The Best Soil for Microgreens

Soil for Microgreens – Which Media is the Best?

In a previous article, we showed without a doubt that growing microgreens in the soil is way better than on jute mats.

The next obvious step is to evaluate soil media to see which works best. Or at least begin the process of narrowing down the choices.

We planted the same mass of Red Acre Cabbage microgreen seeds in the same volume of three soil media, pure coconut coir, a premium coconut coir-based mix, and a premium peat-based mix, to compare the growth rates and quality of the harvested microgreens.

Not Really Soil – But Soilless Mix

When we say soil, we really mean using soilless media. Soil, by definition, contains a mixture of organic matter, minerals, gases, liquids, and organisms. 

However, to make reading (and writing) easier, when the text mentions soil, know that we’re discussing the following soilless mixes as shown above from left to right.

Coconut Coir

The first media is coconut coir (click the link for more information). The coir is loosened from a Plantonix brick by using water to moisten, but not saturating, the coir.

Click any image in this article to expand the size and get a better look.

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Coco Loco Potting Mix

Fox Farms produce Coco Loco and is a coconut coir-based potting mix. We use this soil mix in our microgreen trays and the soil we sell in small volumes. We currently purchase Coco Loco in 2 cubic foot bags for between $19.50 and $21.00.

We wouldn’t expect anyone to purchase Coco Loco on Amazon because of the price (due to shipping a large bag), so we sell smaller bags for the home microgreen grower.

However, if you want to look, you can click the next image or this link.

When you purchase any coir product, use one that professional growers would buy, as the quality will improve.

Coco Loco Ingredients

Coco Loco is composed of the following:

The coir is triple-washed to ensure a quality product with low salt content.

The mix is sterilized; not sure how that works with the bacteria and fungi. We’ll research this more and let you know.

Happy Frog Potting Soil

Fox Farms produce Happy Frog and is a peat moss-based soil mix. We purchase a two cubic-foot bag of Happy Frog for our ongoing microgreen tests. We bought the bag from a hydroponic supply store for $20.

Happy Frog is sold in smaller bags. The link below and the image adjacent will take you to Amazon, where Happy Frog is sold in a 12-quart bag. 

See Happy Frog peat moss-based potting soil mix in a 12-quart bag on Amazon.

Happy Frog Ingredients

Happy Frog is composed of the following:

Soil Type Summary

By using side-by-side comparisons, we want to see which soil is better for microgreens. We are testing three soils, pure coconut coir (a sterile, non-nutrient-based media), a coconut coir-based potting mix, and a sphagnum peat-based potting mix.

The test is limited to three soil media types due to space restrictions. Other media, such as vermicompost, will be tested for similarity with those that show the most promise in this test at a later date.

The Soil for Microgreens Test

In the test soil, we’re growing Red Acre Cabbage microgreens.

We consider cabbage a quick-growing microgreen. We also realize that the nutrients in Coco Loco and Happy Frog might not be fully utilized in the short period the cabbage microgreens are in the soil.

Therefore, we will run a second test with a slower-growing microgreen, such as basil. We will, of course, link that article here when it’s published.

Similar planting trays (same size, number of watering holes, etc.) are filled with each of the soil media types.

The same mass of Red Acre Cabbage seeds is sown in each pre-wetted tray with the same volume of water. Here’s how we plant the trays.

The trays are then covered with the same weight during the blackout period.

Trays are placed under the same light in the same position and bottom water in a larger 10 by 20 tray. More water is added to the watering tray than needed. After an hour, the excess water is removed from the watering tray. 

Below are the results of the soil for the microgreens test.

Soil for Microgreens Results

Day 0 – Seeds Sown

Left to Right – Coconut coir, Coco-based soil, peat-based soil.

Coconut Coir – Day 0

Coir-based Soil – Day 0

Peat-based soil – Day 0

Soil for Microgreens Test – Blackout Period

All three trays of soil media planted with Red Acre Cabbage were placed in a 10- by 20-inch tray. A plastic cover is placed over the seeds, and a two-and-a-half pound weight is added to the top.

Light is excluded during the blackout period by placing a tea towel on the seeded trays. The ambient temperature is between 75 and 80ºF, so a heat mat is unnecessary.

Trays placed in a 10- by 20-inch watering tray

Two-and-a-half-pound weights were added to the top of the tray covers.

A tea towel covers the trays, and the light is shut off after taking the photo.

Day 2 – Seed Germination

Comparison photo of trays on Day 2. Covers were removed for a photo, then the trays were placed back into the blackout.

Day 2 – Coconut coir – I cannot tell if the seeds appear to have fewer surface root hairs than the other two trays. However, root radicles seem to penetrate the media more than other trays.

Day 2 – Coir-based media – Numerous root hairs on radicles but less penetration into soil media than those on pure coir.

Day 2 – Peat-based media – Similar to coir-based media, many root hairs on root radicle, but less penetration into soil media.

Day 3 – Rooted Seedlings

Comparison photo of Red Acre Cabbage microgreens on Day 3. Left to Right: Pure coir, coir-based soil media, peat-based soil media. The cover was removed for the photo then the trays were placed back into the blackout.

Day 3 – Pure coconut coir – Red cabbage is well rooted into soil media. The plants are the same height and growing vertically.

Day 3 – Coir-based media – Many cabbage roots have not penetrated deeply into the soil. Many root hairs still are above the soil surface. More plants have bend stems than pure coir seedlings.

Day 3 – Peat-based media – Less root penetration into soil media than both coir trays. The soil media on the edge of the tray is drier than the previous two trays.

Day 4 – Remove from Blackout Period

Comparison photo on Day 4. Some key differences will be explained in the close-up photos.

