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 to narrow 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 growth rates and quality of the harvested microgreens.

Not Really Soil - But Soilless Mix

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

soil for microgreens

However, to make reading (and writing) easier, when the text mentions soil, know that we're discussing are 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.

coconut coir as microgreen soil

Coco Loco Potting Mix

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

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

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

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

Coco Loco Ingredients

Coco Loco is composed of the following:

  • Composted forest humus,
  • coco coir,
  • perlite,
  • earthworm castings,
  • aged, composted bat guano,
  • Norwegian kelp meal,
  • oyster shell,
  • dolomite lime,
  • beneficial bacteria,
  • and mycorrhizae fungi.
  • 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.

    coco loco soil mix

    Happy Frog Potting Soil

    Happy Frog is produced by Fox Farms and is a peat moss based soil mix. We purchase a 2 cubic foot bag of Happy Frog to use in our always on-going 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:

  • composted forest humus,
  • sphagnum peat moss,
  • perlite,
  • earthworm castings,
  • aged, composted bat guano,
  • Humic acid (derived from Leonardite),
  • oyster shell,
  • dolomite lime,
  • beneficial bacteria,
  • and mycorrhizae fungi.
  • Fox Farm Happy Frog Soil Mix

    Soil Type Summary

    We want to see, by using side-by-side comparisons, 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 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.

    Soil for Microgreens Procedures

    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 tray that has been pre-wetted with the same volume of water. Here's how we plant the trays.

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

    Trays are placed under the same light in the same position and bottom watered 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 microgreens test.

    Soil for Microgreens Results

    Day 0 - Seeds Sown

    soil for microgreens test day 0

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

    coir soil test day 0

    Coconut Coir - Day 0

    coco loco soil test day 0

    Coir-based Soil - Day 0

    happy frog soil test 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 top of the seeded trays. The ambient temperature is between 75 and 80ºF, so a heat mat is not necessary.

    soil for microgreens test set up

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

    soil for microgreens test weighted trays

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

    soil for microgreens test tea towel for black out

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


    Day 2 - Seed Germination

    soil for microgreens test day 2

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

    soil for microgreens test - coir day 2

    Day 2 - Coconut coir - Can not tell if seeds appear to have less surface root hairs than the other two trays. However, root radicles seem to penetrate media more than other trays.

    soil for microgreens test coco loco day 2

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

    soil for microgreens test peat based media day 2

    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

    soil for microgreens test day 3

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

    pure coir soil media day 3

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

    coconut coir based soil media day 3

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

    peat based soil media day 3

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


    Day 4 - Remove from Blackout Period

    best soil for microgreens on day 4

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

    best soil for microgreens coir on day 4

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

    Best soil for microgreens coir based mix on day 4

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

    best soil for microgreens peat based mix on day 4

    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 (left most 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

    soil for microgreens first day under the light

    Day 5 - First under lights - Amazing how quickly microgreens green up once they receive light. Notice the difference in size between the coir-based media (left two trays) compared to the peat-based tray on the right.

    soil for microgreens Day 5 for coir

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

    soil for microgreen coir-based mix on Day 5

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

    soil for microgreen peat-based media on Day 5

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

    Side-view of the soil for microgreens test on Day 5

    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

    soil for microgreens compare on day 9

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

    coconut coir grown red acre cabbage day 9

    Day 9 - Pure Coconut Coir - Very nice tray of cabbage microgreens. Perfect for harvest.

    Red Acre Cabbage grown in coir-based media on Day 9

    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

    Red Acre Cabbage grown in peat-based media on Day 9

    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 a bit 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 that it's terrible to grow microgreens in a 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

    Soil for microgreens 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.

    microgreens grown in three different soil mixes

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

    comparison of soil for microgreen growing

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

    Which Soil Would You Use?

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

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

    Spawning Other Articles

    The results presented above will generate a few other articles.

    We especially are 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:

  • Coir-based Soil Mix Works Well on Quick Growing Microgreens - What About 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
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    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.

    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, then it might be more economical to buy coconut coir bricks online. We will see how inexpensive the coir bricks are in a future post.

    In summary, you can't go wrong with any of the three soils tested in this article. However, Coco Loco (coconut coir-based mix) appears to grow microgreens better than pure coir, or a 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 bags of coconut coir-based soil mix in the Home Microgreens Store. Click the Shop Now! Button below.

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