Best & Worst Substitute of Vermiculite

Most gardeners are familiar with vermiculite as a growing medium. It has been used to replace a variety of mediums, but which is the best? Some may believe that it can play the roles of all mediums, but this is not the case based on my experience.

Generally, vermiculite can be used as a replacement for horticultural grit, sand, pumice, coco coir, and biochar. This is because all of these growing mediums possess excellent water-holding and aeration capacities. By contrast, vermiculite will be the worst replacement for hydroton and gravel.

Which growing mediums are not replaceable with vermiculite? This may be intriguing, so I will be giving their initials (one starts with ‘H’, and the other starts with ‘G’). You will know them better later!

5 Best Growing Mediums to Substitute With Vermiculite

Vermiculite can be used as an efficient substitute for horticultural grit, sand, perlite, pumice, coco coir, and biochar. They can be used interchangeably because vermiculite also possesses similar characteristics to these ideal growing mediums such as water retention capacity and drainage.

If you are looking for substitutes for the abovementioned growing mediums, vermiculite might be one of the best options for you!

Why?

This is because vermiculite has the following ideal attributes:

1. Water Retention. Vermiculite efficiently holds water, providing water to the roots for a longer time.
2. Improves Drainage. Medium to extra coarse vermiculite allows for more air and water spaces in the soil when used as a soil amendment.

In the next sections, I will discuss vermiculite and its similarities with each growing medium. What are you waiting for? Let us go!

1. Horticultural Grit

Horticultural grit is made of inorganic minerals and rocks such as limestone, silica, and quartz. Vermiculite, on the other hand, is formed from volcanic rocks. Both growing mediums can reduce soil compaction and improve soil structure, particularly drainage.

Vermiculite and horticultural grit are similar in a lot of aspects, namely:

1. They are both produced from rocks.
2. They almost have the same texture.
3. They both improve soil structure by providing more spaces.
4. They both retain water.
5. They have eye-catching appearances (different shades of brown & sheen).

These similarities make them applicable in almost the same uses—both are fit as a soil amendment and topdressing.

2. Sand

Medium to coarse vermiculite is an effective and superior substitute for sand. Sand, like vermiculite, improves drainage, making these two growing mediums interchangeable.

Vermiculite can also be used as a replacement for sand if you are looking for a shiny appearance, especially for your ornamental plants!

Sand is used as a growing medium for some ornamental plants due to its heavy weight. However, it lacks the aesthetic element. Thus, vermiculite is an even better alternative because it adds color to your garden.

Fun Fact: Among all the growing mediums in this article, sand is the cheapest option! This is because it is available in most places such as the beach. Sometimes you can even get it for free!

The best way to use vermiculite is to combine it with other growing mediums like potting soil in a 1:3 vermiculite to soil ratio.

   Know more about vermiculite in our article on what is vermiculite. 

HOW TO USE VERMICULITE 101. A SOIL SCIENTISTS THOUGHTS ON THE PROS/CONS | Gardening in Canada 👩‍🔬

3. Pumice

Both pumice and vermiculite are products from the volcanoes and they are comparable in terms of particle size, water retention, and soil aeration capacity. Their likelihood in these certain aspects makes them interchangeable in the gardening context.

Both pumice and vermiculite have particle sizes ranging from very fine (<1 mm) to coarse (4–8 mm).

This allows them to be used in a variety of gardening applications such as:

• Seed starters
• Root cutting starters
• Soil amendment

4. Coco coir

Vermiculite can be used in place of coco coir because it improves soil structure while also increasing water drainage. The only difference is that coco coir is organic, whereas vermiculite is an inorganic alternative.

One of the best things I appreciate with vermiculite and coco coir is that they both absorb water effectively. This is important in the context of hydroponic gardening, specifically in systems that are not subjected to continuous water access (such as the nutrient film technique).

When vermiculite and coco coir have direct contact with water, they tend to absorb the water and store it inside each particle.

