Shade House

A shade house is a frame of posts carrying loosely woven cloth over a growing bed or a bench of pots. The cloth filters sunlight rather than blocking it, so whatever grows below takes a reduced share of the light and heat. Nothing is enclosed: no foundation, no glass, no heating or cooling gear. That makes it the simplest kind of crop shelter, and one hand tools will raise. The same cloth is often thrown over a greenhouse frame instead, and young plants are eased into full light beneath it before planting out.

How much light the cloth holds back is the whole design decision, and the crop sets it. For summer vegetables the useful band is about 30 to 45 percent shade. At 30 percent the sunscorch that marks exposed fruit and leaves becomes much rarer with no loss of yield; at 50 percent many crops grow soft, pale and late, simply short of light. The air underneath cools only a little, around 3 to 5 C (6 to 9 F), so it nudges a crop back inside the temperature it can bear rather than cooling a hot place; it replaces neither watering nor a heat-tolerant variety. Where a crop was already struggling that margin counts: shaded tomatoes have out-yielded unshaded ones by about a third.

The cloth is meant to come off. It goes up once the air under cover runs at about 27 to 29 C (80 to 85 F) and comes down as the season cools; left up, it grows the next crop in gloom. A stretched panel is a sail rather than a roof, and wind is what usually wrecks one; post depth and anchoring matter more than timber strength, and tears begin where the cloth is fastened. Mesh walls added to keep insects out also still the air, and still air brings disease. Sunlight breaks the fibres down: a stabilised mesh lasts at least five growing seasons, a light uncoated cover one to three; the frame outlives several cloths. Store it dry and away from mice, re-tension after storms, check the fixings.