Growing Media for Greenhouse Crops
(book excerpts)Successful greenhouse production of container-grown plants is largely dependent on the chemical and physical properties of the growing media or substrate as it is often referred to. The word media is the plural of medium. The media should be well drained and yet retain sufficient water to reduce the frequency of watering. In greenhouse production, it is important that the substrate has good structural characteristics, so it can hold up to frequent irrigation, root growth, and temperature change over the life of the crop. At the same time, it must serve as a reservoir for water and nutrients and be able to allow air exchange between the root system and the aerial environment. Other parameters to consider include cost availability, consistency between batches, and stability in the media over time. Media is used to grow a wide variety of plants including vegetables, fruits, floriculture ornamentals, and specialty plants. Selection of the proper media components is critical in the successful production of plants. Today, growers can select from various components, including peat moss, vermiculite, perlite, rockwool, shredded coconut husks (coir), soil, or composted materials; and from various substrate additives to produce the substrates that best fit the needs of their crops. Because some of these individual substrates rarely have the optimal physical and chemical properties required when used alone, two or more are often blended together to produce a composite material that will have the appropriate properties for the crop being grown and the specific cultural conditions under which the substrate will be used. Substrate mixes are specially formulated for propagation, specific crops, or general use. Growers must be familiar with the positive and negative characteristics of the various substrates and how they will affect plant growth when creating a suitable growing medium, or even when purchasing a commercial mix.
Topics Within This Chapter:
- Properties of Growing Media
- Media Physical Properties
- Bulk Density
- Water-Holding Capacity
- Air-Filled Porosity
- Media Stability
- Media Chemical Properties
- Cation Exchange Capacity
- pH
- Electrical Conductivity
- Carbon-to-Nitrogen Ratio
- Growing Media Components
- Organic Media Components
- Peat
- Shredded Bark
- Pine Bark
- Hardwood Bark
- Coir
- Sawdust
- Rice Hulls
- Soil
- Animal Manure Composts
- Inorganic Media Components
- Vermiculite
- Perlite
- Calcined Clay
- Sand
- Polystyrene Chips
- Rockwool
- Common Media Amendments
- Limestone
- Application Rates
- Iron Sulfate, Aluminum Sulfate, and Elemental Sulfur
- Wetting Agents
- Formulations
- Fertilizers
- Biological Control Agents
- Grower-Mixed Media versus Commercial Media
- Commercial Media
- Grower-Blended Media
- Advantages of Soilless Mixes
- Growing Media Mixing Methods
- Continuous Mixing
- Pad or Skid Mixing
- Batch Mixing