Soil Free Growing Mediums
Beneficial Soil Microbes That Jumpstart Organic Gardens
Modern day soilfree mediums have come a long way since the use of river gravel and sand. Man made mediums crafted from natural and organic raw materials provide plants with nearly perfect environments for taking root and growing quickly. A perfect medium is able to hold a nearly equal concentration of air and water. As we learned in FG's Think Like Plant feature article about roots, your plants need both oxygen and nutrients to reach their roots. The determining factor in water/air holding capacity of a medium are the small spaces between each granule or fiber. The name for these "holes" in the medium is "interstitial spaces."
Fine sand features very small interstitial spaces which cannot hold much air and water. On the other hand, coarse gravel has large interstitial spaces which can hold lots of both. The next factor we must concern ourselves with is that water has weight and always seeks the lowest ground. In the case of coarse gravel, this means that water will run right through leaving behind only a moist trace. If you constantly recirculate your nutrient solution, this medium would be o.k., if you do not plan to irrigate as freqeuntly, a mixture of Ultrapeat and Aerolite works very well for most container grown plants. Be sure to feed plants grown in inert media with a complete hydropoic nutrient such as the Above & Beyond Nutrient System.
FG Growing Media Selector Chart
Our favorite growing medium is Coconut Fiber or Cocopeat. It represents a major step forward in organic soilfree potting mediums. It has the water retention of vermiculite and the air retention of perlite, however, it is a completely organic medium made from ground up coconut husks! (See our feature on roots)
Why coconut husks? The coconut husk serves its seed two purposes; 1. Protection from the sun and salt while floating around the oceans and 2. A hormone rich, fungus free medium to solicit germination and rooting upon landfall. Ground up and sterilized, Cocopeat offers plants the perfect rooting medium and protection against root diseases and fungus infestation. Cocopeat is a completely renewable resource, unlike peat moss which is rapidly becoming depleted from overuse.
Made from expanded volcanic glass, Aerolite is an extremely lightweight growing media which may be used for seeding, rooting and mixing with other media or alone in bags or for "sack" culture. Aerolite, which is super coarse agricultural Perlite, exhbits an excellent air to water holding ratio. A 50/50 mix of Aerolite and Ultrapeat is great for repotting houseplants as well as starting seeds or rooting cuttings.
A relatively new development in coarse mediums is Grorox, which is product made up of expanded clay pellets that maintain water by virtue of their porous, irregular shape. Grorox are pH neutral and reusable, making them the ideal medium for soilfree gardens and hydroponic systems.
Perfect Starts are made from composted wood bark that is ground and mixed with the biodegradable resin from the rubber plant. In doing so, the Perfect Starts take on the absorbency and resiliency of a sponge, making them an ideal rooting environment for seeds and cuttings alike. Perfect Starts will not fall apart in your hydroponic system like other organic starter plugs. They are meant to be transplanted along with your seedling or cutting into your hydroponic or aeroponic system for the plants to reach full maturity.
Rockwool (Grow Cubes):
Rockwool is made from molten rock which is spun into long, glass-like fibers. These fibers are available compressed into bricks and cubes or as loose material called flock. Rockwool has a good water to air capacity and is widely used as a starting medium for seeds and a rooting medium for cuttings. Some of the world's largest hydroponic greenhouses use Rockwool slabs to raise all sorts of fully mature plants. There are disposal issues and other growing environment stability issues that should be taken into account when using Rockwool.