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GROWING MEDIUM

by Professor Hydro

There are probably hundreds of different kinds of growing medium, anything that a plant can grow in is considered a growing medium. There are manmade as well as organic (natural) mediums. Even plain old AIR can be an effective growing environment for roots.

I have been asked many times what growing medium is the best. This is like asking what is the best color? Or what is the best kind of vehicle to own. Sometimes the answer depends on the job you need it to do. You wouldn't try to use a soiless mix in an Aeroponic system and you don't plow a field with a Rolls Royce limousine. However, if you want to build a Non-Recovery Drip hydroponic system then the soiless mix would be an excellent choice, and a John Deere tractor can handle the field (save the Rolls for a night on the town, pick me up at 8). What I'm trying to say, is that the best growing medium for your purpose depends on many variables. The type of system you are using, what kind of crop you are growing and local environment are just some of the many determining factors involved when choosing a growing medium. There may be several mediums that will work equally well for your particular needs. Many times it boils down to availability, price or personal preference.

I have listed the most popular types of growing mediums below, click on the name to view details about the general use, advantages and disadvantages, and particular characteristics of the specified growing medium.

Oasis cubes Expanded Clay Pellets Rockwool
Coconut Fiber Sand Gravel
Perlite Sphagnum Moss Water
Vermiculite Fiberglass Insulation Saw Dust
Soilless Mix(s) Air Lava Rock


Oasis cubes

These lightweight pre-formed cubes are designed for propagation. A very popular medium for use when growing from seed or from cuttings. This product has a neutral pH and retains water very well.

The cubes are meant to be a starter medium and come in three sizes up to 2" x 2". They can be easily transplanted into practically any kind of hydroponic system or growing medium (or into soil).



Coconut Fiber

Coconut fiber is rapidly becoming one of the most popular growing mediums in the world. In fact it may soon be THE most popular. It is the first totally "organic" growing medium that offers top performance in hydroponic systems. Coconut fiber is essentially a waste product of the coconut industry, it is the powdered husks of the coconut itself.

There are many advantages - it maintains a larger oxygen capacity than rockwool, yet also has superior water holding ability than rockwool which is a real advantage for hydroponic systems that have intermittent watering cycles.

Coconut fiber is also high in root stimulating hormones and offers some protection against root diseases including fungus infestation. Dutch growers have found that a mixture of 50% coconut fiber and 50% expanded clay pellets is the perfect growing medium.

One word of caution about coconut fiber, you must be careful when you purchase coconut fiber. There is a commonly available, lower grade of coconut fiber that is high in sea-salt and is very fine grained. This lower grade coconut fiber will lead to disappointing results when used in a hydroponic system.



Perlite

Good old perlite! It's been around for years, mainly for use as a soil additive to increase aeration and draining of the soil. Perlite is a mined material, a form of volcanic glass that when rapidly heated to more than 1600 deg. f. it pops much like popcorn as the water vaporizes and makes countless tiny bubbles.

Perlite is one of the best hydroponic growing mediums around. Used by itself or as a mixture with other mediums. Perlite is commonly used with vermiculite ( a 50 - 50 mix is a very popular medium), and is also one of the major ingredients of soiless mix's. perlite has good wicking action which makes it a good choice for wick-type hydroponic systems. Perlite is also relatively inexpensive.

The biggest drawback to perlite is that it doesn't retain water well which means that it will dry out quickly between waterings. The dust from perlite is bad for your health so you should wear a dust mask when handling it.



Vermiculite

Vermiculite is another mined material. In it's natural state it resembles mica rock, but when quickly heated it expands due to the generation of interlaminar steam.

Vermiculite is most frequently used in conjunction with perlite as the two complement each other well. Vermiculite retains moisture (about 200% - 300% by weight), and perlite doesn't so you can balance your growing medium so that it retains water and nutrients well but still supplies the roots with plenty of oxygen. A 50/50 mix of vermiculite and perlite is a very popular medium for drip type hydroponic systems as well as ebb and flow systems. Vermiculite is inexpensive.

The major drawback of vermiculite is that it retains too much water to be used by itself. It can suffocate the roots of plants if used straight.



Soilless Mix(s)

There are many kinds of soiless mix's containing a vast assortment of ingredients. Most contain things like Spaghnam moss, Perlite and Vermiculite.

These kind of growing medium are usually considered organic and are frequently used for container gardening wick systems and on-recovery drip systems. They can be used in recovery systems, however most of these mixes have some very fine particles that can clog pumps and drip emitters if you don't use a good filtration system (NOTE: The professor says that you can use panty hose as a filter, use on the return line and on the pump inlet to filter out the fine particles).

Most soiless mixes retain water well and have great wicking action while still holding a good amount of air, making them a good growing medium for a variety of hydroponic and organic gardens.

Hydroponics University

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