How to Grow Hydroponic Vegetables and Herbs Using vermiculite

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Brock Ingham
Brock Ingham

Vermiculite is a regular fixture on suggested lists of easy-to-use growing mediums. It’s easy to find, relatively cheap, and safe to use. But how does vermiculite compare when stacked against a comprehensive list of growing mediums? What does it bring to the table for the home grower?

Vermiculite in hand
Vermiculite in hand

What is vermiculite?

Vermiculite is an expanded form of mica clay ore. When used as a hydroponic growing medium it has excellent water holding capacity and is a good choice to improve water retention in blended media.

“Vermiculite is a micacious mineral produced by heating to approximately 745°C. The expanded, plate-like particles which are formed have a very high water holding capacity and aid in aeration and drainage. Vermiculite has excellent exchange and buffering capacities as well as the ability to supply potassium and magnesium. Although vermiculite is less durable than sand and perlite, its chemical and physical properties are very desirable for container media.”

Dr. Don Wilkerson, Professor and Extension Specialist Emeritus, Texas AgriLife Extension Service

Vermiculite is an inorganic mineral substrate. It starts life as a form of mica rich clay ore. The mineral is crushed and tumbled into loose fragments, and is then ‘exfoliated’. This process heats the crushed ore inside an industrial furnace to temperatures of up to 2000°F (1100°C). Water trapped between the layers of mineral clay flash boil and fracture the material into light, airy flakes.

The end result is a light, open structured medium with excellent absorbency. I like to think of vermiculite as being a bit like puff pastry. It has lots of inviting, open layers that draw in moisture and nutrients that your crops will find just as delicious.

What are the Benefits of Using Vermiculite?

Vermiculite’s primary trait is its phenomenal ability to hold water. Its structure gives it a very high Water Holding Capacity. Those airy open layers contain many charged particles that pull water deep inside, holding it tight.

That same electrical charge gives vermiculite an excellent Cation Exchange Capacity. To put it simply, a high CEC material tightly holds the mineral salts that provide fertility to your nutrient solution. The vermiculite will hold onto vital nutrients even as the water is used by the plant or drains through. It also comes with a small amount of its own nutrition, mostly in the form of potassium and magnesium.

Vermiculite also serves as a phenomenal pH buffer in your home hydroponic garden. It takes an awful lot to shift it away from its baseline neutral pH. Even scientists studying pH in laboratories have found it so stable that it interferes with results and can tank research into acid damage on plants. It’s just that reliable!

What are the Disadvantages of Using Vermiculite?

Sometimes the high-water holding capacity of vermiculite works against it. It has low air filled porosity – it holds very little oxygen when wet. When saturated it forces all air from the medium and results in a wet, soggy environment that can smother roots. All healthy root systems need lots of little pockets of air around them, and vermiculite will simply fill all available space with water instead.

Vermiculite must also be handled gently. The expanded layers are fragile and if treated roughly can compact entirely and destroy the internal spaces that are so critical to its water holding powers. It’s also prone to throwing up dust during use. In general vermiculite doesn’t contain anything harmful, but it’s still recommended that you wet it during use to reduce inhalation risks.

Another big drawback is that vermiculite can’t be re-used. It’s too fragile for steam treatments and too porous for chemical ones. The same network of cavities that prove so useful at holding water and nutrients also provide a refuge for fungi and bacteria. Once it’s come out of your system there’s no going back, and it needs to be discarded.

Pile of Vermiculite
Pile of Vermiculite

Vermiculite Vs Perlite in Hydroponics: What Are The Differences?

Perlite is very similar to vermiculite in many ways. Both are an expanded mineral. Perlite is made from expanded volcanic stone, super-heated in a similar way to mica until it pops like popcorn. They’re both inert so they won’t rot over time, and they are pH neutral for entire time they’re in your rig.

The most substantial difference in these two substrates comes from differences in their structure. The structural properties of the volcanic stone and mica clays create very different end products even if they’re formed in much the same industrial furnaces.

Volcanic rock has lots of little irregular pockets of trapped moisture that puff the perlite into the fluffy, airy form so well loved by hydroponic growers. Mica on the other hand has a layered structure that results in very regular, flat flakes when heated. That differing final form changes how they interact with water and air.

Perlite holds air wonderfully. While it has very admirable water holding capacity, it still holds lots of oxygen no matter how drenched it becomes. This is fantastic for the roots of your hydroponic plants. It helps prevent fungal issues and allows the root system to thrive.

Vermiculite however holds water far better than it does air. It can contribute to waterlogged crops and even with good flow-through still keeps moisture locked tight against the roots. It also has a higher CEC than perlite and will hold more nutrition.

What Vegetables Can I Grow Using Vermiculite Hydroponics?

Blend it well and you can grow just about anything in vermiculite. It’s a popular choice for commercial growers due to its low cost and excellent CEC.

Vermiculite is also an excellent water retention agent that will help keep your crops well hydrated. It’s particularly useful for plants grown in Ebb and Flow and Dutch Bucket systems, where the water added in small doses needs to last.

This makes vermiculite one of the best materials for thirsty crops, especially when blended with other media. Consider using vermiculite to grow:

Vermiculite is also great for hungry crops. It holds nutrients far better than my other personal favorites of perlite and coco coir. Add it to systems used to grow:

Vermiculite being mixed into soil
Vermiculite being mixed into soil

Can You Grow in Pure Vermiculite?

I don’t recommend pure vermiculite as a hydroponic substrate. It simply doesn’t hold enough oxygen for most plants and can contribute to root problems. Healthy roots need lots of air to prevent fungal diseases like Pythium or Phytophthora setting up camp in your rig. Both those nasties love the damp conditions created by a substrate of pure vermiculite.

Can You Plant in Perlite and Vermiculite Together?

Perlite and vermiculite play to each other’s strengths when mixed together. Perlite holds oxygen, and vermiculite keeps things nice and moist. Add an organic element like coco coir or peat and you’ve got a material that will grow just about anything you can think of.

A blend with one third each perlite, vermiculite and an organic element is an excellent ratio for most crops. Even fussy root vegetables like carrots will do well in this sort of mix.

Final Thoughts

Vermiculite has some astonishing properties that can provide a real boost to your indoor growing, if you know how to use it appropriately. Mix it well with other materials and it’ll provide a steady supply of moisture and nutrients that provides a measurable boost to growth.

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