Fill a pot with a moist, gritty, loam-based compost. Gently firm down and level the surface. Scatter your seeds over the surface, taking care not to sow them too thickly.
Gently sprinkle a thin layer of vermiculite or fine grit over the seeds, covering the whole surface of the compost. Leave the pot in a greenhouse or on a warm windowsill, covered with a clear plastic bag to preserve soil moisture.
Seedlings will develop within a few weeks. Remove the plastic bag and water when the compost becomes dry, but spray the surface with water regularly, to keep it moist.
The following spring, your seedlings should be ready to transplant. Use a fork or spoon to gently tease out the individual seed, taking care not to catch the spikes on your skin.
Part-fill a small pot with gritty compost and gently ease the cactus seedling into place. Use tweezers to ensure the seed is not sitting at an angle.
Fill around the seedling with compost and water well. Add more compost if necessary and then use the spoon to arrange gravel around the seed. Keep in a sunny spot such as a windowsill, and pot on as and when you need to.