Guide to Hydroponic Growing Media

In a hydroponic farm, plants grow in water rather than soil. But without the traditional soil as a growing medium, hydroponic growers have a tough question to answer: which growing media is best for my hydroponic farm? The most common media options are coconut coir, rockwool, peat moss, and perlite. We’ll discuss these and others below.

Coco Coir

Coconut coir, or coco coir, is a byproduct of the coconut harvesting industry made from the rough, brown, fibrous husks of coconuts. You may also see it called coco peat, coco-tek, or ultrapeat. It’s an entirely organic material that is highly inert and holds water exceptionally well. It’s an environmentally friendly product, completely renewable, and can be composted when no longer needed. Many growers use it in a 50/50 ratio with other media like clay pellets or perlite because it may hold too much water if used alone. 

Pros

• Organic

• Eco-friendly and sustainable

• Excellent water-to-air ratio

Cons

• Doesn’t drain well, should be mixed with other media

• Must be replaced after a few uses 

Rockwool

While rockwool might sound like a very stiff and scratchy sweater material, it’s actually a fascinating material for hydroponic growing. The material is created by melting rock down and then spinning it into fibers, similar to fiberglass. These rockwool fibers are then pressed into cubes of different sizes, often used for sprouting hydroponic crops. 

Unfortunately, the medium has some pretty serious drawbacks, even though plants seem to love it. It doesn’t ever break down, so it’s almost impossible to dispose of. It’s also not very environmentally friendly medium to produce. Rockwool cubes often have a very high pH and must be soaked before they’re used. And the dust of the fibers can be an irritant to your eyes and respiratory system. 

Pros

• Retains water well

• Good aeration

Cons

• Dust is an irritant and possibly carcinogenic

• Cannot be disposed of 

• Not environmentally friendly

• High pH, must be soaked before use

Peat Moss

Peat moss has been in use in farming for centuries, primarily for packing plants and for compost. It is a dead fibrous material found in peat bogs, which are typically cool, wet environments. Today, many hydroponic growers use this naturally occurring material as a growing medium. 

Peat moss, sometimes sold as Jiffy Plugs or Grow-Plugs, retains water and plant nutrients well. It commonly offers several years of use from a single plug, so you won’t have to replace it as often as some options. And unlike organic compost, you won’t have to worry about it hiding any weeds or microorganisms. Unfortunately, peat moss is not a renewable resource, taking thousands of years to form, so it’s not the most environmentally responsible option available. 

Pros

• Good water retention

• Holds up for years

• No concern over weeds or microorganisms

Cons

• Not renewable

• Acidic

• Can be expensive

Perlite

Among the most common growing media available, perlite is already familiar to many soil-based farmers and gardeners, who have been using it for years as an aerator for soil mixes. This medium is made from a form of volcanic glass, which occurs naturally and has excellent oxygen retention. It looks like rough white gravel. Perlite is an excellent choice for long-term crops, but be careful. Because it is so light, it can easily be washed away in certain types of hydroponic systems.

Pros

• Lightweight

• Inexpensive

• Aerated

• Can be reused

Cons

• Too lightweight for some systems and may wash away

• Produces dust that should not be inhaled

• Typically obtained by strip mining

Other Growing Media Options

Beyond these four options, there are several other media that are popular among hydroponic growers. Some of these may be slightly harder to find, but if they work well for you they may be well worth the effort.

Clay Pellets

Expanded clay pellets sometimes go by the name LECA which stands for lightweight expanded clay aggregate. They look like small, rounded balls or berries and are both lighter than clay and more porous. These were once the growing medium of choice for hydroponic systems but have largely fallen out of favor because they can tend to be quite heavy in some system types. They also don’t hold water as well as some media, leading to quick dry-out times. 

Gravel

If you wash it well first, you can actually use almost any sort of gravel in some hydroponic systems. Because it’s extremely cheap and readily available, many first-time hydroponic growers use this budget-friendly option. Unfortunately, it doesn’t hold water well, meaning your plant roots may dry out if they’re not watered often enough. It can be cumbersome and isn’t appropriate at all for some types of systems.

Pumice

Pumice is a lot like perlite in that it’s a natural mineral formed as a result of volcanic activity. This lightweight, porous stone holds both water and air well but may be too light for some hydroponic systems. 

Rice Hulls

Like coco coir, rice hulls are a byproduct of agriculture, and therefore a highly sustainable option. These hulls are the shells in which rice grows. The biggest downside of using rice hulls is that they decay after a while, so you have to change them out regularly or risk damaging plant root systems. Since the hulls aren’t sterilized, they also bring a slight risk of introducing microorganisms or weed seeds into your growing environment.

Sand

Sand is cheap (or free, depending on where you are) and plentiful, making it a favorite for low-budget growers. Unfortunately, it offers very little aeration, so it’s a good idea to mix it with another material such as perlite or coco coir. It may also be a bad option for some hydroponic systems as it can erode into narrow waterways and cause blockages.

Sawdust/Wood Chips

Again, sawdust and wood chips are extremely inexpensive or even free if you know a woodworker. They are organic and an eco-friendly option for those looking for green growing techniques. Be sure the wood used wasn’t treated to avoid introducing harmful chemicals to your system. Sawdust can have the problem of clumping and becoming waterlogged, but wood chips don’t have that drawback. 

Vermiculite

Vermiculite is made from hydrated minerals and comes in the form of small pellets. It holds water better than perlite but does not aerate as well, so there is a danger of root suffocation. It can be used to wick water upward, so it’s often a good idea to plant with 50% vermiculite over 50% perlite to get the best features of both materials.

No matter what you prefer to use as a growing medium, hydroponic greenhouses are an exciting and beneficial way to grow commercial crops. Sign up for a virtual tour of an Eden Green Technology greenhouse to see our operations in action, or contact one of our experts to learn more about starting your own vertical farm.