The Best Soil for Microgreens – Testing a Coir Mix and a Coir/Peat Mix

What is the Best Soil for Microgreens?

The soil you use significantly affects the size and quality of microgreens. This is why we spend much time and resources testing different soil media.

In previous articles, we tested several different soil types, coconut coir, a coir-based mix, and a peat-based mix, for how well they grew both quick-growing microgreens and slow-growing microgreens. 

Those articles can be accessed below in the highlighted box.

We haven’t trialed a soil mixture using coconut coir and peat together.

This article presents the results of a test between our favorite soil mix and a locally made soil mix containing coir and peat.

In the test, we planted the same mass of Waltham Broccoli and Genovese Basil seeds in the same volume of the two soil media to compare growth rates and the quality of the harvested microgreens.

We Call It Soil, But Really It’s a 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. 

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So when we mention soil, know we are discussing a soilless blend of ingredients.

The mixes shown above are the focus of this article. 

On the left is Fox Farms Coco Loco, and on the right is Greentree’s Growers’ Blend.

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 the soil we sell in small volumes. Coco Loco is sold in 2 cubic foot bags in hydroponic supply stores for between $21.00 and $25.00.

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 following image 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.

Greentree Grower’s Blend

Greentree makes their own mixes in Ithaca, New York. This is one of the reasons we would prefer to use this product as it supports the local economy. We bought the 1.5 cubic foot bag from their retail store for around $15.

The soil mix is well blended, has no clumps or large pieces of debris, feels soft and fluffy, and doesn’t compact in the microgreen tray.

It costs about the same as Coco Loco, but for me, it’s an hour longer drive each way to pick up the soil. That said, I rather buy a local product if it performs.

Growers’ Blend is labeled as organic, and this is a plus. I’m unsure about the sustainability mentioned on the label, may be more renewable than sustainable. 

Greentree’s products are sold in woven bags and are very durable. We also like the smaller 1.5 cu ft bags. 

The staff at the retail store are also very knowledgeable and friendly. 

As you can see in the first photo in the article, the peat in Grower’s Blend makes the mix a lighter shade of brown.

Growers’ Blend Ingredients

Growers’ Blend is composed of the following:

• coconut coir,
• sphagnum peat moss,
• perlite,
• earthworm castings,
• specially selected organic nutrients

• After blending, each batch goes through an aging process to encourage beneficial microbiological growth.
• The label says it’s a nutrient-rich, organic potting mix for container gardening.

The Microgreens Test

In the test soil, we’re growing broccoli and basil, a quick-growing and slow-growing microgreen, respectfully.

We expect, as we saw in our previous tests, that the nutrients in Coco Loco and Growers’ Blend might not be fully utilized during the short period the radish microgreens are in the soil.

But why not test the growth to make sure?

However, seeing how the coir/peat mix grows basil will be interesting. If you’ve read Which Microgreen Soil is Best for Slow-growing Microgreens? You know that the coir-based soil did the best right up to the end when the peat-based Happy Frog appeared to overtake the Coco Loco.

Soil Test Procedures

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

The same mass of Waltham Broccoli and Genovese Basil seeds is sown into each tray that has been pre-wetted with the same volume of water. Here’s how we plant the trays.

Soil for Microgreens Test – Blackout Period

During the blackout period, the exact weight is placed on each stack and covered to block light with the broccoli trays placed beneath the basil trays.

Once removed from blackout, the trays are placed under the same light in the same position and bottom watered. After an hour, if there’s excess water in the tray, it’s removed.

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

Soil for Microgreens Results

Day 0 – Seeds Sown

Day 0 Radish seeds sown on Coco Loco and Greentree Growers’Blend

Day 0 Basil microgreens sown and watered. Coco Loco on the left, Greentree Growers’ Blend on the right.

The seeds are germinated at room temperature, and even though the trays are stacked on a heat mat, it isn’t turned on.

Day 0 Trays are stacked, broccoli on the bottom and basil on top. A 2.5-pound weight is placed on each stack, and both are covered with a tea towel to exclude light.

