Growing Media for Greenhouse Crops
Growing Media Mixing Methods
The mixing process is one of the most important steps in the formulation of custom growing media; the best quality components are of no use if the growing medium is improperly mixed. Improper mixing is one of the major causes of variation in container plant quality. Incorporation of fertilizers and supplements must be considered too. Preparation of larger batches requires motorized equipment.
Continuous Mixing
In large greenhouse a continuous-belt mixing system is most common (Figure 12.13). Continuous mixing is accomplished by using material hoppers or feeder bins that layer material at set volumes onto a main conveyor belt located below the hoppers. The hoppers are large, 1- to 4-cubic-yard bins that dispense their contents, each holding one of the components of the mix (e.g., peat moss, perlite, or vermiculite). After the raw materials are layered, chemicals, nutrient charges, and other trace elements such as lime are also dispensed onto the belt. Each hopper is adjusted, either manually or automatically, to dispense its contents at a specific rate onto a conveyor belt. This belt deposits the media components into one end of a rotating drum to blend the mixture.
Pad or Skid Mixing
Pad or skid mixing is usually accomplished by layering the raw materials to be mixed on a concrete pad. A front-end loader is used to turn the material over and over, mixing the raw materials. Pad mixing is typically used at greenhouses that require only two or three different raw materials and because the consistency of the mix is not critical to the crops. Some of the growers using this type of mixed medium do so because it’s not critical to their crops to have an exact recipe.
Batch Mixing
Batch mixing utilizes a rotary-type mixer, such as a converted-cement mixer, or a drum and paddle type mixer. This method can be highly accurate when specific recipes are required. After the materials are placed in the mixer, the materials are tumbled or blended until consistency is achieved. Water is usually incorporated to prevent materials such as peat from breaking down or to correct the moisture content prior to filling the pot or cell pack. Depending on the type of batch mixer, cycle times for consistent blending will vary.
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