You can make more cacti by sowing seed, by rooting a piece of an existing plant, or by grafting a piece of one plant onto the roots of another. The 3 methods do not give the same result. Seed gives a new plant, a cutting gives a copy of the plant it came from, and a graft joins 2 plants into 1.
The short version
- Seed makes new individuals. A seedling is genetically different from each of its parents.
- Cuttings and pups make copies. A cutting is a piece of stem that is cut off and rooted. A pup is a side shoot that is removed and rooted. With few exceptions, both are genetically identical to the plant they came from.
- A graft joins 2 plants so they grow as 1: the top of one cactus on the rooted base of another.
- A hybrid is a cross between 2 different kinds of plant. Seedlings raised from a hybrid's seed often do not match it. To get the same plant again, root a cutting or a pup.
- Some cacti cannot make seed with their own pollen, and 2 cuttings from one plant count as one plant. For seed from those, start with 2 plants that were each raised from seed.
- Choose by what you want: a cutting or pup for another plant the same as the one you have, seed for numbers and variety, a graft for a cactus that cannot live on its own roots.
Seed: new individuals
A flower makes seed after pollination, the transfer of pollen to the flower, usually from another flower. The seed carries material from 2 parents, which is why the seedling matches neither. Seedlings from one fruit are generally not all alike, and now and then one shows something unusual in color, spines or shape.
Seed is an easy, cheap way to raise a lot of plants. Cactus seed is spread over the surface of a pot and covered lightly with coarse sand. It needs warmth and bright light out of direct sun. With nights at about 65 to 70 F, it generally germinates, meaning the seed sprouts, in 2 to 3 weeks depending on the species.
Seed is also a slow route to a sizable plant. A seedling is ready to be moved for the first time when it is about 1/2 inch across, and ready for a pot of its own at about 1 inch. A cutting starts at the size it was cut.
Cuttings and pups: copies
Many cacti root from a piece of stem. Columnar cacti (the tall, upright kinds such as San Pedro), prickly pears, chollas (the branching, cylinder-stemmed relatives of prickly pears) and many others are grown this way.
Cuttings. A length of stem is cut from the parent and left in the air until the cut end forms a callus, a dry, sealed surface over the wound. It is then planted to root. Cuttings taken when nights are 60 F or warmer generally root well, so in cooler weather it is better to wait. Give an unrooted cutting no water until it has rooted. Rooting takes 4 to 8 weeks. For how to make the cut on your own plant, see taking cactus cuttings. For callusing, planting and how to tell when roots have formed, see how to root a cactus cutting.
A cutting can be the tip of a stem or a mid-section, a length of stem with a cut at both ends. A tip keeps the growing point at the top of the stem. A mid-section has none, and its new growth generally comes as side shoots from the areoles, the small pads that carry the spines. Choosing between the 2 is covered in cactus cutting or rooted plant. Which end of a mid-section goes down is covered in which way up a cactus cutting goes.
Pups. A pup, also called an offset, is a side shoot that a plant produces by itself, often at the base. Cacti that grow as a cluster of stems often make many. A pup may already have roots of its own while still attached. If it does, it can be potted as a small plant once it is removed. If it does not, it is handled like a small cutting: the wound is left to callus, then the pup is planted to root.
Grafts: 2 plants joined
In a graft, the lower plant keeps its roots and is called the rootstock. The piece set on top of it is the scion. The 2 are cut and held together until they unite, and from then on the rootstock's roots feed the scion. The 2 plants do not have to be close relatives, but more distant pairings fail more often.
The familiar example is the moon cactus: a small red, yellow, pink or orange ball on a green, 3-sided stem. The colored ball has no chlorophyll, the green pigment a plant needs to make its food, so it cannot live on its own roots. The green rootstock beneath keeps it alive.
In the Trichocereus collector community, grafting is used to take a small cutting from a rare plant and utilize the established hardiness of a more common mature plant like San Pedro 'PC' to accelerate its growth.
Clones and hybrids
A clone is one plant multiplied by cuttings, pups or grafts. However many pots it fills, it is still one individual.
A hybrid is the offspring of a cross between 2 different species or varieties. Seed saved from a hybrid often gives plants that differ from it. A hybrid you like is kept going by rooting cuttings or grafting pieces of it.
Getting seed from your own plants
Some cacti are self-incompatible: a flower cannot make seed with pollen from the same plant. The peanut cactus, a small clustering cactus, is one of them. Because pieces of one clone are the same individual, pollen from one piece does no more on another piece than it does on its own flowers.
You usually cannot tell by looking whether a cactus is self-incompatible. One sign is a plant that flowers and makes no fruit. If 2 plants were both grown as cuttings from the same parent, treat them as one plant. Seed becomes possible with 2 plants of the same kind that were each raised from seed, in flower together. Even then it is a chance, because 2 seed-raised plants can also be incompatible with each other.
Which method for which goal
- Another plant the same as the one you have: root a cutting or a pup. Start with taking cactus cuttings.
- A large plant soon: start from a cutting.
- Many plants, or the chance of something new: sow seed, and expect small plants for a long while.
- Seed from your own plants: grow at least 2 plants that are not copies of each other.
- A cactus with no chlorophyll: it lives only as a graft.
Sources
How to Propagate Agaves and Cacti from Cuttings and Seed. Jack Kelly, University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1483.pdf
Propagation (chapter 13). North Carolina Extension Gardener Handbook, NC State Extension. https://content.ces.ncsu.edu/extension-gardener-handbook/13-propagation
Gymnocalycium mihanovichii. North Carolina Extension Gardener Plant Toolbox, NC State Extension. https://plants.ces.ncsu.edu/plants/gymnocalycium-mihanovichii/
Neon color, prickly nature. Ralph Mitchell, UF/IFAS Extension Charlotte County, 2024. https://blogs.ifas.ufl.edu/charlotteco/2024/12/11/neon-color-prickly-nature/
Physiology and genetics of self-incompatibility in Echinopsis chamaecereus (Cactaceae). T. Boyle and A. Idnurm, Sexual Plant Reproduction 13:323-327, 2001. https://link.springer.com/article/10.1007/s004970100073