Vertical Garden

A vertical garden holds the soil itself up off the ground. Plants root in fabric pockets hung on a wall, in a stacked tower, or in a sack stood on end, so the growing medium goes up with them. A trellis is a different thing: there the plant roots in the ground and only its stems climb. The point is rarely more food per hour of work. It is food at all, on a fence, a balcony or a paved yard that would grow nothing otherwise, at a height a person can reach without kneeling.

The plainest form is a sack of soil and manure, cheap to build from found materials, with a column of stones about 5 cm (2 in) across up its middle: water poured in at the top runs down that column to plants set through holes in the sides, and one sack can carry up to 50 kale plants or 20 tomatoes and give several kilograms of vegetables a month. Whatever the form, depth decides the crop - lettuce, radishes and scallions want at least 15 to 20 cm (6 to 8 in) of mix, carrots 25 to 30 cm - and water decides everything else. A small volume of medium, exposed to sun and moving air, dries fast: daily watering is the baseline and hot dry weather can ask for more. Water until it runs from the drainage holes.

Every watering carries nutrients out, so feeding is continuous rather than occasional, starting two to six weeks after planting, and the salts left behind mean the medium is eventually replaced rather than improved. It pairs with stored rainwater and a drip line on a timer, because the gap between watered and dead is a matter of hours and a vertical face gives no warning until the plants wilt. Confined roots make smaller plants and less fruit than the same variety in ground, and corn and large vining crops will not grow this way at all. Roots held clear of the ground are the least insulated of any garden, so where a freeze arrives the medium comes down or the planting is treated as annual.