- Start with a quality cactus soil for best results. It isn’t crucial for it to be cactus specific. A commercially available mix can also be suitable. If you prefer to make a free draining well textured mix yourself, use; one part sand, one part heavy grit, and one part standard potting mix. The goal is to select ingredients with good drainage. Store bought cactus soils do not provide good drainage. if they are to be used the addition of grit would be necessary. Sift out any foreign particulate (rocks, sticks, etc) from the mix while filling your preferred seed sowing chamber.
- Try to select a container that has an opaque base and a transparent top to minimize the growth of algae. Fill the container about 3/4 full. There should be some room between the soil surface and the top of the container for air flow. Do not poke holes in the soil to bury cactus seeds. Adding holes to the bottom of the container is recommended if you’re worried about over saturating the soil. Alternatively, It is also possible to cover the pots used with plastic or polyethylene food wrap as or use food storage containers with lids. Find what works best for you; as long as humidity can be maintained.
- Sow the cactus seeds on the surface of the cactus soil. They can be sown a few mm away from one another. You can sprinkle a light layer of cactus soil over them when done sowing or also opt to use clean sand. The cactus seeds should not be buried any deeper than their width. The idea is to provide a humid environment for the cactus and succulent seeds to germinate in. Condensation on the inside of the container is normal.
- Water the cactus & succulent seed medium very lightly and seal the environment the cactus seedlings will be growing in. Aim is for a moist soil, not water logged soil. Once wet, try not to let the soil dry out. Place the cactus seed container in an area where there is no direct light, cactus seedlings are sensitive and will likely burn from high intensity light. Diffuse sunlight is ideal. Grow lamps can also work. If the seedlings turn red this means the light is to intense. If they begin to stretch, it means the light is to weak. Find a spot for you cactus seedlings where the light isn’t to bright or to dark. The light duration for germinating cactus seedlings should be 12 – 16 hours of continuous light per day.
- Aim for temperatures in the 20°-30°C (86F) range during the day. 25°C is ideal. This is important, and a thermometer is recommended. Too hot is equally bad, and will cook the cactus seedlings. If sealed properly the cacti seedlings will not need to be watered in these early stages for a number of weeks. More so, a bottom heater can be used to aid in cactus seed germination requirements. During the night the temperature should temporarily trend lower.
The greatest proportion of cactus & succulent seed germination will occur in the first 2 – 4 weeks, this is when the strongest seeds will germinate in the greatest numbers. Seedlings will continue to crop up occasionally in the coming months, though, at a decreased rate. Some varieties grow in spurts and can be inconsistent when germinating. By the fourth month it is usually safe to assume all seeds have germinated during the first germination cycle. Cautiously, maintain these humid conditions for three to six months, beginning to slowly acclimatize the cactus seedlings to normal environmental conditions by reducing humidity levels within this timespan.
Those that have not yet germinated, are often able to during a second germination cycle. Some cacti require stratification, this mimics their natural growth cycle. If seeds do not germinate the first cycle allow the cactus seed soil to completely dry out. Repeat steps 3-4. These steps will stimulate new cactus seeds to germinate.
It isn’t realistic to expect 100% of seeds to germinate. Cacti have variable germination rates. More over, batches of seeds within the species group will have varying degrees of viability. A practical expectation, if correctly executed is a 30%-80% average cactus seed germination rate. With some difficult species of cacti having even lower rates.
Most of all, be patient. Rushing these steps can lead to disappointments and delayed development. In the case of cacti seedlings, less is more.
Conophytum, Echeveria, Crassulacea, Lithops and Mesembryanthemum prefer cooler temperatures. They should not have temperatures above 20° C until they have germinated, thereafter they should also not be covered.
Dinteranthus requires up to 3 months to germinate.
Copiapoa benefit from frost exposure prior to germination.
Opuntia seeds with thick and hard seed coatings will benefit from scarification. This can be achieved by nicking or scratching the surface of the seeds with sandpaper or a file, then soaking in water overnight before planting.