Hydroponic Growing Media
Before starting an experiment you should first understand the different types of media to choose from for a hydroponic project.
The word hydroponics traditionally meant that one 'grew in water', but now everybody uses some type of medium. Media is used to give the plant something to anchor it's roots in as well as provide some water holding capacity.
The key is that a hydroponics medium should not buffer (hold back or lock up) any nutrient. We want the plant to have instant access to anything it needs, when it needs it. Saying that, some hydroponic media do have a small buffering capacity for micro nutrients.
If you choose to use media with low water holding capacity, you need to make nutrients available to the plant all day. This can be done by a passive wick system or by using an automatic watering system.
|
Inert Media |
No buffer |
W.H.C.* |
|
Rockwool |
made from melted volcanic rock spun into fibers |
High |
|
Glasswool |
made from melted and spun into fibers |
High |
|
Perlite |
made from heated crushed volcanic lava ore |
Low |
|
Foam |
polyurethane or polystyrene |
Medium |
|
Pumice |
made from crushed lava ore |
Low |
|
Volcanic Rock |
use in Hawaii |
Low |
|
Sand |
traditional hydroponic medium |
Medium |
*W.H.C. = Water holding capacity.
|
|
Other Media |
Some buffer |
W.H.C.* |
|
Clay Pellets |
baked expanded clay (also called clay rock) |
Low |
|
Vermiculite |
heated and expanded micaceous mineral (ala silicate); mostly used as seeding medium only |
Medium-High |
|
Coco Fibers (coir) |
husk from a coconut shell |
Medium-High |
|
Sawdust |
used by growers in Alberta, Canada |
Medium |
|
Gravel |
traditional hydroponic media |
Medium |
|
Rice Hulls |
mostly used as a potting mix amendment |
Medium |
|
Bark |
|
Low |
|
For classrooms |
|
W.H.C.* |
|
Shredded paper |
holds water, so why not? |
|
|
Shredded fabric |
used by vegetables growsers in Israel in the 1980's |
Medium |
|
Hay |
traditional hydroponic media |
Medium |
|
Small Lego blocks |
a replacement for clay pellets |
Zero-low |
|
Polymers (gel) |
a jelly-like chemical binding between water, CO2 and a tiny amount of ammonia (hydrophilic polyacrylam |
High |
If you choose to use media with low water holding capacity, you need to make nutrients available to the plant all day. This can be done by a passive wick system or by using an automatic watering system.
Nutrients basics.
Mineral nutrient elements are divided into 2 groups.
MACRO nutrients
|
Primary: |
Nitrogen (N) |
Phosphorous (P) |
Potassium (K) |
|
Secondary: |
Calcium (Ca) |
Magnesium (Mg) |
Sulphur (S) |
MICRO nutrients
|
Iron (Fe) |
Boron (B) |
Zinc (Zn) |
Copper (Cu) |
|
Manganese (Mo) |
Sodium (Na) |
Chlorine (Cl) |
Cobalt (Co) |
In addition to the above, plants need non-mineral nutrients (Oxygen, Carbon and Hydrogen) which they get from air and water. We will not go any further into nutrients at this introduction stage. However if you are looking for a source with more detailed information, there is a handbook that provides a very good explanation and practical guide:
Plant Nutrient facts for Hydroponics and How to make your own fully formulated plant nutrient. By Jim McGaskill sold by http://www.foothillhydroponics.com.
