Hydroponic Growing Medium – A Guide

What is Hydroponic Growing Medium?

Hydroponics method of growing plants
Clay pebbles work in a variety of systems

Growing medium, or grow media as the plural is called, is a critical component of most hydroponic systems. Growing media helps to stabilize roots and keep plants in place, but it also holds nutrient solution, and helps roots get oxygen. Not every system uses hydroponic growing medium, but many do.

In hydroponics, a system that uses media to retain water and nutrients, as well as stabilize plants, is called a media based system. Media based systems are one of the most common forms of hydroponics, and you’ll see that the majority of setups within hydroponics use some type of substrate.

What kinds of grow media are there?

Hydroponic grow media comes in a variety of forms. Rockwool, coco coir, and clay aggregate (lightweight expanded clay pebbles) are some of the most popular and commonly used growing media. However, other grow media like perlite, vermiculite, rocks, lava rocks, oasis cubes, and parboiled rice husks are also used.

Each growing medium comes with its own set of advantages and disadvantages. And while there’s no perfect, one size fits all grow medium, you can choose the right medium if you know what to look for.

Hydroponic Grow Medium: Most Widely Used Types

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What to look for while choosing a hydroponic growing medium

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Alternative Growing Medium

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Using Rockwool for Hydroponics

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Frequently Asked Questions

Does it matter if I use fast draining or slow draining grow media?

Well, it really depends on the system you’re using. For example, ebb and flow systems do need some moisture retention, but they need good drainage too. For wick and drip systems, a slow draining medium is ideal, since you’re putting less moisture in to begin with. An NFT hydroponics system does well with a medium that allows a little moisture retention, but also drains well. Check out this guide on timing ebb and flow cycles for more information.

Can I mix my own hydroponic growing medium?

You can’t always ‘create’ your own growing medium. But you can mix two different kinds of growing media to get the results you need. Clay aggregate (pebbles) mix well with other media, as do coco coir, perlite, and vermiculite. If you’re mixing a lightweight medium with a heavier medium, use a 50/50 mix (i.e. half of each, like half coco coir and half perlite or clay pebbles). However, some grow media, like rockwool or oasis cubes, are designed to be a standalone medium. They provide the perfect balance of water and air without needing to add anything else. If you’re not sure what combination you need for your hydroponics setup, try to mix fast and slow draining media.

Can I reuse organic growing medium in hydroponics?

You may be able to reuse organic growing media- to a certain point. It really depends on how quickly the medium in question ‘breaks down’ or begins to decompose. Of course, depending on the volume of water going through your hydroponics setup, it can last longer too. Coco coir is a good example of an organic growing medium that can be reused several times. However, rice hulls and, especially saw dust, tend to break down more quickly. You’ll have to replace those more frequently, and likely with every new crop to ensure no pathogens or rotting medium is transferred.

Are perlite and vermiculite the same?

Perlite and vermiculite aren’t the same, although they are similar types of growing media. They both hold water very well and allow a good amount of aeration. Often, you’ll even see them mixed together in media mixes for hydroponics and starting plants. However, they have a few different properties. Yes, they’re both made of highly heated and processed minerals, but the root material is different. They both react similarly when placed in water, but vermiculite has a longer usable lifetime. It’s important to remember that both types of growing media will float when placed in water, and should be mixed with a heavier, faster draining hydroponic grow media.