Seed is the slow way to grow a cactus, and it gives you plants that are new rather than copies. Most cactus seed needs light on it, steady warmth, and clean, humid conditions that never turn soggy.
The short version
- Sow in a shallow pot with drainage holes, in new or oven-sterilized mix that is about half perlite or pumice and half peat or well-composted organic matter.
- Wet the mix from below, sprinkle the seed on top and dust it lightly with coarse sand. Most cactus seed needs light to sprout, so do not bury it.
- Cover the pot with clear plastic. Keep it in bright light out of direct sun, at about 68 to 80 F by day and about 65 to 70 F at night.
- Expect seedlings in 1 to 3 weeks. Some kinds take longer, up to a few months.
- Once they are up, lift the cover over a few days and then remove it. Keep the mix damp, never dry right through and never sitting wet, and raise the light a step at a time.
- If seedlings fall over, give them more warmth and air and keep the mix damp rather than wet.
- Transplant them in small clumps when each seedling is about 1/2 inch across, and into their own pots at about 1 inch.
- Each seedling is a different plant, and seedlings tend to grow slowly. For a copy of a plant you know, or a large plant sooner, start from a cutting.
What seed gives you
Every seedling is a new plant that differs from both its parents, and seed from a hybrid often gives plants that look unlike the parent. Seed cannot give you another plant identical to a named clone (one original plant, multiplied from cuttings and sold under its name). A cutting or a pup (a small offshoot of the plant) does that. See how cacti reproduce.
Seedlings tend to grow slowly. A cutting starts at the size it was cut, so it is ahead of any seedling from the first day. See cactus cutting or rooted plant.
What you need
- Fresh, clean seed.
- A shallow, wide pot or tray with drainage holes. If it has been used before, wash the pot with soap and water and let it air dry.
- Mix that drains well: about half perlite or pumice and half peat or bagged, well-composted organic matter. Leave out manure, which can hold seedlings back, and do not use garden soil or mix from an old pot. See cactus soil.
- Coarse sand, a waterproof tray deep enough to stand the pot in, and clear plastic wrap or a clear bag.
- A warm place in bright light out of direct sun.
- Labels and a pair of tweezers.
Sowing
- Use new mix, or sterilize it by baking it in an oven at 350 F for 30 minutes and let it cool. Clean mix cuts down damping off, a seedling disease.
- Fill the pot and stand it in the tray with water up to half the pot's height. Leave it until the surface of the mix is damp, then lift it out and let it drain. Water from below until the seed is up; cactus seed is small and easily washed out.
- Sprinkle the seed thinly across the top of the mix. Do not press it in.
- Dust it lightly with coarse sand. San Pedro seed is only about 1 mm long, so the sand is a thin dusting.
- Label the pot with the plant's name and the date, cover it with plastic, and put it in its warm, bright place.
Germination: light, warmth and moisture
Light. Seed of 12 relatives of San Pedro, including tall columnar kinds (upright, stem-shaped cacti), did not sprout at all in the dark, at any temperature. Seed that is buried, or a pot kept in a dark cupboard, may not come up.
Warmth. Cactus seed can germinate anywhere from about 63 to 93 F, best at about 68 to 80 F. Nights of 65 to 70 F suit germination and early growth. Indoors, a seedling heat mat under the tray can hold the mix at about 70 to 75 F.
Moisture. The plastic holds moisture in, and a little condensation on it does no harm. If the surface looks dry before seedlings appear, stand the pot in the tray again.
How long. In warmth, most cactus seed comes up within 1 to 3 weeks. If nothing has come up at 3 weeks, check that the pot is warm, lit and damp, and give it more time.
The first weeks
Once seedlings are up they need more air. There are 2 ways to handle the cover. If this is your first sowing, uncover over a few days.
- Uncover over a few days. Lift the sides of the plastic for a few days, then take it off. From then on, mist the surface, or stand the pot in the tray, whenever the top of the mix starts to look dry. Keep it damp but never sitting wet, and do not flood the seedlings, which can wash them out or spread disease.
- Keep it covered longer. Some growers leave the cover on until the seedlings have spines and are about 5 mm (just under 1/4 inch) across, then open it gradually.
Either way, growers treat a green film or moss on the mix as a sign the pot is too wet: give it more air.
