Hydroponic Media

Hydroponics grows plants without soil, but those plants need something for their roots to hold on to and to retain moisture in between watering cycles. Growing medias are inert and will not grow anything without the addition of water and nutrients.  Here are some of the more common hydroponic growing medias:

Rockwool

Rockwool is composed primarily of granite or limestone which has gone through a special process in which it is melted and spun into long fibers.  It is then turned into blocks, cubes, sheets and other forms.  It absorbs moisture but doesn’t hold nutrients very well, and even when saturated will still allow air to reach your plant’s roots.

Rockwool does have its disadvantages.  Since it is made of rock, the fibers will last nearly forever when disposed of.  They usually come with a high pH and need to be soaked for some time before using.  The dust and fibers from rockwool can be harmful to eyes, noses and lungs.  You can keep the dust down by soaking the rockwool in water as soon as you take it out of the package.

Perlite

Perlite is composed of minerals which have been subjected to intense heat, causing them to expand and become absorbent.  Perlight is lightweight, is very porous and has a neutral pH.  It is popular in hydroponic systems because of its ability to hold moisture, nutrients and air.  It is inexpensive and easy to find at your local garden center.

Because perlite is so light weight, it can float on top of the water or nutrient solution and, especially when dry, can blow away under a strong breeze or fan.  When used by itself, perlite may not be able to support the weight of a plant, so it is often combined with other medias.

Vermiculite

Vermiculite, much light perlite, is a mineral that has been heated until it expands.  It retains more water than perlite and can wick water and nutrients upward.  It is often combined with other types of media.

Coconut Fiber/Coir

Coconut fiber (also called coconut coir) is the first organic hydroponic media to provide high performance in modern hydroponics.  It can be combined with other medias to increase water holding capacity.  Coconut fiber is pH neutral and holds more oxygen than rockwool.

Coconut fiber is available in compressed bricks which, when soaked in water, expands to about six times the compressed size.  Coconut fiber can be used as 100% of your growing media, though many growers find a 50/50 mix of coconut fiber and expanded clay provide a great growing medium.  Coconut chips are also available which are the same thing in a larger size, so they don’t fall through openings in growing baskets.

Lightweight Expanded Clay Aggregate

Lightweight expanded clay aggregate (LECA), is a media of small clay balls that have been fired at high temperature to create a porous media.  It is heavy enough to support large plants, holds moisture and has a neutral pH.  It can be cleaned and reused many times and is recyclable.

LECA does dry out quickly, so it may not be suitable for an ebb and flow system.  It is also quite heavy compared to other medias.  It can also be a little difficult to find, but can be purchased online.  The most popular brand of LECA is Hydroton.

Which is Best?

Which growing media is best depends on the type of hydroponic system you use and the type and size of plants you are growing.

It is easy to control moisture levels in a drip system as long as it is designed with good drainage.  Many people will add some pebbles or rocks to the bottom of the growing container to promote drainage and to prevent the growing media from sitting in a pool of nutrient solution.

Nutrient film technique systems usually use small starter cubes or small baskets with only a small amount of media in it.  If the cubes or baskets are too close to the nutrient solution flowing past the roots the growing media can become saturated, which could lead to stem rot and other problems.

Ebb and flow systems vary quite a bit in design.  Usually you want to stay away from lightweight media such as perlite or vermiculite, since the media will become essentially weightless during the flood cycles and the plants won’t have any support to hold themselves up.  Coco chips are popular for ebb and flow hydroponics, but good drainage is essential, as coco chips will wick up and remaining nutrient solution.

Deep water culture systems don’t use much, if any, growing media because the plant’s roots are submerged in the nutrient solution itself.  Plants are generally started in starter cubes or small baskets with a small amount of media.  How much the growing media absorbs can make a large difference.  You don’t want the media to become saturated with nutrient solution.  It should be moist at the bottom but dry at the top.

Aeroponics also don’t use much growing media.  They are designed to allow the roots to hang in air while being misted with nutrient solution.  You’ll want to make sure the growing media doesn’t become saturated, much like with DWC systems, as this can lead to stem rot.

Do you have a favorite growing media or have questions about which to use? Leave a comment below!

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