suffocate. Every cactus pot needs at least 1 drainage hole, and several small holes are better than a single large one.
Empty the saucer after each watering so the pot does not stand in water.
A gravel layer in the bottom of the pot is not needed. It takes up space the roots could use, and a coarse mix all the way through drains well without it.
When to repot
Many growers repot young, fast-growing cacti every couple of years, and older plants when they see one of these signs:
- Roots are growing out of the drainage holes.
- The stem or its offsets (the side shoots at the base) fill the top of the pot, with little mix visible.
- A plastic pot is bulging or splitting.
- The plant has become top-heavy for its pot.
- The plant has stopped growing during spring and summer, when it should be growing.
- The surface of the mix has turned hard.
Spring is the best time, as new growth begins. Early summer also works. In midsummer a repotted plant is at greater risk of sunburn and heat stress, and in winter new roots are slow to grow in cool mix.
How to repot a spiny column
You need the new pot, dry cactus mix, good cactus gloves, and something to hold the plant. For a small plant, metal kitchen or barbecue tongs work. For a larger one, wrap the stem in several layers of newspaper or cardboard, and hold the wrap.
- Use dry mix. If the bagged mix is damp, spread it out to dry first.
- Mark the sunny side. Tie a loop of string around the plant with the knot on the side that faces the midday sun. That is the south side for a plant outdoors, or the side toward the glass for a plant at a window. If you do not know which side faced the sun, skip this step and shade the plant afterward, as described below.
- Take the pot off. It often helps to lay a tall plant on its side to do this, and to cut a plastic pot away if the roots are packed tight. Rest the stem on something soft, such as a folded towel or a piece of carpet. Broken spines and scraped ribs do not grow back. Do not lift a cactus by its roots alone.
- Clear the old mix. Shake or tease away what is loose. If the old mix is clearly different from the new one, for example dark and spongy where the new mix is gritty, remove as much as you can with your fingers.
- Trim damaged roots. Cut off broken or frayed roots cleanly with a sharp, clean blade.
- Let cut roots dry. If you cut or broke roots, leave the plant out of the pot, dry and in the shade, for a few days before planting. Dry wounds are less open to infection.
- Plant at the original depth. The old soil line is the mark on the stem where the mix used to reach. Put enough dry mix in the new pot that this line sits level with the new surface, hold the plant upright, and fill around the roots. Tap the pot to settle the mix. Do not plant deeper for stability. Green stem buried in mix is prone to rot.
- Turn the knot back toward the midday sun, then remove the string.
Sun after repotting
A cactus turned so that a different side faces the sun is at risk of sunburn. Sunburned skin turns yellow, then straw colored where it dies.
Outdoors in direct sun, shade a repotted plant for several weeks. Use shade cloth rated to block no more than 30% of the light, or cheesecloth, and then take it away.
When to water again
Wait about a week after potting before you water, so that damaged roots have time to dry. Many growers wait 1 to 2 weeks, and longer when roots were cut. If nights are colder than 60 F, keep the plant dry until warm weather returns.
When you do water, water thoroughly, until water runs from the drainage holes. Then let the mix dry before you water again.
If something looks wrong
Dark, sunken areas on the stem that are soft and water soaked are rot. Stop watering and deal with it promptly. If you bought the plant from us and are unsure what you are seeing, email us with photos at support@thoughtfulpricks.com.
Sources
How to Transplant a Cactus. Michael Chamberland and Jack Kelly, University of Arizona Cooperative Extension, 2020. https://extension.arizona.edu/publication/how-transplant-cactus
Problems and Pests of Agave, Aloe, Cactus and Yucca. Jack Kelly and Mary W. Olsen, University of Arizona Cooperative Extension, 2011. https://www.extension.arizona.edu/sites/default/files/2024-08/az1399.pdf
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
Indoor Cacti. Clemson Cooperative Extension Home & Garden Information Center, 2015. https://hgic.clemson.edu/factsheet/indoor-cacti/
Cacti and Succulents. Missouri Botanical Garden. https://www.missouribotanicalgarden.org/Portals/0/Gardening/Gardening%20Help/Factsheets/Cactus%20and%20Succulents10.pdf