Most cacti are easily grown from seed - and with a little patience and care they can be grown into beautiful plants.
Lophophora williamsii seedlings (VM 534k; El Oso, Coahuila, Mexico)
I'm growing my Lophophora, Obregonia, Acharagma, Ariocarpus and Strombocactus in more or less the same way (Strombocactus being the exception).
Till now I've used a finer compost for sowing but this year I decided trying to sow in the same growing medium I'm using for my mature (limestone-loving) plants, i.e. equal parts of:
- Coarse, loamy sand
- Limestone gravel
- Milled sphagnum moss peat
The seeds are placed individually (using a moist toothpick) directly on the surface of the compost and not covered. The pot is then sprinkled lightly with water and placed in a plastic bag with a bit of water at the bottom. Finally the bag is sealed closely and placed in a heated windowsill.
Hardening off seedlings
When most of the seed have germinated and the seedlings are well established it is time to introduce them to the harsh world (usually 4-5 weeks after sowing - but Strombocactus should be left considerably longer). This is done by puncturing the sealed bag to make the “atmosphere” less humid. The punctures are gradually expanded until the bag can be completely removed after 1-2 weeks. Until the roots are well established the seedlings must not be left dry for extended periods - this winter I almost killed off last years stock of Lophophora fricii seedlings by leaving them dry for 5 weeks!
The British Cactus and Succulent Society has a page on how to grow cacti and other succulent plants from seed. Steve Brack's Mesa garden has a list of basic germination tips.