SUMMER IS COMING – Install your Shade Cloth Above Your Grow Tables TODAY

SUMMER IS COMING – Install your Shade Cloth Above Your Grow Tables TODAY
– by Colle and Phyllis Davis

Note shade cloth mounted on the roof and sides of this greenhouse to protect the plants that will be planted in the gravel grow trays.

Note shade cloth mounted on the roof and sides of this greenhouse.

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.

Plants growing in a gravel medium in a Grow Tray in a Portable Farm.

Plants growing in a gravel medium in a Grow Tray in a Portable Farm.

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.


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    • Ronny on 2013-11-29 at 7:33 am
    • Reply

    A few questions.

    Water in our area is very hard is that OK to use?
    Can City water that has been chlorinated be used?
    We have only local rock (S E New Mexico) that is “Caliche” it is whiteish and softer than Limestone, Will it work in grow beds? I can buy imported rock if need be it just cost more

    Thank you

    1. Ronny,

      Hard water means it has a high mineral content, it will work fine. City water can be de-clorinated very easily, we tell you how in the Aquaponics University Course.

      Caliche will not work well its too soft. Everywhere in the world there is gravel available so choose limestone, basalt, granite or even crushed river rock.

      Good luck. We look forward to having you as a student in Aquaponics University.

      Colle Davis – Inventor

    • jim christison on 2013-08-24 at 10:56 pm
    • Reply

    Having just this evening found your website I have sat here and gone through many, many of your articles and have found your site to be the most helpful of any I have looked at even to the point of listing some youtube videos on processing the fish. Thankyou, thankyou, thankyou. But I have just read your article on shade cloth and would like to ask do you think there is an advantage to orientating your greenhouse east to west or sticking with the more traditional north to south. I am wondering about low levels of the morning/evening light against not shielding all of the east west house and allowing indirect light from the north side all day!? Yes I am in the northern hemisphere.

    1. Jim:

      Thank you for the kind words. You are too kind.

      The orientation of the greenhouse is dependent on latitude and climate. The further north the installation the more the long axis being east/west is important. It has to do with maximizing the available light and how best to insulate the building against heat lose. Shade cloth is necessary because full sunlight on the gravel will kill the seedlings. Movable shade cloth is the answer in colder climes.

      In most installations above the 35th parallel you will need grow lights to extend your grow day. Grow lights will give those installations a 20 to 25% increase in productivity and pay for themselves is less than two years. Tough to do this cost wise but well worth the installation cost.

      I trust this information is helpful to you.

      Colle Davis – Inventor

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