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Growing Medium

sub·strate


/ˈsəbˌstrāt/

– the base on which an organism lives

 The word “hydroponic” traditionally meant that one ‘grew in water’, but now everybody uses some type of medium. Media, or medium, is used to give the plant something to anchor its roots in as well as provide some water holding capacity.

The key to this concept is that a hydroponic 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. That being said, some hydroponic media do have a small buffering capacity for micro nutrients. This allows for the use of beneficial microbes to assist in the transfer of nutrients to the plant.

If you choose to use media with low water holding capacity, you need to make sure nutrients are available to the plant at all times. This can be done by a passive wick system, an automatic watering system, or an active water circulation system.

Inert Media No buffer W.H.C.*
Stone wool 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  n/a Low

Comparing different growing media by Grodan

Soil or Hydroponics?

Why switch from soil/peat/coco to Grodan Rockwool?

You may be thinking to yourself, “I do pretty well in my potting mix, why would I want to switch to Grodan Rockwool?”  The answer to that question is a long one, as there are TONS of benefits to growing in rockwool instead of soil, coco, or peat.  In this “Sold on Soil?” section, you can learn about the many advantages of growing hydroponically in Grodan Rockwool.

Rockwool and Soil Mixes: “By the Numbers”

Before purchasing your future growing media, consider the following differences between Grodan Rockwool and soil or peat based potting mixes. By choosing to grow your plants in Grodan Rockwool you can save money, water, space and nutrients.

Grodan: Sold on Soil? by Grodan