A hydroponic system is a way of growing plants in a nutrient-rich solution, without the use of soil. But how do you support the weight of the plants without soil? For that, you’d need a hydroponic medium.
In this article, we’ve listed some of the hydroponic grow mediums available, as well as some advice on how to choose.
The Best Hydroponic Medium
The ideal hydroponic medium is inert; which means it doesn’t decay or break down quickly, and thus won’t be absorbed by the plant. It should also hold and drain a good amount of water, allow the roots access to nutrients and oxygen, and have a balanced pH.
There isn’t one medium that is necessarily better than the others. It mainly depends on what you’re trying to grow, what system do you have set up, and what materials are more available in your area
Brick shards are the smashed bits of red building bricks. Growers sometimes use them as a hydroponic medium, but they aren’t ideal because they aren’t pH balanced.
Like many other rock-like materials on this list, you’ll find that they’re good at draining excess water.
Coconut shells are organic and environmentally-friendly.
They are usually considered a waste product, but they actually make a great growing medium.
Although organic, it decomposes very slowly and the plants aren’t likely to absorb any nutrients from it. You generally don’t want the hydroponic medium to interfere with the plant’s nutrition.
Coconut shells are processed into chips or fibers, both of which work as hydroponic mediums, and are sold in bricks for easy handling. The chips have a larger particle size, allowing for better ventilation. It really depends on what your plants need.
Coconut is a good absorbent of moisture. The fiber/chips you buy may expand up to 6 times in size when exposed to water.
The Floral foam has a similar texture to oasis cubes and Rockwool. It has very large pores and absorbs a lot of water. For that, it shouldn’t be in constant contact with the water source.
It can also crumble easily, leaving debris in the water. It’s a difficult medium to work with.
A type of small rocks, the same you may find in an aquarium.
It is cheap, easy to clean, and drains well. It’s similar to river rocks but is smaller in size.
WIthout some other medium to retain water, gravel alone is likely to dry out your plants.
Another problem with gravel is that it may cause pH swings if it stays in contact with water for too long.
A popular growing medium commonly referred to as hydroton. It’s a type of clay that received extra heat to create a porous texture. They are a non-biodegradable, sterile, pH-balanced medium that also happens to be reusable.
However, cleaning and sterilizing large amounts for reuse can be difficult and time-consuming.
Growstone Hydroponic Substrate
Growstones are made from recycled glass, but they don’t have any sharp edges so there’s no risk of getting a cut from them. They are relatively light, porous, and reusable. They have a great wicking ability, almost too great. It’s a good idea to place them deep enough and to have good drainage.
If the wicking causes the uppermost part of your plant to always be moist, it means that the roots may rot. Mediums that have a good wicking ability may be better for taller plants.
Expanded Clay Pellet
These clay pellets are versatile and easy to use. You can clean and reuse them. They’re a bit costly, but may save money in the long run if you reuse them
Their large spherical shape offers good drainage and ventilation, while their porous texture absorbs water.
They tend to drain more than they absorb, so they can dry out plants quickly. They’re also quite heavy.
If you want to keep more water in the system, simply use a more absorbing medium on top of them.
Great for both cloning and germination, these cubes have great water retention and a neutral pH. It doesn’t need any additional treatment.
Oasis cubes are an open cell material, which means they can absorb water and air. They allow the roots to grow freely and they aren’t as prone to waterlogging as Rockwool.
Perlite is a powdery form of obsidian, a volcanic glass. It is processed with heat to create a porous structure.
It is very lightweight and has a neutral pH. It’s mainly used for water retention, but it’s porous enough to allow drainage as well.
If you’re using a flood and drain hydroponic system, lightweight mediums such as perlite shouldn’t be used. They will sway with the water and not support the roots well.
Incidentally, perlite is also used as an additive to cement.
It’s important not to get any of the powder in your eyes or mouth, and to wash them thoroughly if it does happen. You can dampen the material a bit while working to prevent the powder from filling the air. The powder is a nuisance, but it isn’t dangerous.
Pine Bark Shavings
Pine shavings are a good, inexpensive hydroponic medium. When buying them, make sure that they aren’t mixed with sawdust (which can get clogged easily). Additionally, make sure that they don’t have any chemicals or additives, particularly fungicides.
Pine shavings are often sold commercially as bedding for various pets, such as hamsters.
Pine bark is better than most wooden mediums. It’s slower to decompose, and is less likely to interfere with the plants’ nutrition.
Like any type of wood, pine shavings require a good draining system as they tend to soak up water.
A mineral-based medium that is similar to perlite. It is lightweight and has excellent oxygen retention rates.
The lightness makes it unsuitable for flooded systems, especially when bought in a small-particle size.
Rice hulls are a common by-product of rice production. Like coconut shells, they are organic, yet long-lasting.
Rice hulls are sold in many varieties. They can be fresh, aged, composted, and parboiled. Fresh rice hulls can be full of contaminants and should be avoided. Parboiling is the best way to produce clean and sterile hulls.
River rock is very common and inexpensive. It can be natural or artificial. It has round smooth edges that allow water to seep through.
River rocks are not porous, and therefore can’t absorb water. They don’t make a good hydroponic medium by themselves. Instead, it’s best to use them as a draining method, below another medium.
River rocks will keep any extra water away from your plants, which prevents root rot. If you collect the river rocks yourself, make sure to sterilize them.
Rockwool is a common granite or limestone material. It has been heated, melted, spun like cotton candy, and shaped into cubes. This process gives it a porous, cotton-like structure. It’s important not to squeeze the cubes as this will destroy the pores.
Rockwool’s porous structure allows it to hold a lot of water. Make sure your system has good drainage and ventilation, or else the roots may drown or rot. Waterlogging may also be a problem.
Rockwool has a high pH, which is bad for your plants.To balance it, soak the cubes in pH-balanced water before use.
This is a good material for new plants and germination. However, it’s not environmentally-friendly.
Sand is a widely-available hydroponic medium. It works just like any rock, but it has a smaller particle size. The smaller the particles, the more water it retains.
Look for sand with larger particle size, as it provides better ventilation.
Wet sand can get very heavy, so mixing it with other mediums can reduce the load. We recommend coco fibers or Perlite.
Starter plugs are made from many materials. They have a cylindrical shape with a hole in the middle, which helps the roots grow downwards. This reduces branching and makes moving the plant easier.
A silicate mineral that has similar properties to perlite. A rare advantage of it is that it can hold nutrients for later use, just like soil.
Like perlite, vermiculite also floats in a flood and drainage system, making the roots unstable. Other systems may be more suitable.
Simple wood shavings are a great organic medium. They’re good at retaining water and may encourage plant growth. They also support the root structure for a long time.
Unfortunately, wood is not very sterile and may end up attracting pests.
Hydroponic systems have many advantages. They save water, increase yield, and help plants grow faster. They also avoid many problems that plague traditional soil.
Choosing the best hydroponic mediums for your system is an important step to control the flow of water and nutrients.