Tomatoes in Perlite

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Tomatoes in Perlite
A Simplified Hydroponic System

By Dan Brentlinger
With more and more vegetable growers looking into soilless or hydroponic vegetable production, the need for a simple yet productive growing system has gained attention in recent years.
  Hydroponic growing systems are based on sterile, inert, and uniform growing media that serve as supports for a water-soluble nutrient solution. Commercial growers have traditionally used one of several hydroponic growing systems: the nutrient film technique, of media-based systems using peat mixes, rock wool, and sometimes even sand or gravel.
  Horticultural perlite has an excellent record as a propagating and growing medium. It has been used successfully in many applications as a supplement to various growing media for a variety of crops. Now, however, perlite is beginning to be used by itself as an ideal hydroponic growing media.
  Perlite is produced throughout the U.S., making it cost effective for growers. It can be used for two years, and then spread on farmland or sold to gardeners.

What is Perlite?
  Perlite is a volcanic glass formed when lava cools very rapidly, trapping small quantities of water. When the glass is crushed and heated to about 2120 degrees Fahrenheit, the trapped water vaporizes and puffs out the softened granules to form a white mineral foam.
  Expanded perlite is physically stable and chemically inert. The porous nature of the granules ensures a product that is light to handle, holds large quantities of readily available moisture, and has a very strong capillary attraction for water.
  Since it is free draining, it is also extremely well aerated. Its neutral pH, negligible nutrient content, and freedom from pests, pathogens, and weed seeds combine to make it an excellent growing medium for hydroponic culture.

Perlite Developed in Scotland
  Scottish growers actually brought the perlite system to commercial greenhouse growers. Its major development was one of the major achievements of the West of Scotland Agricultural College.
  Dr. David Hall, who played a major part in its evolution, considers the technique of using bags of perlite "the main development in growing systems over the last ten years." He says the main objectives in their original research and development program were to simplify systems, maximize yields, and reduce costs. Perlite accomplished all three.

How the System Works
  The perlite bag system is very similar in design to a typical rock wool system. It consists of opaque, white-on-black polyethylene bags that contain approximately one cubic foot of medium to coarse perlite.
  It is important that the poly bags be treated with enough UVI (Ultra Violet Inhibitors) to last two years since the perlite can be easily used for two, yearlong crops. Each bag, approximately 44 inches long and 8 inches in diameter, is sealed and designed to hold three tomato plants.
  Seedlings are started in mesh bottom pots filled with perlite. The plants are grown for four to six weeks before being placed into the perlite bags. Drainage slits are cut into the bags, about an inch from the bottom.
  A constant supply of nutrient solution is maintained in the perlite from the shallow reservoir created in the bottom of the bag. The water taken up by the transpiration process is rapidly replaced by capillary rise through the perlite from the reservoir in the bottom 1 inch of the bag.
  As long as this reservoir is maintained, which is quite simple, the moisture profile in the perlite will remain constant. Less frequent watering is required than with rock wool, and there is less need for leaching and excessive runoff.

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