Shade Houses and Potting Soils

warren glover 

November 2000

Allow me to list a couple of principles concerning shade-house growing and potting media. 


Firstly, the shade-house: A concrete floor is easier to clean, keep clean and to disinfect. The concrete stores heat in winter during the day and radiates it at night. Hiding places for pests and unwanted plant-growth are largely eliminated. This puts you way ahead of a cinder/scoria/aggregate or simple earth floor.  Exposure to sunlight is a crucial factor for Clivia and I have found that the 90% shade-cloth on my shade-house is suitable. Shade-house furniture is of a less crucial factor but I find the galvanized steel mesh and frame allows maximum air circulation which must be an important feature of all shade and glass-houses. 

Potting mixes 

Potting mixes are as variable as micro-climate, macro-climate, type of pot, availability of various ingredients and your storage facilities, type of nutrients you expect to use and finally your gut feeling from experience. The major factors to be considered in a potting mix's suitability are of course drainage, porosity and storage capacity of particles (this applies not only to liquids but to air and oxygenated gases generated by micro-organisms). Two basic types of media provide the above: A single unadulterated medium similar to those used in hydroponics-type culture from a coarse large particle-sized sand, or a larger particle-sized aggregate or larger scoria-type product or a mixture of each. The distinguishing factor is that there are NO ORGANICS. All the liquid that the plant receives (apart from precipitation) is a suitable nutrient solution. In this method the micro-organism population is extremely sparse so that the harmful ones are virtually eliminated. The other basic medium is a mix of organic and inorganic, virtually copying the medium of the plant's habitat. With this you have the teeming population of good and bad micro-organisms. Keeping the bad ones at bay requires special nutrient formulae that discourages the baddies. Refrain from using any nutrients that contain AMMONIAC compounds. These compounds promote the growth of harmful bacteria and fungi. Calcium is used in large quantities by bulbous plants and is crucial in developing disease resistance. CaNO3 is water- soluble and easily taken up by the roots and should be given to bulbous plants regularly as a drench during the growing season. Because of the different potting media no hard and fast rule on solution strength can be given but it is always better to be a weaker than stronger solution.