How to Grow Cactus From Seeds
I was in last week and bought a few things to start out growing cactus from seeds. At you employees recommendation, I bought the small green seedling container, some coir, and some activated carbon. I put added the quite wet (but not soupy) coir, added 20 or so seeds to various spots, and then covered in a pretty fine layer of pulverized carbon (used a pestle and mortar). It is now sitting in out bubble window with the other plants. The lid is on and the humidity inside must be at 100% or close to it. Since I only have the seeds I put into this container, any other ideas for carefully germinating my seeds and not losing them to some other competitor would be IMMENSELY appreciated. That includes things like extra supplements, additives that modify PH, or anything that would be beneficial.
Cactus seeds like warmth to germinate, I try and get the temp up to about 80-85 degrees. You do need to watch that the seed dome is not in direct hot sun, or it could get too hot and cook the seedlings. The humidity is good to help break the seed’s dormancy, but do lift the lid now and then to give them some fresh air. Cacti can take a few weeks to even a year to germinate so be patient. After you see little green things that look like transparent green candy rice grains poke a few holes in the plastic lid to let in more air. As it starts drying out faster with the air, you will need to mist occasionally. Watch for mold and algae, though that is why you were told to use the charcoal, but in humid environments it can always be a problem. A low strength mist of Neem Oil usually takes care of it if it does cause problems. Plan on leaving the seedlings in there for about a year, though once they get some size and spines you can wean them off the humidity dome.
Good luck and happy growing.