There are many types of growing media that have been successfully used for hydroponics and there are probably many more that have never been tried.
1. Perlite – a volcanic rock a gray obsidian, that has been heated to 1500 degrees F in a kiln and expanded. It is a light weight porous material that can “wick” water from a bottom container of water.
2. Ceramic grow rock – a clay material also called Geolite, which is often used for aquaculture because the porous material is a good media for growing bacteria to clean water. It does not break down.
3. Rockwool – a material made from rock spun into a fiber like material. A phenol based resin is added as a binder. Rockwool also tends to increase the pH of the water.
4. Pea gravel – this media is just simple gravel but has been graded for size and shape. It is not a porous media so it does not wick water from below and must be used in a system that provides aeration for the water. It can be used to grow bacteria as well as plants.
There are many other types of media used in hydroponic systems. Some have special advantages and disadvantages.
Sand – Many sands, such as beach sand, have salts already in the media, that can cause problems in hydroponics. However, sand is a useful media that retains water. It has to be sterilized between crops.
Sawdust – where there is an extensive timber production, sawdust may be available. The species of tree is important, with softwoods decaying more slowly than hardwoods. Douglas fir and western hemlock work great but red cedar is toxic to plants. Some sawdust is from logs soaked in salt water and is therefore toxic to plants.
Peat – There are three types of peat: peat moss, reed sedge and peat humus. Peat is very acid and can lower the pH of the nutrient water. It breaks down after one or two growing seasons.
Vermiculite – This is a volcanic mica which has been popped in a kiln. It is a magnesium aluminum iron silicon material that can be compressed and lose its porosity.
Pumice – A silicon material of volcanic origin can break down after repeated use.
No media – There are many hydroponic systems that use no media whatsoever. The plant is usually started in a small piece of rockwool, or specially designed plastic collar. The plant is then placed in a growing tube or container that applies nutrient water to the roots.
by Professor Hydro
There are probably hundreds of different kinds of growing medium, anything that a plant can grow in is considered a growing medium. There are manmade as well as organic (natural) mediums. Even plain old AIR can be an effective growing environment for roots.
I have been asked many times what growing medium is the best. This is like asking what is the best color? Or what is the best kind of vehicle to own. Sometimes the answer depends on the job you need it to do. You wouldn’t try to use a soiless mix in an Aeroponic system and you don’t plow a field with a Rolls Royce limousine. However, if you want to build a Non-Recovery Drip hydroponic system then the soiless mix would be an excellent choice, and a John Deere tractor can handle the field (save the Rolls for a night on the town, pick me up at 8). What I’m trying to say, is that the best growing medium for your purpose depends on many variables. The type of system you are using, what kind of crop you are growing and local environment are just some of the many determining factors involved when choosing a growing medium. There may be several mediums that will work equally well for your particular needs. Many times it boils down to availability, price or personal preference.
I have listed the most popular types of growing mediums, read below to view details about their general use, advantages and disadvantages, and particular characteristics of the specified growing medium.
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|The Hanging Gardens of Babylon were thought to be sand-based hydroponic systems (what else would you use if you’re stuck in the middle of the desert?). This is probably the first hydroponic growing medium ever used, and it is still being used successfully.
Sand has a tendency to pack tightly together reducing the amount of air available to the roots. So you should use a coarse builders sand or mix the sand with perlite or other material that will increase aeration.
|I have never personally used fiberglass insulation but I have known several people that have used it in their hydroponic systems. There were mixed reviews, and none of those people are still using it.
The most common complaint that I have heard is that it retains too much water, not leaving room for enough air around the roots, which can cause problems with the plant. I have heard that sometimes the insulation is treated with chemicals for fireproofing, etc., so unless you want to experiment, the Professor would not recommend using fiberglass insulation.
People talk about hydroponic systems that do not use any growing medium at all. As far as I know, that would be impossible. The plants roots would have to growing in a complete vacuum. This would instantly kill the plant.
Air on the other hand is frequently used as a growing medium. Aeroponic systems have the plants roots hanging in air and are periodically sprayed with a nutrient solution.
The biggest advantage to growing in air is the roots get all the oxygen they could possibly need (roots need plenty of oxygen). Another major advantage to air is it’s cost (Free is hard to beat!). There is no disposal problems as with some other mediums either.
