to hydroponics often ask what the best growing medium is. And
the truth is that there is no one "best" medium.
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.
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
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
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.
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.
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?
New Tool Co.
Reprinted with permission.
Workshop - Hydroponics - Cryan Studio
© Copyright 2005-2009 Fabric Workshop
P.O. Box 204 Centerbrook, CT 06409
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