Hi Allan - Here is the excerpt on sand from the publication itself. I think it explains it pretty good and brief. I once made the mistake of purchasing fine sand for greenhouse production instead of course sand, and you definitely want the course type for improved drainage etc.
Want to try something interesting with potting mixes? See my slides on organic greenhouse vegetable production; starting on about slide 43 is the shallow bed method of production for raising sprouts in a greenhouse and for produciing transplants outdoors; i.e., those are Russian farmers laying plastic on the ground, it is then covered with about 3 inches of a manure or compost-based potting mix, then seeds are sown via dribble or broadcast; thus you can raise thousands of bare root transplants in a small area without the hassle of plastic plug trays to one day dispose of; a secret revealed, though not commonly done, is that you can also raise certain crops to maturity and never transplant out of the shallow bed; e.g., lettuces, greens, beet tops, etc... and if you stake the plants up, you can also do shallow bed production of tomatoes, peppers, and cukes; altogether, an intensive method of production in a small space. I believe the Russian farmers used aged manure, sawdust, and sand. Wood is an abundant resource up north, and sawdust was commonly used in potting mixes / shallow bed mixes. In my view, a geotextile weed barrier would make a nice ground cloth as an alternative to plastic mulch; thus, another use for super low-maintenance weed barriers in agriculture. Organic Greenhouse Vegetable Production slides [2960K PDF] http://ncatark.uark.edu/~steved/ogvp-print.pdf Interestingly, the Russian farmers were *totally* into the Mittleider method; one of the farmers had attended a Mittleider workshop and that is how they went about organizing their approach to just about everthing: bed production, plant spacing, fertilizing, greenhouse design, etc. They were doing truck farming on a 6 bed + drive row + 6 beds pattern making up about 10 acres, and those shallow-bed-raised-bare-root transplants were hand transplanted into the field using a marker stake to set out twin rows of broccoli, cauliflower, beets, etc. If you live in Alaska, on a parallel lattitude with Russia, you know that selection of crop variety adapted to *long* daylight conditions is critical; otherwise the cole crops will button, and that sucks more than a elephant getting a drink of water after a hot day on the Zambezi Plains. A garden rake, perfectly sized in width, was used to create a well in the center of the bed running the full length of the field, thus creating a grow bed and also to create a reservoir for irrigation. So the Mittleider method goes beyond soilless grow boxes, which is what you get by looking at books like "More Food From Your Garden," though I know a few hoop house farmers who still find those books doublely inspiring as an early model of hoop house production. The Mittleider Method -- Food for Everyone Foundation http://www.growfood.com Best, Steve Diver Excerpt from "Organic Potting Mixes for Certified Production" Sand. Choice of sand in a growing mix can make a difference. Coarse sand -- called builder's sand -- adds air space to the potting mix. Fine sand settles into the spaces between other ingredients and makes a dense mix that tends to exclude air. Clean, washed sand has a near-neutral pH and little if any food value for plants. Sand is much heavier than any other ingredient used in potting mixes. The added weight is good for tall, top-heavy plants that might blow or tip over, but it is not the best choice for plants that will be shipped or moved a lot. Sand is the least expensive and most readily available larger particle material.
