Total-control Indoor Gardening with Modern Hydrop

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In hydroponics, none of these natural stresses occur. A plant will grow just enough root to keep its stem immobile and will generate the minimum of feeder roots needed to absorb food—the nitrogen (N), potassium (K), and phosphorous (P) that are familiar to gardeners ... as well as a dozen or two other minerals. In hydroponics, the plant doesn't have to extract nutrients from surrounding soil minerals; a balanced diet is provided in ready-to-absorb form in its nutrient bath. But every agitation of the stem will encourage unneeded root production; the plant's base must be firmly supported from the day the seed sprouts.

FRESH TOMATOES AND
CUCUMBERS ALL WINTER LONG, In
two months less time, Lettuce in just
four weeks

Peat moss, sawdust, wood chips, chipped bark, sand, gravel and crushed rock, gardener's heat-expanded mineral soil conditioners (such as perlite and vermiculite mixed with sand), expanded clay pellets, and other chemically stable media are used as hydroponic rooting media with varying degrees of success. Coarse sand is most popular where it's most abundant, in desert areas, and works adequately. Sawdust (most commonly used in logging country) and peat do not drain well and can waterlog and rot. Both are naturally acidic. Some gravels contain limestone that will bias pH; they can contain soil, decayed vegetation, and plant pathogens as well. The manufactured soil conditioners are sterile, pretty much pH—neutral, and all-natural; perlite consists of little white popcorn-like puffs made by heat-expanding a volcanic rock that is high in silica; vermiculite is made much the same way from mica. Very lightweight, they will blow around when dry and can waterlog. They also break down relatively quickly.

Presenting none of these problems, and widely-used for small cuttings and seedgrown plants, is rockwool: fibers spun from melted natural rock minerals and formed into a mat or blocks. Introduced to North America from Holland as recently as 1985, horticultural-grade rockwool is made from virgin basalt rock (hardened volcanic lava) that is mixed with a limestone flux and melted to 3000°F in a coke oven, much as steel is made from iron. The (re-)molten lava is then spun out into thin fibers that are coated with a separating/wetting agent, bundled with strands parallel and vertical, and pressed into mats or cubes in several sizes or sold loose as flock.

Inch-square seedling-size cubes with a seed pit in the center come 98 to a 10" x 20" block that fits perfectly into a standard propagating tray. "Gro-squares" are 4" cubes that have a hole in the middle to accept a seedling cube. Some brands are enclosed in a thin paper sheet to keep algae from growing. At less than a dime apiece for the inch-size and 50¢ for the 4"-square size, rockwool is cheaper than those little compressed- peat- in -plastic—mesh discs or than a plastic pot and potting -soil mix. Created at a rock-melting temperature, rockwool is sterile, so cannot introduce weed seeds, mold spores, or pest organisms. Unlike slag-based insulating rockwool, it is pH-neutral and chemically inert. Best of all, it is over 90% air, and its fibrous structure draws in water quickly by capillary action. Most of the water drains out quickly as well, keeping roots moist but preventing water logging. Blocks can be separated slightly in the nutrient solution so roots will self-prune. Then roots of adjoining seedlings won't intermingle and be lost when plants are separated. After harvest, you can gently pull old roots from wet cubes, boil or steam, and then reuse them till they wear out. Grodan is a popular brand, manufactured in Denmark, England, and Canada. A dust mask and gloves are recommended to handle loose rockwool flock, as it can be an irritant. Though rockwool is widely available in the U.S. through virtually every hydroponics mail order company, it is not without its detractors. The runoff from daily rockwool use as well as its disposal have been suggested as culprits in groundwater contamination in Europe and its use is actually in decline there.

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