Day 3 – Seed Germination

Day 3 Radish microgreens have germinated well and are ready to be placed under light. Broccoli grew great in both soils with no difference in height, density, or quality. This was expected.

Day 3 – Broccoli Ready for Lights

The broccoli and basil seeds germinated well in both soil mixes. As you can see, the broccoli is ready to be removed from the blackout and placed under lights.

As expected, the broccoli microgreens grew well in the coconut coir and coco/peat soil media. There are no discernible differences between the two trays of broccoli as it grew to harvest size.

Basil germinated well on both soil mixes as well. The basil remained in blackout for 5 days.

Day 5 – Basil Seedlings

Day 5 – Basil microgreens are ready to be removed from the blackout and placed under the lights. The Growers’ Blend didn’t hold the moisture as well as the Coco Loco soil mix.

Day 5 – Basil Ready for Lights

It might be hard to tell, especially since the Grower’s Blend is a lighter color than the Coco Loco, to begin with, but the Growers’ Blend did dry out a bit more around the outside edges, where the lid didn’t protect the soil moisture. 

We believe the Coir-based soil mix holds and disperse moisture better than peat or a coir/peat mix. 

The germination density is a bit better in the Coco Loco tray.

Day 27 – The Differences Are Apparent

Day 27 – Which Soil Mix Produced Better Basil?

Day 27 – The basil grown in Coco Loco is taller, more dense, and the leaves are larger.

Day 27 – Side view, Basil grown in Coco Loco on the left, and Growers’ Blend on the right. Better results from the Coco Loco.

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See The Effects Soil Has On Microgreen Growth

As you can see in the photos posted above, the soil significantly affects the size, quality, harvest time, and yield of microgreens.

Greentree Growers’ Blend is an excellent soil mix. They have all kinds of testimonials from happy customers, both retail and commercial growers.

Of course, every company will boost about their product and publish the love people give them. This is the reason we test soils.

The photos show that the basil grown in Fox Farms Coco Loco is taller and wider, and the leaves are bigger. Mounding on microgreen trays is common as those in the middle have more competition for light.

This is why seeding density is essential for microgreens. 

Best Soil For Microgreens – Discussion

Based on the tests we have run to date, we like Fox Farms Coco Loco soil mix. It absorbs water well and isn’t hydrophilic like peat moss and peat-based mixes. It drains well but still retains moisture for the plants. 

We also think the stringy composition of the mix allows better airflow to the microgreen roots. Coco Loco also doesn’t compact to the point where roots have difficulty anchoring in the soil substrate.

Coconut coir by itself absorbs water and is ideal for bottom watering. The additional products in the Coco Loco soil mix don’t interfere with this process, making it great to use with microgreens.

The natural fertilizers in Coco Loco appear to last long enough to boost the growth of longer-growing microgreens, such as basil and cilantro. Although, in the previous test, Happy Frog (another Fox Farm product) appeared to have more nutrients after the 4th week.

Soon we will test a natural ORMI-certified liquid fertilizer on longer-growing microgreens to see if it’s worth the cost and hassle. We’ll link to that article here when it’s published.

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Which Soil Would You Use?

Based on this article and the others that are linked in the article, what soil mix would you use? 

Do you have a favorite that you’d like us to test? We’d gladly do that if you have a suggestion.

In the meantime, we’ll keep testing other soils.

We believe in growing the most nutritious and healthy microgreens possible, and it all starts with the soil. 

Soil is better than any fiber mat we’ve tested by far. A soil mix that contains composted materials makes adding fertilizer unnecessary. 

So we will continue to use Fox Farms Coco Loco until we find better soil or one with the same growing properties at a more economical cost.

However, we wish that Fox Farms would sell Coco Loco in smaller bags so more people would use it. A two cubic foot bag is too much for most people. This is why we sell it in smaller quantities. 

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Spawning Other Articles

The results presented above will generate a few other articles.

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

Bricks of coir are the most economical soil to ship; we will experiment to find better ways to grow microgreens into pure coir without buying other soil additives.

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