Hydroponic Growing Media
Hydroponic growing media, or medium, is any suitable inert substance that supports the roots or stalk of a plant without providing any substantial nutritional value to the plant.
Fired Clay Pebbles
Fired clay pebbles are a hydroponic growing media derived from common clay, and are considered an ecologically sustainable growing medium. The clay is formed into round or irregularly shaped pellets and fired in rotary kilns at temperatures up to 1200 degrees Centigrade. The extreme heat causes the clay to expand and become porous, as well as completely sterile. Also known as grow rocks, expanded clay pebbles, and Lightweight Expanded Clay Aggregate (LECA)®, fired clay pebbles are lightweight, do not crush or compact, and are clean and reusable with rinsing. Most fired clay pebbles are pH neutral and completely inert for precise nutrient control in hydroponic applications. They drain freely and do not hold excessive amounts of water, providing excellent oxygen levels at the root zone. They are widely used in greenhouse cut rose cultivation and embraced by many professional orchid growers.
Coir Fiber Coco Peat
Coir fiber, coco coir, or coco peat, is a bi-product of coconut husks where the long fibers are separated from the husk. Used as a hydroponic growing media, it is an entirely renewable organic resource that provides increased efficiency of water use, superior root zone characteristics, and works well with both organic and elemental plant foods. Coir dust is rinsed, heat sterilized, graded and screened prior to being manufactured into various coco peat products for many botanical applications. First used as a growing medium in England more than 140 years ago, cocopeat is a multi-purpose soil amendment and soilless container growing medium that is also popular in hydroponic applications. It has a consistent and uniform texture composed of tiny capillary sponges that hold as much as eight times their weight in water. The typical pH runs between 5.5 and 6.5 and the 30 to 70 percent air to water ratio provides assurance to growers that coir will store and release nutrients over extended periods with less frequent irrigation.
Growstone Hydro Stones™
Growstone Hydro Stones™ are a hydroponic media that is manufactured using finely ground recycled glass. After the glass has been pulverized to a powder consistency, it is mixed with calcium carbonate and fired inside a kiln. As the glass particles are heated, they fuse together and create air spaces in the glass. After fusing, what remains is a lightweight, expanded material that is broken into the desired size pieces after it cools.
Not only can Growstone Hydro Stones™ be used as a stand-alone hydroponic growing media, it can be mixed into potting mixes of many varieties to improve drainage and oxygen levels at the root zone.
Perlite is a volcanic mineral expanded from four to twenty times its original volume after it is heated to a temperature of around 1600 to 1700 degrees F. The expansion is a result of the presence of between two and six percent water contained in the raw perlite rock, causing the perlite to explode like popcorn. Each resulting granular, snow-white piece of perlite is sterile with a neutral pH and contains many tiny air pockets. The surfaces are covered with microscopic pockets which hold moisture and nutrients and make them available to plant roots.
As a result of the manufacturing process, air passages are formed which provide optimum aeration and drainage. Due to the high temperatures used, it is completely free of weed seeds, dormant diseases, or destructive insect pests. Perlite has long been used around the world a soil amendment or as a popular component of soilless growing mixes. Perlite’s unique capillary action and ease of sourcing makes it a popular growing media for hobby hydroponic applications, and is now available in large bags of coarse perlite and super coarse versions specifically for soilless applications.
Coarse sand for horticultural applications is generally defined as sand with a diameter between .5 and 1 millimeter (.02 and .039 inches), whereas medium sand has a diameter between .25 and .5 millimeters (.010 and .02 inches), and fine sand between .125 and .25 millimeters (.0049 and .01 inches). Coarser sand is preferred in hydroponic applications for proper aeration to the root zones and free drainage.
Coarse sand used as a hydroponic media must be screened to eliminate clay particles and/or silt and should freely drain without puddling after irrigation.
Sawdust as a hydroponic growing media was popularized in the coastal areas of British Columbia due to its ready availability, relative light weight, and economical cost. The sawdust used is not the typical fluffy coarse sawdust, but rather one with a generous blending of wood shavings, which provides better moisture consistency throughout the media. Due to advancements in specifically formulated hydroponic growing mediums, sawdust is rarely used in modern hydroponic applications.
Sawdusts generated from Douglas fir and western hemlock trees have been found to provide the most satisfactory results, while the Western red cedar should never be utilized as a hydroponic medium due to its toxicity to plant roots.
Soilless potting mixes generally contain some mix of sphagnum peat moss, sand, perlite, pumice, and/or vermiculite. Different compositions are blended for differing plants and phases of plant growth.
Since there is no plant nutrient value in any of the ingredients, these soilless mixes require a complete hydroponic nutrient solution. Alternatively, dry nutrients are often mixed into the soilless mix, often of a time-release nature to sustain longer term plant growth.
Stonewool or Rockwool
Basalt rocks and chalk make up the raw material for stonewool, otherwise known in horticultural circles as the hydroponic growing media rockwool. This stone is melted in high temperature ovens to 1600 degrees Centigrade. A lava is formed as a result which is then injected into a spinning chamber, which stretches the lava into fibers in a process not dissimilar to that of making cotton candy. These newly formed fibers are then packed together into large mats from which various sized growing slabs, cubes, and blocks are cut. Stonewool products hold large amounts of water while possessing an excellent air to water ratio so that roots don’t rot. Popular for use in drip irrigation and ebb and flow hydroponic applications.
Part of the phyllosilicate group of minerals, horticultural vermiculite has an appearance similar to that of mica. It is mined in various parts of the world, including Brazil, China, South Africa, the United States, and Zimbabwe. Horticultural vermiculite is a hydrated phlogopite mica that expands to many times its original volume when exfoliated, or heated to extremely high temperatures. Vermiculite is primarily used to aid in drainage and as an aeration amendment that also happens to hold a fair amount of moisture and nutrients. As a result of the manufacturing process, vermiculite is long-lasting and sterile. It does not rot, deteriorate, or mold. The pH of vermiculite can vary between 7.0 and 9.5 due to the presence of associated carbonate compounds. Vermiculite has excellent cation exchange properties, is very lightweight and easy to handle. It is more popular as a soil loosening amendment than as a hydroponic growing media.