I don't use the clay-base soil around here, I've killed some high dollar strains with that shit. I use 60% mushroom compost, plus vermiculite,, perlite, peat moss, worm farm dirt and a few cubes of shredded rockwool. I use a 5 ft. Kiddie Pool to mix the shit up. Sterilized cow manure is really good. (Black Kow). Lady Bug products is a trusted product. With this dry mix, I add diluted fish emulsion, whole ground cornmeal, liquid seaweed, molasses, Epsom salt & green sand. A metal fence post will grow in this shit. Check out your local Nursery for soil to grow "Tomatoes In Your green house." The cornmeal, Epsom salt & molasses is at the grocery store. Good Luck. BTW, if you could get some rabbit manure from a local rabbit raiser, you would do well to get some- 60% of total soil.