Defining the Medium Culture in Hydroponics
Hydroponics, which is the growing of plants without soil by
providing them with nutrients via water, can be accomplished in two main ways.
Solutions culture hydroponics is a technique where roots are exposed to water
on their own; the plants and the water are the only part of the hydroponic
system. In medium culture hydroponics, the roots are encased in some sort of
solid growth medium before they receive the nutrient water solution.
Medium culture hydroponics is somewhat controversial. Some
argue its effectiveness makes it the superior hydroponic system of growing,
above solutions culture. Others argue that the addition of a solid medium means
that the growth process is not hydroponic at all. These nay-sayers complain
that many of the growth mediums used actually supply some sort of nutrient to
plants, making them, in effect, just like soil. Whatever objections some might
have to using medium cultures in hydroponics, it is an extremely effective
technique that is growing in popularity.
Medium cultures work in two ways; passive sub irrigation and
top irrigation. Some mediums use one or the other, and some use a combination
of the two. Substances that use passive sub irrigation generally have large
spaces and gaps that allow oxygen to flow freely to the roots. A system of
capillaries in the growth medium draws the water and nutrient solution inside
and then circulates the nutrients to the roots. One variation of the passive
sub irrigation method is called flow and drain, or ebb and flow, irrigation. In
this technique, the plants and the growth medium are kept in a tray, and a pump
sprays the growth medium with nutrient solution and oxygen at regular
intervals. The growth medium then transports the nutrients and oxygen to the
roots.
In the top irrigation method, the nutrient mixture is simply
applied to the top of the growth medium. The medium then absorbs the nutrients
and supplies them to the roots, which are buried deeper in the medium.
Nutrients can be supplied using the top irrigation method as infrequently as
once a day, for small plants, or as much as 5 to 10 times an hour, if using a
pump to deliver the nutrients.
A wide variety of materials can be used as growth medium.
Each medium has its benefits and drawbacks, and some are better suited to some
plant types than others. Diahydro and expanded clay are two popular choices for
growth medium, but they also come in line for a lot of criticism because their
high silica levels supply the plants with additional nutrients. Rockwool is
perhaps the most popular growth medium, but is should be handled with care. The
particles in Rockwool can be dangerous to animals and humans if they are
inhaled when they are dry.
Perlite, which is a type of volcanic rock, is becoming
increasingly popular as a growth medium and may soon surpass Rockwool as the
top choice. Perlite does a great job of maintaining healthy moisture levels in
the roots while plants are growing. Vermiculite, another type of volcanic rock,
also works well. Other common growth mediums include coco coir, which is the
fiber from the husks of coconuts, sand, gravel, brick shavings, and even
polyurethane packing "peanuts."
Which growth medium you should choose depends on what plants
are you are growing, and how large scale your operation is. Amateur growers may
want to start out with inexpensive choices like sand or gravel, while larger
scale farmers may find the reliability of perlite makes it the ideal choice for
them. Despite the controversy, growth medium cultures are not likely to go away
any time soon in hydroponics.
