Greenhouse Media Review What is the difference between Greenhouse Media and Mineral soil? The four functions of a media are: Provide support Provide air Provide water Provide nutrients Which 3 key properties (characteristics) did we look at in class? 1. physical 2. chemical 3. biological What is the difference between Stability and Support and why is each important? Stability - decomposes slowly and resists compaction Support - dense enough to hold the plant up and anchor the roots Why should total porosity of Greenhouse media be higher than that of Mineral Soils? Smaller depth less drainage more water holding List the 4 Chemical characteristics of greenhouse media 1. CEC 2. pH 3. low soluble salts 4. buffering capacity In order for your media mix to accomplish all four of the media functions, we must ensure that we do not overwork the components when mixing. If we do over mix, we could interfere with the large pore spaces called _macro pores. If this happens, there will not be enough _air___ for good root development. The small pore spaces in the media are known as capillary pores_, this is where _water__ is held in the media. A good greenhouse media will have between _75__and __85__% pore space. This is known as _total porosity_ The acceptable pH for a greenhouse media (generally speaking) is 5.5__ to _6.5__. This allows maximum nutrient availability . Buffering capacity is a media’s ability to resist change in pH. Sanitation in the greenhouse is vital. As a result, it is important to make sure that we buy components that are clean (out of the bag). It has been proven that beneficial microorganisms aid plant development both in the Nitrogen cycle and water intake. Components not purchased in a bag should be tested, and (especially in the case of field soils) pasteurized to kill pathogens . Our media components also must be as uniform as possible for easy and consistent reproduction, as well as economical and as ethically sourced as possible. Go through each component and amendment that we discussed in class and list the definite benefits as well as any drawbacks. For example: Peat Moss: Positives: High CEC, Water holding capacity. Addition of Organic Matter. Very stable. Adds dB. Brings down alkalinity. Inexpensive. Canadian Product Drawbacks: Large variation in pH (very low). Less - non renewable. Environmental impact of harvesting is high. Mineral Soils: Coir: Perlite: Vermiculite: Rice Hulls: Sand: Rockwool: Biochar: Wetting Agents: Trace Elements: There are a number of amendments that will be added to the basic components of this mix. We will add two different types of lime that will help to raise the pH of the media to enhance nutrient availability. The first one is Calcium Carbonate or Ground Lime, it is less expensive and faster acting, supplying calcium while adjusting the pH as soon as it is added to the media. The second type of lime is Dolomitic Lime, it is more expensive, and initially slower acting, but lasts longer in its effect on media pH. We will also add a very small quantity of another powdered substance. This amendment will supply all nutrients that are required by the plants during its time in the greenhouse.