Find a sterile seed starting mix and cut it with 25% limestone sand to increase drainage. Fill your container two-thirds full with your mix and water in thoroughly.
Use a flat tool to tamp down the surface so that it is smooth.
Sow cactus seed evenly on the surface. Do not cover the seed (unless planting Opuntia spp). Sow during late spring and early summer for best results.
Place tray in partial shade and protect from afternoon sun. Use a misting nozzle to water in the cactus seeds after they are sown.
Keep soil moist by hand misting or with a misting system. After germination begins, feed once a week with fertilizer. Keep seedlings moist until winter.
Keep mostly dry during winter. Do not fertilize during cold weather. In the spring, you can transplant your cactus seedlings into individual pots.