Light. Start in bright light with no direct sun. As the seedlings grow, raise the light until they get early-morning sun, filtered light, or light through 50% shade cloth (a mesh that blocks half the sun). See acclimating a cactus to sun.
- Too much light: a seedling turning yellow on the side toward the light. Growers generally accept a hint of red, and take brown-red or bleached white as sun damage. Move the pot to more shade.
- Too little light: seedlings that grow lopsided, or columnar seedlings that stretch tall and thin. Give more light, a step at a time. See etiolation.
Once seedlings are about 1/2 inch across, you can feed them once a week with a fertilizer that dissolves in water, mixed at half the strength on its label. See fertilizing cactus.
Damping off
Damping off is a seedling disease caused by several fungi and a water mold. It thrives in cool, wet conditions, low light, overwatering and too much fertilizer. Seed may never come up, or seedling stems turn water-soaked and thread-thin where infected, and the seedlings fall over. In humid air, a fine white fuzz may grow on infected seedlings.
To prevent it, keep the mix and pot clean, keep the seedlings warm, water with warm water (about 68 to 77 F) rather than cold, and keep the mix damp but never soggy. If seedlings start to collapse, those same conditions are the fix: more warmth, more air, and mix that is damp rather than wet.
Moving seedlings on
Moving on means transplanting seedlings out of the sowing pot.
- Each seedling about 1/2 inch across: move them in small clumps into a tray or pots.
- Each seedling about 1 inch across: separate them and give each its own pot.
Some growers leave seedlings in the sowing pot until they are crowded, which can take a year or more. Whichever you choose, growers usually move seedlings once they start to touch, because crowded seedlings tend to rot.
Water lightly first, so the mix is soft and the seedlings come out with less damage. A common tool is tweezers or a plant label with a small V cut into its tip. Keep as much root as you can, and pot them in a cactus mix.
Seed from your own plants
Several close relatives of San Pedro cannot make seed with their own pollen, so a single plant often sets none. See cactus flowers and their pollinators, and for taking seed from ripe fruit, from flower to fruit.
Sources
How to Propagate Agaves and Cacti from Cuttings and Seed (AZ1483). Jack Kelly, University of Arizona Cooperative Extension, 2009. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1483.pdf
Are cactus growth forms related to germination responses to light? A test using Echinopsis species. Pablo Ortega-Baes, Mónica Aparicio-González, Guadalupe Galíndez, Patricia del Fueyo, Silvia Sühring and Mariana Rojas-Aréchiga, Acta Oecologica 36: 339-342, 2010. https://ri.agro.uba.ar/files/download/articulo/2010OrtegaBaes.pdf
Effects of alternating temperature on cactus seeds with a positive photoblastic response. L. T. Lindow López, G. Galíndez, M. A. Aparicio González, S. S. Sühring, M. Rojas-Aréchiga, H. W. Pritchard and P. Ortega-Baes, Journal of Arid Environments 148: 74-77, 2018. https://ri.conicet.gov.ar/handle/11336/93252
Cactus seed germination: a review. M. Rojas-Aréchiga and C. Vázquez-Yanes, Journal of Arid Environments 44: 85-104, 2000. https://doi.org/10.1006/jare.1999.0582
Identity and neotypification of Cereus macrogonus, the type species of the genus Trichocereus (Cactaceae). Sofía Albesiano and Roberto Kiesling, Haseltonia 17: 24-34, 2012. https://cactusconservation.org/wp-content/uploads/2020/03/Albesiano_Kiesling_2012_Haseltonia_17_24-34.pdf
Notes on the floral biology and pollination syndrome of Echinopsis chiloensis (Colla) Friedrich & G.D.Rowley (Cactaceae) in a population of semiarid Chile. Carmen G. Ossa and Rodrigo Medel, Gayana Botánica 68(2): 213-219, 2011. https://revistas.udec.cl/index.php/gayana_botanica/article/download/4415/4285/9172
How to prevent seedling damping off. Michelle Grabowski, University of Minnesota Extension, reviewed 2024. https://extension.umn.edu/solve-problem/how-prevent-seedling-damping
Propagation (chapter 13). North Carolina Extension Gardener Handbook, NC State Extension. https://content.ces.ncsu.edu/extension-gardener-handbook/13-propagation