For my potting mixture to germinate aloe seeds, I use a mixture of 50% river sand for good drainage & 50% compost/earth. Last year I got good results by putting the seeds on top of this mixture in small seed trays, cover with a fine layer of sand, soak in a tray of water and then leave in a clear plastic bag in the shade with plenty of light. This year I am trying some agave seeds as well (Macroacantha, Chiapensis, Havardiana, Bracteosa & Parryi v Chihuahua). Thank you John for starting me off with my first Agave, your Parryi from Arizona (now planted out).