hydroponic growing media

Hydroponic Growing Media

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By Emily Cooper

While growing plants in a hydroponic system will mean there’s no soil, there’s still a need for growing media. This is for the plants’ roots to grab onto, otherwise, there’s no support for them, and they can topple over.

There’s a vast selection of hydroponic growing media on the market. All of them have their pros and cons and guarantee better growth for the plants they anchor.

But why is it so crucial for hydroponic growers to have growing media in their net pots?

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Why is Your Hydroponic Growing Medium Important?

Your growing medium helps your plant’s roots to store nutrients, oxygen, and moisture when the system isn’t running. As mentioned before, the growing medium also helps to anchor your plants in place.

Without a growing medium in your hydroponic system, the plants would topple over and die.

These growing media are free from soil-borne diseases as well as pests.

Anything can be a great growing medium. For instance in an aeroponic system the plants are anchored by pegs and water vapor delivers the nutrients to the roots. Then again, an aeroponic system is a very different method of horticulture.

So, what exactly makes a hydroponic growing medium great?

What Makes a Great Hydroponic Growing Medium?

As you can imagine, a few criteria need to be met for a hydroponic growing medium to be considered excellent.

These elements include:

Is It Organic?

While some of the growing media on this list won’t be organic, it’s a significant bonus if they are. When a growing medium can biodegrade and is environmentally friendly, it is a major plus.

It also means that your produce won’t be exposed to elements that might make it toxic.

Keeping a Balance

The balance you want to keep is between air and water. When growing in any horticultural field, the mixture of air and water your plant’s roots can access will mean the difference between a healthy grow or not.

Cation-Exchange-Capacity

A cation is a positively charged ion. The cation exchange capacity (CEC) measures how many cations can be retained on a soil particle surface, in soil pH, and even in nutrients.

How your grow medium holds onto its CEC is critical.

Protection

It might come as a surprise, but growing media can protect plants from pH changes in the nutrient solution of the hydroponic system.

This is useful when levels get out of control, which they can do quickly.

Price

Finding a growing medium that is easy to source and inexpensive can make a massive difference to the size of your setup.

Also, a growing medium that is plentiful and available can be an asset when looking to expand operations at a later stage.

Lightweight

Anyone who has carried around bags of potting soil can attest that they are cumbersome. With hydroponics, you don’t want heavy growing media as it can put the system under strain. This is especially true if it is a vertical system.

Also, lugging around soil is a sure way of throwing out your back.

Now that we know what makes a tremendous hydroponic growing medium, let’s investigate the options.

Types of Hydroponic Growing Media

Coco Peat or Coco Coir

There are various names for coco coir, but it’s the brown husk of a coconut shell. For some horticulturists, it is a significant jump in the development of gardening.

To understand why this is a significant jump, we need to understand the natural objective of coconut husks.

Coconut trees grow on the beaches of tropical islands, and when they drop fruit, aka the coconut, they need to be able to survive a journey that can be thousands of miles across salty oceans.

The outer layer of the coconut is fairly soft and rots away. The part that people would most recognise, the husk and hard shell, are there to prevent it from going bad, and from salt and sun damage. And when it does wash up on a beach, it’s the husk that acts as an excellent growing medium in the nutrient-deficient sea sand.

As a growing medium that has naturally developed these natural benefits, coco coir is perfect for hydroponics. It can also deliver significant amounts of hormones while being fungus-free. This means your plants will have the best start in life.

Usually, coco coir is densely packed and needs to be broken apart.

Pros

  • Organic
  • Sustainable
  • Compactable

Cons

  • Can hold too much water

Lightweight Expanded Clay Aggregate (LECA)

In the hydroponic community, LECA pellets are arguably the most popular growing medium to use. LECA is made from expanded clay which is fired in a pottery kiln; these pellets blow up and create their porous texture.

The LECA have no nutrients in them and won’t release any chemicals into the nutrient solution. This also means the pellets won’t affect the pH in the system. And due to their shape and porous texture, the round balls allow for excellent water and oxygen balance.

