Complete Guide for Growing Plants Hydroponically by Jones Jr. J. Benton

Author:Jones, Jr., J. Benton [Jones, Jr., J. Benton]
Language: eng
Format: epub, pdf
Published: 2014-01-07T19:06:14+00:00

Chapter five: Rooting media

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Figure 5.1 Rockwool slab wrapped in white polyethylene sheeting with a rockwool cube placed on a cut opening in the sheeting.

Rockwool

Rockwool is a fibrous material produced from a mixture of volcanic rock, limestone, and coke; melted at 1500°C to 2000°C; extruded as fine fibers; and pressed into loosely woven sheets (Smith 1987). The sheets are made into slabs of varying widths (16 to 18 in. [15 to 46 cm]), normally 36 in.

(91 cm) in length, and ranging in depth from 3 to 4 in. (5 to 10 cm). The slabs are normally wrapped with white polyethylene sheets as shown in Figures 5.1 and 5.2.

Figure 5.2 A typical rockwool slab with rockwool cubes spaced as would be appropriate for growing tomatoes.

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Complete guide for growing plants hydroponically

The slabs are normally laid flat on a prepared floor surface, which is usually first covered by white polyethylene ground sheeting. Spacing among the slabs will depend on the configuration of the growing area and the crop to be grown. Once the slabs are set in place, cuts are made along the lower edge of each slab of the polyethylene slab covering on the bottom to allow excess nutrient solution to flow from the slab. An access hole is then cut on the top of the slab sheeting to accommodate a rockwool block containing a growing plant. Nutrient solution is then delivered to each rockwool cube by means of a drip irrigation system.

Rockwool is probably the most widely used hydroponic growing medium in the world today for the production of tomato, cucumber, and pepper, although efforts are being made to find an adequate substitute because disposal of used slabs is becoming a major problem. Rockwool has excellent water-holding capacity, is relatively inert, and has proven to be an excellent substrate for plant growth (Sonneveld 1989).

Coir

Coir is a natural fiber extracted from the husk of coconut—the fibrous material found between the hard, internal shell and the outer coat of a coconut (www.wikipedia.com). Coir is being recommended as a substitute for rockwool since it is an organic substance and can be more readily disposed of at the termination of its use as a rooting medium. Coir can be formed into blocks and slabs, such as those for rockwool, and used in much the same way.

Coir has much the same physical properties as rockwool, but it does contain both essential and nonessential elements— mainly sodium (Na).

Therefore, coir may require water leaching to remove Na if it is high and thus could affect plant growth.

Elemental content of perlite, rockwool, and coir

These three rooting media are derived from naturally occurring substances and therefore will contain some, or many, of the essential plant nutrient elements. What portions of these elements are “available” for plant utilization is not generally known, nor easily determined due to their varying parameters of use. Experience, however, would suggest that a portion of the contained elements in a rooting medium can be available for root absorption. How that determination is made is the challenge.

Samples of

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