Every hydroponic gardener has his or her own preferences. There isn't one growing media that is better than the rest. Some of the most widely used growing medias include Coco coir, Rockwool, Lightweight Expanded Clay Pellets (called, Hydro corn or Grow Rock), and Perlite or Vermiculite. While there are a lot of materials that can be used as growing media in hydroponics, they can all have very different properties.
Coco coir is quickly becoming a favorite among hydroponic gardeners. It’s made from ground up coconut husks and represents a giant leap in hydroponic growing media. Coco coir has a great air to water ratio. Best of all, it’s completely renewable. This media is also good for: drip systems, Dutch buckets and auto pots. Not as good for ebb and flow, as it can be washed away.
Perlite has been around for years, mainly for use as a soil additive to increase aeration and draining of the soil. Perlite is a mined material, a form of volcanic glass which when rapidly heated to more than 1600 degrees, it pops much like popcorn as the water vaporizes and makes countless tiny bubbles.
Perlite is one of the best hydroponic growing mediums around. Used by itself or as a mixture with other mediums. Perlite is commonly used with vermiculite (a 50 - 50 mix is a very popular medium), and is also one of the major ingredients of soil-less mixes. Perlite has good wicking action, which makes it a good choice for wick-type hydroponic systems and is relatively inexpensive.
The biggest drawback to perlite is that it doesn't retain water well which means that it will dry out quickly between watering. Worth noting that the dust from perlite is bad for your health so you should wear a dust mask when handling it.
There are many kinds of soil-less mixes containing a vast assortment of ingredients. Most contain things like Sphagnum moss, Perlite and Vermiculite.
These kinds of growing medium are usually considered organic and are frequently used for container gardening wick systems and on-recovery drip systems. They can be used in recovery systems, however most of these mixes have some very fine particles that can clog pumps and drip emitters if you don't use a good filtration system. You can use panty hose as a filter on the return line and on the pump inlet to filter out the fine particles.
Most soil-less mixes retain water well and have great wicking action while still holding a good amount of air, making them a good growing medium for a variety of hydroponic and organic gardens.
LECA (“light expanded clay aggregate”), also known as Clay pebbles or hydroton, is a hydroponic substrate with units about the size of marbles or peanuts. Because they’re so lightweight, easy for transplanting and harvesting, and easy on the hands, they’re a favorite of small producers using media bed or Dutch bucket techniques. Clay pebbles can also be used in both hydroponic and aquaponic systems.
Rinse and soak before use to remove debris and dust from the factory. This will ensure that you eliminate murky problems in your reservoir down the road, and the lesser-known process of soaking the pebbles is crucial to truly maximize yields with expanded clay. Soaking for 6-24 hours, preferably with an air-stone before planting allows water to percolate through the clay’s micro-pores, completely saturating the media. After an adequate soak, you will notice the media is heavier.
In an airy media like expanded clay pebbles, you want to ensure the roots don’t have to travel too far to find water, otherwise, wilting will occur. As a general rule of thumb, make sure a 3-inch radius of pebbles around your plants is always fully saturated.
Add a Small Amount of GRO Nutrients® SUPER GRO organic crop feed and place it in a container after rinsing the media. Ensure that your nutrient solution has an electrical conductivity of no more than 0.4. If you don’t have a ppm/EC meter, use your base grow nutrient at one-quarter strength. You may also choose to boost your nutrients with GRO Nutrients® GRO LUSH hydroponic plant enzymes to ensure a clean transition when you transplant.
Starting seedlings using only expanded clay is doable, but we recommend starting in stonewool, which easily transfers into the clay. If you want to start seedlings in nothing but expanded clay, though, it can be done.
Obtain small starter net pots, which are usually between 1.5 and 2.5 inches in diameter. Fill with pre-soaked clay pebbles. Place seeds on top and cover with one or two loose pebbles, depending on the type of seed being planted. The pots can then be placed in a humidity dome with a spaghetti line affixed to mister fittings.
Crushing clay pebbles using a hammer or something similar breaks up the media into smaller pieces, thereby reducing the size of macro-pores substantially and increasing the media’s water retention capacity, which is ideal during the sensitive germination phase.
Simply place the desired amount of pebbles into a garbage bag or something similar and smash them. In this state, treat the crushed pebbles as a traditional potting mix until you are ready to transplant into the final system. Ensure you don’t crush the medium too finely—you don’t want it to fall out of your net pots.
If you plan to start clones using clay pebbles, there are two methods growers routinely use. There is the low transplant technique—usually used in deep-water culture—and the top drip method. The low transplant technique is simple, you only need to remember two things: provide humidity up top, and plant your node down low in the pot. In other words, only fill your net pot about one-third to one-half full and then plant the stem 1-inch or so below the pebbles.
This allows the portion of the pebbles that are submerged in the deep-water culture reservoir to act as a wick for the couple inches above the water line where the clone has been positioned.
It is hard to claim that any hydroponic medium is 100 per cent inert because most of them have a specific pH value and cation exchange capacity (CEC). When describing a media as inert, most growers are really just referring to its lack of ability to provide any real measureable nutrients, or the ability to take away nutrients from the plant.
This white substance is salt residue left over from the solution. If left to build up for too long, it could eventually lead to phytotoxicity, which chokes out and starves the plant of water or nutrients.
With expanded clay pebbles, watch out for the clay’s high CEC value. Its high CEC value means the clay has the ability to bind with and hold nutrients for longer. Because of this, you might eventually notice an encroaching, whitish substance on top of your pebbles.As a preventative measure, be sure to routinely pull your plants out of the system (if growing in pots) and rinse from the top down using fresh, pH-adjusted water (use pH Up or pH Down products if you need to). If you’re not using pots, simply leach (flush) the entire system using fresh, pH-adjusted water. This will eliminate any toxic salt buildup in the system.
Hydroton is pH neutral, which means that you can rest a little bit easier about finding the proper pH balance. In Aquaponics, you want to make sure that your pH always stays under 6.3 and above 5.6. If they start to head outside of this range, your plant will start to be deprived of certain essential nutrients. Some hydroponic media are either acid or alkaline, which, while certainly manageable, can make having an ideal pH in your hydroponic garden a little more difficult.