When appropriately cleaned, these are reusable; otherwise, LECA pellets will retain previous diseases from the last crop.

Compared to other growing mediums, they can be considered a bit bulkier and even a bit heavy when fully saturated.

This being said, it’s nothing compared to lugging around those bags of soil. Another factor to be aware of is the fact that LECA pellets drain very quickly and might leave some plant roots dry.

Pros

  • Reusable
  • pH Neutral
  • Do not clump

Cons

  • Can carry diseases
  • Don’t hold as much water
  • Bulkier than other mediums

Perlite

Usually known for its aeration properties and use to aid in drainage, you can use perlite in your hydroponic system as is.

Perlite is created by putting volcanic glass under intense and rapid heating. The glass then produces tiny bubbles, like popcorn. The result is a porous and lightweight growing medium.

It’s best used in self-wicking systems, but for ebb and flow systems, the water can wash it away. Perlite can hold the most oxygen compared to other growing media in this article. It is also pH neutral.

While you can use it independently, most growers will mix it with other substrates like coco coir. And one issue with perlite is it can form dust that shouldn’t be inhaled. So, exercise caution if using it in your system.

Pros

  • Well priced
  • pH Neutral
  • Lightweight
  • Reusable

Cons

  • Easily washed away
  • Dust can be a health hazard

Vermiculite

Another substrate additive that most gardeners will be well-acquainted with is Vermiculite. It is produced by exposing hydrated laminar minerals to extreme heat. The result is a small, clean, odorless pellet.

It is also nearly pH neutral and is non-toxic and sterile. It can retain water very well but doesn’t provide as good aeration as perlite.

With its ability to retain about 200-300% more water than its own weight, it can suffocate your plants. We’d recommend mixing it with perlite to achieve the best of both worlds.

Pros

  • Great water retention
  • Lightweight

Cons

  • Poor drainage
  • Can suffocate plants

Hemp Fiber

Hemp fiber is excellent as a hydroponic substrate as it has a neutral pH and biodegradable properties. It can also retain water and nutrients well. These properties make it a great candidate for germinating seeds, and its porous nature allows for solid root growth.

It’s not the lightest growing medium, and sometimes it can retain too much water. But if you are growing microgreens, hemp fiber is perfect. And depending on where you source it from, it is organic and sustainable.

Pros

  • Great water retention
  • Biodegradable

Cons

  • Poor drainage

Rockwool

As a substrate, Rockwool has been around for years. It is produced by melting rocks and spinning the molten substance into long thin fibers. These fibers could be compared to fiberglass, but rock.

Rockwool has been a favorite of the hydroponic growing community. But this being said, there are several downsides to using it. Namely, it is not biodegradable and is hard to dispose of. It also has a high pH and needs to be soaked before being used.

It also releases dust which can be harmful to inhale.

Pros

  • Great water retention
  • Easy to use

Cons

  • Can be harmful
  • High pH levels

Phenolic Foam / Oasis Horticube Growing Medium

This substrate is the green substance that’s usually used to hold flowers. It is relatively rigid and can retain water and nutrients while allowing for good aeration. It’s very similar to Rockwool cubes, except cheaper.

But it is also not biodegradable and not natural.

Pros

  • Cheaper
  • pH Neutral
  • No presoaking require

Cons

  • Not biodegradable
  • Beneficial for germination but not useful for the full grow cycle

Starter Plugs

As the name would indicate, starter plugs are used for either propagating plants or seed germination. They are made from organic materials, including coco coir.

Their environmental credentials make them a popular choice for hydroponic gardeners. Starter plugs are great at retaining moisture while not becoming waterlogged. Some of them will come with nutrients embedded into them, but this does vary from brand to brand.

They also expand and allow the roots to dig into the substrate. This being said, they are only used for propagating and germination.

