Types of Hydroponic Substrate
In most hydroponic gardens, soil less growing mediums are used primarily for starting seeds and when rooting cuttings. The less medium a system requires, the easier and less expensive it is to operate. This is a major consideration for those intending to make a profit from their hydroponic gardens. Modern day soilless mediums have come a long way since the use of river gravel and sand in early systems. A perfect medium is able to hold a nearly equal concentration of air and water. As you have learned, your plants need both oxygen and nutrients to reach their roots. The water/air holding capacity of a growing medium is determined by the small spaces between each granule or fiber. These “holes” in the medium are known as “interstitial spaces.”
Fine sand features very small interstitial spaces that cannot hold much air and water. On the other hand, coarse gravel has large interstitial spaces that can hold a lot of both air and water. Yet, as science would have it, once the interstitial space gets to be too large for capillary action to hold the water in place, you guessed it, the water runs right through it. If your system constantly re- circulates your nutrient solution, a fast draining medium would be acceptable. But obviously, coarse gravel isn’t a good medium for a system that doesn’t constantly circulate nutrient to the plants.
Types of Hydroponic Substrate
Coconut Coir
My favorite loose growing medium is coconut coir, otherwise known by trade names like Ultrapeat, Cocopeat and Coco-tek. Coco coir represents a major step forward in organic soilfree growing mediums. It combines the water retention of vermiculite with the air retention of perlite, however it is a completely organic medium made from shredded coconut husks. Why coconut husks? The coconut husk serves its seed two purposes: (1) protection from sun and salt while floating in the ocean; (2) a hormone-rich and fungus free medium to speed germination and rooting upon landfall. Finely shredded and steam sterilized, coconut coir offers plants an ideal rooting medium that also offers protection against root diseases and fungus. And unlike peat moss, which is rapidly becoming depleted from overuse, coir is a completely renewable resource. You can now find several variations of coir on the market. The most popular is the compressed briquette format, which requires soaking in a gallon of water before use. During soaking, the coir re-hydrates, expanding up to six times the size of the original briquette, resulting in about 1/3 cu. ft. of loose coir with a consistency and color that most closely resembles fresh ground coffee. As an added benefit, coir doesn’t soil your hands, clothes, or carpets. It brushes off readily, without any residue.
Perlite
Perlite has been around longer than any other soilfree growing medium. Made from air-puffed glass pellets, and nearly as light as air, perlite has excellent oxygen retention. Its ability to retain oxygen is the main reason it is used as a supplement in soil and soilfree mixes. The main drawback of perlite is its lightweight consistency, which makes it easy to get washed away. This drawback makes perlite an inappropriate medium in flood and flush type hydroponic systems or those that would be subjected to strong wind and rains if situated outdoors.
LECA /Clay Pebbles
LECA stands for Lightweight Expanded Clay Aggregate and is an extremely coarse growing medium. Some of its common trade names include Geolite, Grorox and Hydroton. LECA is made of expanded clay pellets that hold water by virtue of its porosity and surface area. These mediums are pH neutral and reusable, making them ideal for hydroponic systems. While lava rocks appear to have some of the same qualities, they should never he used in hydroponic systems because they alter the pH and leave behind a heavy sediment that can harm equipment. For the same reason, you should always rinse new LECA stones to remove the dust caused by movement during shipment.
Perfect Starts
The latest breakthrough in growing mediums is the “molded” starter sponge made from organic compost and a flexible. biodegradable polymer binder. Available in several shapes and sizes, these innovative growing sponges solve the main problem growers face when wanting to use an organic medium in a hydroponic system. Namely, they do not fall apart or crumble during transplanting which serves to prevent damage to delicate roots. This is a significant advantage, because root damage that occurs during transplant is the leading cause of transplant shock. The starting sponges exhibit a perfect air to water holding ratio, and when used in conjunction with their plastic tray inserts, will guide roots to grow directly downward instead of spiraling, as is the case in many other types of starting trays. Since the plugs don’t crumble, or break apart and clog delicate sprayers, Perfect Starts perform well in all types of hydroponic systems.
Rockwool
Rockwool is made from molten rock that is spun into long, glass-like fibers. These fibers are then compressed into bricks and. cubes, or sold loose as “flock.” Rockwool has long been used to insulate buildings as an alternative to fiberglass, and has been a mainstay in commercial hydroponics for the last twenty years. It readily absorbs water and has decent drainage properties, which is why it is used widely as a starting medium for seeds and a rooting medium for cuttings. In my opinion, the premiere benefit of rockwool is its sterility from pathogens and just about anything else that could contaminate a hydroponic system. Some of the world’s largest hydroponic greenhouses use rockwool slabs to raise numerous varieties of plants to full maturity, and they often reuse the rockwool slabs many times by steam sterilizing the slabs between crops.
Source : how to Hydroponics 4th edition