Day 4 – Pure Coir – Notice how erect these plants are. They have developed deep, strong roots so the plants can push the weight up off the tray.

Day 4 – Coir-based Mix – Fairly similar to pure coir. However, the plants are not quite as erect.

Day 4 – Peat-based Mix – Notice how these plants appeared crushed or growing more prostrate than the previous two trays. Most likely the roots aren’t as well anchored and able to push the weight up off the tray.

Day 4 – Differences Are Apparent

There are noticeable differences in the rooting behavior of the cabbage seedlings as early as Day 2, and on Day 4, the rooting behaviors have expressed a physiology response in the plant.

The photos were taken immediately after the weights and covers were removed from the trays and blackout.

In the first photo, you can see that the seedlings in the pure coconut coir (leftmost tray) and, to a slightly lesser extent, the plants in the coir-based soil (middle tray) are more upright. 

We believe the more upright behavior is because the roots have an easier time establishing themselves in the coir than peat. The seedlings in the coir and coir-based media are better anchored, allowing the plants to lift the weights and straighten out their stems.

The seedlings growing in the peat-based media can not leverage the soil to lift the weight and straighten themselves.

The trays will now be removed from the blackout period, and the LED light will be turned on for 15 hours a day.

Day 5 – First Day Under Light

Day 5 – First under lights – How quickly microgreens green up once they receive light is amazing. Notice the difference in size between the coir-based media (left two trays) and the peat-based tray on the right.

Day 5 – Pure Coir – Very vibrant tray of Red Acre Cabbage.

Day 5 – Coir-based media – Very similar to the pure coir tray in height, leave size, and plant density.

Day 5 – Peat-based Media – The plants in the peat-based media are much smaller, both in height and leaf size.

Day 5 – Side-view – You can see the size difference between the coir-grown microgreens (left two) compared to the peat-based grown microgreens (right tray) in this view.

Day 9 – Skip To The End

Day 9 – Let’s face it, all three trays look good. They grew out well, but it appears to me that the middle tray is larger than the other two.

Day 9 – Pure Coconut Coir – Lovely tray of cabbage microgreens. Perfect for harvest.

Day 9 – Coir-based Media – Slightly large plants than the pure coir-grown microgreens. They’re starting to fall over. Best if harvested on Day 8. The most mass of microgreens of all three trays

Day 9 – Peat-based Media – Of the three trays, the plants are smaller. Not that the plants aren’t healthy or in good shape, just behind the other two in growth.

Best Soil For Microgreens – Discussion

It’s hard to tell from the photos which tray grew the best. But the images below are better because of the white background. 

Microgreens will grow well in all three media types. We wouldn’t call any of the trays bad. But the coconut coir and coir-based soil media grew larger microgreens over the nine days. 

That isn’t to say it’s terrible to grow microgreens in peat-based soil. Only a different growing method might be needed.

But using the Home Microgreens growing method, microgreens grow better in coconut coir or coir-based soil media.

The photos below show the results in a better light.

Microgreen Size Comparison

Day 9 – Left to Right – Red Acre Cabbage grown in pure coconut coir, Coco Loco, a coir-based soil mix, and Happy Frog, a peat-based soil media.

Day 9 – Oblique view of the three trays of microgreens. Again, pure coir is on the left, coir-based media is in the middle, and peat-based media is to the right.

Day 9 – Side-view of the three trays of microgreens.

Which Soil Would You Use?

If you grow microgreens at home or commercially, let me know what soil you use and why. Even if you use jute or other mat material, please comment below and tell everyone why.

Depending on the growing methods and probably 25 other variables, there are many ways to grow microgreens. However, based on the results, we believe a coconut coir-based media is best for our recommended way of growing microgreens.

Spawning Other Articles

The results presented above will generate a few other articles.

We are especially interested in how well seeds germinate and grow into the coconut coir.

Links to the articles will be included in this post once they’ve been published. The topics we’re thinking about now, to name a few, will be:

• Soil for Microgreens – Which Media is the Best?
• Which Microgreen Soil is Best for Slow-growing Microgreens?
• What is the Volume & Cost Difference Between Coconut Coir Bricks & Bagged Coir
• Comparing the Wetting Characteristics of Coir to Sphagnum Peat-Based Soil Media
• How Many Quarts of Material Are in A Coconut Coir Brick
• How to Use Coconut Coir in Inside & Outside Gardening
• Do the Soil Additives in Soil Mixes Improve Microgreen Growth
• Comparing Coconut Coir, Coir-based Soil Mix, and Vermicompost for Microgreens

Don’t miss a future article; click the button below to receive updates.

Our Favorite Soil For Microgreens Is…

We prefer to use the coconut coir-based Coco Loco Potting Soil for microgreens. We think it allows for the perfect amount of water uptake without staying too wet. Also, the microgreens root quickly into the media allowing the young plant to anchor and absorb nutrients as the plant grows.

Note: We now have our own blended microgreen potting mix. You can check it out here and see all of the positive reviews!

Home Microgreens Potting Mix

We like the looseness of the bagged soil, and nothing has to be done to the soil before using it (like hydrating coconut coir bricks).

That said, if we couldn’t purchase Coco Loco locally, buying coconut coir bricks online might be more economical. We will see how inexpensive the coir bricks are in a future post.

You can’t go wrong with any of the three soils tested in this article. However, Coco Loco (coconut coir-based mix) grows microgreens better than pure coir or peat-based soil mix.

What soil mix or fiber mat do you use to grow microgreens? Leave a comment and let us know! We can all learn from each other.

You can purchase small coconut coir-based soil mix bags in the Home Microgreens Store. Click the Shop Now! Button below.

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