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Unformatted text preview: 23 Root Media Principles Historical Perspective Amended, field harvested mineral soil , with some proportion of sand, silt and clay, was the most common growing medium for container grown plants until the late 1950s. Anyone learning greenhouse production techniques since 1970 has most likely not worked with anything but soilless media . One of the first reported uses of a peat and sand based medium for production of potted chrysanthemums was in a research report from The Ohio State University around 1930. The 15-year period from 1955 to 1970 is recognized as the time when concentrated efforts in Europe and the United States were made to replace container media consisting primarily of amended mineral soils with porous, blended media that could be consistently reproduced from batch to batch, location to location and year to year. The decreased availability of mineral soils, the increased use of herbicides in field crop production, the need for more rapid plant growth to shorten cropping time, and the need to lower production costs were just some of the reasons motivating researchers and growers to look for alternative media. Root Media A variety of materials can be mixed to provide root media for container grown greenhouse crops. Root media selection is easiest with a clear understanding of the properties and characteristics desired. Defining the properties and characteristics of root media for greenhouse crops from plugs to hanging baskets is best done by considering the physical, chemical and biological aspects of the root zone environment. These factors control water and nutrient availability and can be used to minimize runoff. Physical Properties The physical components of root media include air, water and solid proportions. The typical percentage of these three components in a six-inch pot of soilless medium are 10 to 20 percent solid, 20 to 30 percent air and 50 to 70 percent water. These levels exist after the medium has been well watered and allowed to drain. This contrasts with mineral soils in the field which are more like 50 percent solid, 25 percent air and 25 percent water after saturation and drainage. Not all the water is available to the plant. In mineral soils the water not available to the plant is less than 5 percent. In a soilless peat-based medium 5 to as much as 15 percent of the water is unavailable to the plant. 24 Container size determines the actual proportion of air and water. The amount of air and water held in a given root medium is a function of the height of the column of medium. The shorter the column is, the greater amount of water and the less amount of air. The taller the column is, the smaller the ratio of water to air spaces....
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- Fall '04
- Peat, root media