How to Propagate a Cactus: Offsets, Cuttings, and Seed

Pick the method the plant offers you

Which method you use is decided by the plant rather than by preference. A clustering cactus hands you rooted or half-rooted offsets every year; a solitary globular one gives you nothing until you either cut it deliberately or raise seedlings.

All of it happens in the growing season. Late spring and early summer are the window, because a cutting or an offset needs warmth and months of growing time to build a root system before the cold, dry rest arrives.

Offsets: the reliable route

An offset that has grown against the parent for a season usually has a few roots of its own already, and those plants establish almost without failure. Take them from a plant that has been kept dry for a week or two, so the tissue is firm and the wounds are small.

1. Twist or cut it free Hold the offset with folded newspaper and twist gently. If it does not release, slice it away flush with the parent using a blade wiped with alcohol. A clean flush cut heals better than a torn stub.
2. Dry the wound Stand it in a dry, shaded, airy place for three to seven days, until the cut face is dry and skinned over. A small offset needs three days, a fist-sized one a week.
3. Set it on the surface Rest it on barely moist gritty mix rather than burying it. Prop it upright with a few stones if it will not stand. Buried offsets rot at the base far more often than they root.
4. Water only once it holds Keep it dry until a gentle tug meets resistance, which means roots. Then start light watering and move on to the normal soak-and-dry cycle after another fortnight.

Removing offsets is also how you get a solitary-looking plant to flower. A parent feeding a ring of pups puts everything into them, and a cleaned-up plant often sets buds the following spring.

Stem cuttings and the callus

Cutting a stem is what you do to save the top of a rotting plant, to shorten a columnar one that has stretched, or to make several plants from one. The whole outcome depends on the callus, the dry skin that forms across the cut face.

A cutting put into compost before it has callused rots almost every time, and it rots from the cut face upward so there is nothing left to try again with. Larger cuttings need longer: a two-inch (5 cm) stem might need a week, and a stem four inches (10 cm) across can need three or four.

1. Cut with a clean, sharp blade Use a knife wiped with alcohol and cut straight across in one movement. Wipe the blade again between plants, because rot organisms travel on a dirty blade better than any other way.
2. Bevel the edge Pare the outer edge of the cut face back at a shallow angle so it dries slightly domed. This stops the rim drying faster than the center and pulling the core into a dish that holds water.
3. Stand it upright to dry Keep the cutting the right way up in an empty pot, somewhere warm, dry, shaded and airy. Never seal it in a bag. Wait until the face is hard and papery all over.
4. Pot it shallow Set the callused end just touching the surface of dry gritty mix and support it with stones or a cane tied loosely. Depth gives no advantage and buries the wound in damp.
5. Mist the surface, do not soak After a week, dampen just the top of the mix every few days to draw roots down. Only water properly once the cutting resists a pull, typically four to twelve weeks in.

The severed parent is not wasted. Left dry, the cut stump usually breaks and produces a ring of new heads from below the cut, and each of those can be removed as an offset in a later year.

Seed

Seed is the only way to raise a plant that never offsets, and it is far easier than its reputation suggests. What it asks for is patience: germination takes one to four weeks, but a seedling is still the size of a pea at a year old and takes three to eight years to reach flowering size depending on the type.

Unlike everything else with a cactus, seedlings want to stay damp and covered. That changes only after the first few months, when they are gradually hardened to the ordinary dry cycle.

1. Sow on a fine gritty surface Fill a small pot with sieved gritty mix, top it with fine grit, and stand it in water until the surface darkens. Scatter the seed on top and do not cover it. Most cactus seed needs light to germinate.
2. Cover and keep warm Put the pot in a clear bag or a propagator and hold it between 68 and 77F (20 to 25C) in bright indirect light. Direct sun through a sealed bag will cook the lot in an afternoon.
3. Wait, and do not disturb Seedlings appear in one to four weeks as green spheres, often still wearing the seed coat. Leave them sealed and untouched for the first two to three months, only opening to release condensation.
4. Harden them off slowly From about three months, open the cover a little more each week over a month until it comes off entirely. Then let the surface dry between waterings for the first time.
5. Transplant in the second year Move them into individual small pots when they are crowding each other, handling them with tweezers by the body rather than the roots. Keep them slightly damper than an adult plant for another year.

What usually goes wrong

Almost every propagation failure comes down to moisture arriving before the plant was ready for it, or to the operation being done at the wrong end of the year.

Keep a note of each batch

Label every cutting and seed pot with the date it was taken or sown and the parent it came from. Rooting times vary enormously between types, and after a couple of years your own dated records tell you whether a cutting that has done nothing for two months is still on schedule or has already failed.

Record the failures as well as the successes, with how long the piece was dried before potting. That one number is what you will want when you next take a cutting of the same size.