The biggest problem associated with aeroponics is it’s susceptibility to power failures and pump or timer failures. There is NO buffer.The roots could start to dry out within minutes and the loss of the total crop can come very quickly.
|This growing medium has been used for years and works well. Many or the earlier hydroponic systems that were commercially available to the public were gravel based ebb / flow (flood and drain) type systems.
Gravel supplies plenty of air to the roots, but doesn’t retain water, which means that the plants roots can dry out quickly if they are not watered enough. Another drawback to gravel is its weight, it’s very heavy, and toting it around is difficult.
Gravel is usually fairly cheap (depending on where you live) and easy to find. You can easily reuse gravel as long as you wash and sterilize well between crops. After you harvest your crop you can wash the gravel to remove all the old roots and then sterilize them with a 10% bleach and water mix (one part bleach to 9 parts water). The gravel can also be sterilized by using a mixture of Hydrogen Peroxide and water (use 1 or 2 teaspoons of 35% food grade hydrogen peroxide per gallon of water).
|This growing medium has had limited success. There are many variables that determine how well saw dust will work, most predominantly is the KIND of wood that the dust is made from. Some kinds of wood can give off chemicals that are detrimental to the health of the plant(s). Another problem with saw dust is that it will decompose, which can cause problems. Saw dust also retains a lot of moisture so care must be taken not to over water.
The best thing about saw dust is that it’s usually free. I don’t recommend using saw dust unless you are into experimenting.
Choosing a Media
The hydroponic plant roots need to have both nutrient water and air.
If the water is pumped or poured only once or a few times a day, there should be enough media around the plant roots to capture and retain some water. This means the media should be somehow able to capture some air and some water. That is why the “best” hydroponic media are porous materials like pumice, perlite, grow rock and rockwool.
Also, in a system that is pumped or pored a few times a day, there should be some reservoir of extra water for the plant. If the plant runs out of water, first it shuts down or quits working, and then it starts to die.
If the plant roots have a growing area, with both water and air, and a water reservoir, the plant will continue to thrive and grow. If there is a small plant root growing area, or the plant roots run out of water, the plant does not thrive.
If the plant roots “see” extra water below the root growing area, the plant does not have to grow extra root to “find or follow” the water. So the plant can relax about its water supply and use its energy to grow more above ground.
In the simple tub system, there is a root growing area, the water reservoir, and the overflow water container. There is a way to design this to help the plant grow.
The plant root growing area is the area where the roots see air and water. How much area is needed for the plant partly depends on the type of media, how it holds both air and water.
Perlite is an excellent media because it “wicks” water, or draws up water from below. The best mixes of water and sir are in the 50-60% range, and with perlite this area can be up to about 4 inches above the water level.
If a media like perlite is used, less area is required for the root growing area.
Comparing Growing Media
Many types of growing media have been used for hydroponics and there may be many more that have never been tried. Some of the common types of media that are used in hydroponics are:
Rockwool – a material made from rock spun into a fiber like material. A phenol-based resin is added as a binder. Rockwool also tends to increase the pH of the water.
Pea gravel – this media is just simple gravel but has been graded for size and shape. It is not a porous media so it does not wick water from below and must be used in a system that provides aeration for the water. It can be used to grow bacteria as well as plants.
Different media provide different positive and negative affects for a hydroponic system. Also, some are more available or cheaper than others are Some have an environmental impact greater than others do, in the ways they are gathered or manufactured.
If you can find perlite, it is probably the best media you can use for a home system. Perlite is forgiving for the beginner because it will retain water for three or four days if you forget to water your system. If Perlite is not available, gravel is a good second choice because it will allow for a once a day watering and does not break down.
In this experiment you can compare plant growth behavior in 4 types of growing media.
1. Prepare four growing pots in a water container.
2. Fill each with a different media such as gravel, perlite, sand, etc.
3. Plant a bean or pea seed about 1 inch below the surface of the media in each of the four pots.
4. Place the pots sunlight or sufficient artificial light and record signs of growth for each media every day.
DATA RECORD SHEET
Inspect, observe and record data about the plant’s condition. Once the plant has germinated and broken through the growing media, include an illustration of its appearance and begin recording on Day 1.
Buckets, Nets, Baskets.
Metering and Measurement