SUMMER IS COMING – Install your Shade Cloth Above Your Grow Tables TODAY
– by Colle and Phyllis Davis
Plants can only utilize approximately 70% of direct sunlight. On the inside of a greenhouse, the temperature will rise very quickly as the sun climbs up into the sky. All greenhouses exhibit this rapid rise in temperature as the angle of the sun decreases. Even in very cold climates, the sun, on a clear day, can drive the temperatures from below freezing to the mid-60’s (15 to 20°C) very quickly. It most greenhouses, the problem is what to do with the heat and how to best utilize it for the good of the plants. Greenhouses are much easier to heat than to cool because the sun is the driving factor with the heat and that is tougher to regulate.
Shade cloth comes is a wide variety of blocking levels.
In installations using elevated medium (gravel in Portable Farms®) filled grow trays, the medium can very quickly heat up to killer temperatures for the plants if not protected from the direct rays of the sun. The advantages of the waist high gravel filled grow trays has to be tempered with the need to keep the gravel relatively cool. In raft systems, this problem is much less important because the light-colored ‘raft’ material does not heat up nearly as much as dark gravel.
Small plants growing in soil do not have much of a problem in full sunlight. The ground absorbs the heat and either passes it back to the air quickly or absorbs it lower into the soil itself. Even the lightest mulch will keep the soil cooler. With the use of gravel, the heat is absorbed and held in the top layer of unprotected gravel and this thin layer continues to heat up to over 140° F on a hot day. The seedlings will start to die if the gravel temperature exceeds 110° F for more than a few minutes.
This seedling stage of growth is the time the shade cloth is the most important in preventing the gravel from heating up faster than the air above it can remove that heat.