My first hardy cacti will be arriving soon for planting in troughs, and I'm unclear about the planting medium. I think I'm OK with the base of 1/3 each loam, coarse sand, and crushed gravel 1/4"-3/4", but John Spain's booklet calls for 1-1/2" of 1/2" gravel as top dressing on all substrates in all situations. He says "Cactus plants that are not seedlings or weak cuttings will send their roots through a layer of this kind that is up to 4 inches deep."
Maybe it will be obvious to me when the shipment arrives and the plants will have thick 6" roots, but I thought I should try to find out beforehand.
Am I right in thinking that he is calling for me to perch the plants up on top of 1-1/2" of pure gravel, far away from any moisture-retentive medium, and that will be OK? Perhaps they're like Weebles and they won't fall down? Or they just root wherever you set them?
I guess I need to go crush more stone. I wonder why 1/2"?
