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Hydroponic Growers
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Hydroponic Air Farms


Growing Media.

Folks new to hydroponics often ask what the best growing medium is. And the truth is that there is no one "best" medium.

There are characteristics to each of the most popular media that keep them popular. Though it is difficult to work with, perlite is still used by many of the commercial operations, being very cost effective and reusable. For home use, cost isn't really a determining factor, as the difference between perlite, clay pellets, cocopeat and rockwool in the quantities that we use is minimal.

Perlite is a volcanic rock that has been pulverized. It is white in appearance and abrasive to the touch. Perhaps it's for this coarseness that it is considered a potential carcinogen. Most often used in trench type greenhouse operations, this is often used in what is known as the bag method of growing. Though we don't recommend using it, great care should be used in handling this medium should you decide to use it. At the very least, you should use a particle mask and wash thoroughly after any contact exposure.

Rockwool is also a volcanic product, though in a much more stable form. It is spun into a glass wool and is used in a variety of hydroponic products. The most common of these is the rockwool cube. These may be shaped cubes with seed depressions in them and come in a sheet or they may be cubes with a paper coating that can be planted into succeedingly larger sizes. These can be used in conjunction with rockwool slabs in some larger systems. Rockwool may tend to lower the pH of your nutrient solution. Some hydrofarmers soak their cubes before using them to leach out some of the acidity. As the solution is naturally basic, it may save some pH Down by not doing so.

We use 1 ½" rockwool cubes for small seeded plants like most flowers and tomatoes and lettuces that we seed directly into the Air Farm (instead of transplanting). To speed germination, we add a little soilless potting mix or cocopeat into the seed depression in the cube and plant the seed into that as we would in any other pot. We wet the potting mix and cube and keep them moist throughout the germination period and even past the point when the roots have made it into the reservoir. Is this really hydroponic gardening? Yes, in that it is soilless and it combines two media to eliminate having to wash off the loose soilless mix from seedling transplants. It also eliminates the transplantation process.

Grorox are fired clay pellets. Some are shale based and some plain clay based, but both are inert and allow for air flow to the roots. These are the two most important characteristics of your growing medium. Grorox is a brand name for a product that may be called Leca stone or any of a number of brand names. It is a terrific medium for Air Farms in that it fulfills all of our requirements. It is inert because it doesn't react with the solution nor change its characteristics. It provides lots of airspace between the rocks. This is important for several reasons:
During period between generation and the time when the roots make it through the net pot, your roots will need moisture. As the Air Farm is a sealed system, the air pump generates a mildly positive air pressure inside the reservoir. This moist air escapes through the air spaces between the rocks and moistens your new roots. If you watch when you first plant your Air Farm, you'll see the rocks darken as the water moistens them. This will happen over a period of a few hours. Keep one stone dry to compare.

Cocopeat is a byproduct of coconut harvesting. A very clever use for the shells is to shred them and compress the fibers into a very stable brick. This otherwise unusable material makes an excellent medium for hydroponics. It degrades so slowly that it is reusable. After processing it is essentially inert. And it retains some water while providing ample airspace for the roots. Unfortunately it is too fine for our Air Farm pots, but it does have other uses including a substitute for soilless mix or peat, indoor gardening or as an amendment to small plots or beds of high clay soil. It will hold its properties much longer than peat and though more expensive than peat, it needs to be replaced or replenished less often. It also works well as a mulch and as a bed for berry plants.

For our Air Farms, we include Grorox which work well for large seeded plants such as peas and beans and as a support for transplanted seedlings or seed cubes. We've also used rockwool with great success for tomatoes, flowers and such small seeded plants.

One medium that I haven't mentioned is free, reusable and has no environmental impact. That is, of course stone. The original medium for hydroponics dating back thousands of years, stone is still used for such plants as orchids in the form of marble chips. But you can use stone directly from your driveway as long as you wash it in a mild bleach solution to rid any microorganisms that may foul your system.

The roots require air and moisture, especially during the critical earliest part of their cycle. So regardless of what medium you use, be sure to monitor your plants closely while they establish themselves. But there's no need to get neurotic over it, if you lose a seedling, it's not the end of the world. And you're doing this for enjoyment, not competition, right?

Copyright 2000
Glenn Rice
Air Farms
New Tool Co.
Reprinted with permission.


Growing Ideas


Fabric Workshop - Hydroponics - Cryan Studio
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