Due to vermiculite’s inorganic form, it may last longer compared to coco coir—making it a better alternative. Furthermore, coco coir has more and faster risk of pathogen development because it is organic.

   Learn more about this in our article on coco coir. 

5. Biochar

Biochar can be substituted with vermiculite due to its water-holding capacity. Both of them also have a pH that can elevate the pH, thus the need for liming in acidic soils decreases with their usage.

If you have an acidic gardening soil pH, adding a portion of biochar or vermiculite might be the best action you can do. This is because both agents have a high pH which can balance out your growing medium’s needed pH for the plants.

Why is it worthwhile to replace biochar with vermiculite?

1. Vermiculite is a cleaner growing medium to work with.
2. Vermiculite is a cheaper option.
3. Vermiculite looks better due to its shiny and brownish appearance.

2 Worst Growing Mediums to Substitute With Vermiculite

Running out of vermiculite and thinking what to replace it with? Well, here are 2 growing mediums to absolutely avoid due to their features being so different from vermiculite.

1. Hydroton

Vermiculite will not work as an alternative for hydroton. This is because they have completely different particle sizes, thus making them fit for different horticultural applications. For instance, hydroton is best for deep water culture hydroponics, whereas vermiculite works best as soil amendment.

Imagine substituting a toddler for a college professor in a university setting. Do you think the toddler will be able to handle it? In all honesty, I would scream a huge “NO!!!”

This is the relationship between vermiculite and hydroton. Because of the large size difference between the two, substituting hydroton with vermiculite is not recommended.

Vermiculite’s large grade only measures 8 mm at most, whereas hydroton can measure up to 16 mm in diameter! Considering this, vermiculite cannot serve the purpose of hydroton, especially in the hydroponic context.

   Discover more on hydroton in our article on hydroton vs perlite. 

2. Gravel

Gravel and vermiculite have different gardening uses. Gravel is best used as topdressing for succulents and growing medium for hydroponics whereas vermiculite is better suited as a soil amendment.

Aside from the difference in particle sizes, gravel and vermiculite also have extremely different water holding capacities.

Water can be held in vermiculite for a long time, whereas water can pass through gravel in a matter of seconds (less than 10 seconds). As a result, they could not be used interchangeably.

FAQS

What are the grades of vermiculite?

Vermiculite is available in the market in 4 grades—3 are horticultural grades namely, medium (2-4 mm), coarse (3-6 mm), and extra coarse (5-8 mm). These are known commercially as Grades 2, 3, and 4, respectively. The other grade is fine vermiculite, which is not ideal for gardening, since it is prone to being soggy.

Can you use vermiculite as a plant substrate?

Vermiculite can be used as a plant substrate due to its high water retention capacity and drainage. It is used commonly in the production of succulents, as well as water-loving plants such as ferns. Furthermore, the coarse grade of vermiculite can also be used as a soil amendment to improve the structure of the soil and its drainage.

Can you use gardening vermiculite in place of cat litter?

It is not recommended to use vermiculite instead of cat litter because the dust it contains may irritate the respiratory system of cats.

Can you use styrofoam instead of vermiculite?

It is better not to use styrofoam in gardening applications since it is extremely lightweight. When one waters the plants, this material tends to float to the top of the growing medium mix and further be blown away.

Summary of Growing Mediums to Substitute With Vermiculite

Vermiculite is a growing medium with excellent water-holding capacity and ability to enhance drainage of clay soils. Thus, it can be used as an effective substitute for horticultural grit, sand, pumice, coco coir, and biochar.

By contrast, it is not advisable to use vermiculite in replacement of hydroton and gravel. This is because they have different properties such as particle size and water-holding capacity.

Sources

• “Biochar as a Substitute for Vermiculite in Potting Mix for Hybrid Poplar” by Headlee, W.L. et al. in Springer
• “Horticultural Vermiculite” by N/A/ in J.P. Austin Associates, Inc.
• “Inorganic and Synthetic Organic Components of Soilless Culture and Potting Mixes” by Papadopoulos, A.P. et al. in Soilless Culture