- Start with a quality cactus soil for best results. It isn’t crucial for it to be cactus specific, a commercially available mix can be suitable. If you prefer to make a free draining well textured mix, 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. Sow the cactus seeds on the surface of the cactus soil. 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 total width. Adding holes to the bottom of the container is recommended if you’re worried about over saturating the soil and growing the cactus seedlings.The idea here is to provide a humid environment for the cactus seeds to germinate. Condensation on the inside of the container is normal. 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.
- Water the cactus seed soil 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. lace 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 20-30C (86F) range during cactus seed germination. This is important, 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.
The greatest proportion of cactus seed germination will occur in the first 2-4 weeks, this is when the strongest seeds will germinate in the greatest numbers. The cactus seedlings will continue to crop up occasionally in the coming months, though, at a decreased rate. By the fourth month it is safe to assume all seeds have germinated during the first cactus seed germination cycle. Those that have not yet germinated, often can during a second cactus seed germinating cycle (see below). Cautiously, maintain these humid conditions beginning to slowly acclimatize the cactus seedlings to normal environmental conditions by the first year of growth.
*Often times cacti require stratification, this mimics their natural growth cycle. If cactus 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 40%-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.