Pros

  • Excellent for seedlings and propagation
  • Sustainable (depending on the material used)

Cons

  • Only suitable for seed starting or cloning.
  • Relatively expensive

Growstones

Produced from discarded glass bottles heading to the landfill, growstones are crushed into a powder and mixed with calcium carbonate. The mixture bubbles and then when it cools the result is similar to lava rocks.

They are lightweight, sustainable, very porous, and allow for excellent aeration. Growstones are also pH neutral and retain moisture well. Before using, make sure to wash off the small particles and dust.

You can use it on its own or with other growing mediums.

Pros

  • Lightweight
  • Good air to water ratio
  • Sustainable

Cons

  • Can cling to some roots causing damage
  • A little bit of dust
  • More expensive than other media

Pumice

While this is a mined material and usually associated with foot care, pumice is excellent for hydroponic use.

Formed by super-heated and pressured volcanoes, it comes in various colors. They are also porous, slow to break down, hold onto water, and retain oxygen well.

However they float, which can be problematic for some hydroponic systems like deep water cultures.

Pros

  • Lightweight
  • Excellent air holding capacity

Cons

  • Too lightweight for some hydroponic systems

Peat Moss

Another substrate gardeners will be similar with is peat most. It is excellent at retaining moisture and nutrients. As a dead fibrous material it takes years to develop from sphagnum moss. This means while it is organic, it’s not sustainable.

You’d most likely use this in combination with other mediums like perlite, vermiculite, or styrofoam. It will also require some pH adjustments.

Pros

  • Good water and nutrient holding.
  • Doesn’t compact
  • Doesn’t comprise of harmful bacteria or weeds

Cons

  • Not renewable
  • Low pH, acidic
  • Relatively expensive

Brick Shards

As the name suggests, these are crushed-up bricks. Due to dust, they will require some cleaning, and they are not pH neutral. But they are sustainable and cheap to purchase.

These are very similar to general gravel.

Pros

  • Inexpensive
  • Easy to clean
  • Drains well

Cons

  • May affect pH
  • Requires more thorough cleaning
  • Heavy
  • Plant roots may dry out

Gravel

Used in the earlier days of hydroponic gardening, gravel was most prevalent in ebb and flow systems.

It is hard-wearing and allows for ample space between the pebbles. Gravel doesn’t retain water or air but it is reusable and durable. This is a cheap growing medium, although it is heavy.

Pros

  • Cheap (or free)

Cons

  • Poor water retention, not suitable for heavy plant roots
  • Heavy

Rice Hulls

These are the shells that surround rice. Their natural properties mean they are great for drainage but retain little to no water.

But it’s always great to find another use for a byproduct that would typically be tossed away.

They do, however, tend to decay over time.

Pros

  • It makes use of a byproduct that would otherwise be wasted
  • Retains little water

Cons

  • Decays over time

Wood Fiber or Sawdust

This is simply wood. And depending on the wood you choose, it can be sustainable and organic. Select wood that hasn’t been treated, as the chemicals can infuse into the system.

Some wood chips will have some plant growth regulators, which will help boost your plants growth. Wood fiber and sawdust will retain water, but they can become waterlogged.

Also, they can have pests and will eventually biodegrade. You will have to test the pH of the water regularly.

Pros

  • Organic
  • Holds structure for a long time

Cons

  • Biodegradable
  • May not be sterile
  • May attract pests

Sand

Yes, one of the world’s more plentiful growing media. It is cheap and readily available. You must ensure it is sterilized before use and be warned, it has poor water retention. Not to mention it is heavy.

Pros

  • Cheap
  • Easy to find

Cons

  • Heavy
  • Low water retention
  • Small size may affect specific hydroponic systems

Polystyrene Packing Peanuts

Here’s a use for those extra packing peanuts you were wondering how to get rid of. For those keen to use them, make sure to use them indoors as they are incredibly lightweight and will blow away.

They can also leach styrene into the system…

Pros

  • Cheap (often free)
  • Very lightweight
  • Drain well

Cons

  • Only polystyrene will work – biodegradable packing media will turn to slush
  • Potential for plants to absorb styrene