How to Repot a Cactus

Removing the Cactus from Its Old Pot

Know when to repot. For most cacti species, you will need to repot the plant once its roots begin to show through the drainage holes of your pot or once the crown of the cactus reaches the edge of the pot. This will usually occur every two to four years. Repot your cactus during the dry season, usually in late winter or early spring. Roots may break during the process, and moisture can cause those broken roots to rot. It may also be time to repot if your cactus is very top-heavy. You should also repot if the soil is hydrophobic, or unable to fully absorb water.

Put on gloves. Slip on thick leather gloves. The material must be thick so that it can help protect you against the prickly spines of the plant. Gloves alone may not be enough to protect your skin, but even if you take other protective measures, you should still include thick gloves among them.

Loosen the soil. Run a dull knife around the inside perimeter of the pot, using a sawing motion to help break up the soil there. Continue as needed until the soil starts coming up as a solid mass. If you have a plastic pot, you could also try squeezing the sides of the pot to loosen the soil there. Tap along the sides of the pot with a dull knife to help loosen the soil, as well. The soil surrounding the root mass should be completely loosened before you remove the cactus. Otherwise, you could end up damaging the plant.

Lift the cactus out with newspaper. Stack a few sheets of newspaper together and fold them in thirds to create a thick, sturdy strip. Wrap this strip around your cactus. Carefully grab this strip, pressing it against the cactus as you work, and lift both the strip and cactus up and out of the pot. Alternatively, you could skip the newspaper and use an old pair of barbecue tongs to lift the cactus out. The idea is simply to keep your skin as far away from the spines of the cactus as possible.

Preparing the Cactus for Its New Pot

Clean the roots. Place the cactus on your working surface and use your fingers to brush off large pieces of soil from the roots. Carefully separate the roots, as well. The roots do not need to be completely clean, but most of the loose pieces of debris should be brushed away. Keep your gloves on during this part of the process.

Inspect the roots. Check the roots for signs of rot, diseases, or pests. Treat these problems as needed when you come across them. Apply a fungicide to get rid of rot or other fungi. Apply a gentle pesticide to get rid of any pests. Use small clippers to cut off any roots that appear dehydrated or dead.

Consider pruning the roots. Root pruning is somewhat controversial, and your cactus will likely survive the repotting procedure even if you leave the roots alone. Pruning the roots may help the plant thrive more efficiently, though, especially if done right. Large tap roots take in very few nutrients. They transport and store nutrients but do not actually absorb many, so they do not help the cactus grow faster. Cutting the larger roots can promote the health of the capillary roots, which are responsible for drawing in water and nutrients. Use a sharp, clean blade to cut back the primary taproot by one-fifth to one-half its current size. Cut the larger roots as well, shortening them by one-fifth to one-half their size.

Allow the roots to dry out. Keep the cactus in a warm, dry area for about four days to let the roots dry out slightly. The roots may get damaged when you remove the plant from its pot, and any breaks are likely to become infected with fungi or rot. The roots will be similarly vulnerable if you decide to prune them. Letting the roots dry removes this risk of infection.

Placing the Cactus in Its New Pot

Use the next pot size up. When selecting a new pot for your cactus, you should only choose a pot that is one size larger than the pot you removed the plant from. Anything larger may cause problems. If a pot is too large, the soil will end up storing more water. This water can linger around the roots and eventually cause them to rot. Large pots should be avoided for varieties that commonly experience root rot, like Astrophytum, Ariocarpus, Lophophora, Aztekium, and Obregonia. This is not as important for hardy species, though, like Cereus, Trichocereus, Hylocereus, Stenocereus, Myrtillocactus, and Opuntia.

Put a little soil in the new pot. Place a little coarse potting soil in the bottom of the new pot. Use enough potting soil to keep the cactus planted at the depth it was originally planted at within in the old pot. You may also want to consider laying a layer of drainage material, like gravel or broken clay pots (crocks), at the base of the pot before adding a layer of soil.

Wrap newspaper around the cactus. If you do not have the newspaper you used when removing the cactus, prepare another strip by stacking a few layers on top of one another and folding them into thirds. Snugly wrap this newspaper around the body of the cactus. Make sure that you have a good grip on the cactus through the newspaper. You should have your thick leather gloves on during this part of the process, as well. If you do not have newspaper available to you, old, clean barbecue tongs can also work.

Hold the cactus in the middle of the pot. Carefully pick up the cactus using the newspaper and place it in the center of its new pot. Rest it on or just above the soil in the bottom of the pot. Never press the cactus into the soil. Doing so can cause severe damage to the roots. You'll need to carefully fill the roots in with soil in order to secure it without causing harm.

Add soil around it. Carefully fill in the space around your cactus with more coarse potting mix. Sprinkle in as much as needed to hold the cactus in the center of the pot without packing the soil in. Once the sides are roughly halfway full, gently tap the sides of the pot. This encourages the soil to get into the root mass gently. Repeat this step again once the sides are completely filled in. At this point, you should also make sure that the plant is not too deep or not too high. Carefully adjust the position of the cactus in the pot as needed so that the green portion is above the soil while the brown root portion remains below the soil.

Consider adding compost and gravel. While not strictly essential, a layer of compost can help maintain proper soil acidity and a layer of gravel or grit can improve drainage. The compost should be slightly acidic, with a pH between 4 and 5.5. Mix the compost into the soil along the sides of the pot. Only spread a thin layer of gravel on the soil surface, scattering it around the base of the cactus.

Give the cactus additional recovery time. For hardy species, wait several days to a week before watering your cactus so that it can continue drying and recovering. For species prone to root rot, wait two to three weeks before watering. After its recovery period ends, you should be able to care for the cactus as you always have.