What is the Best Soil for Microgreens?
The soil you use has a significant effect on the size and quality of microgreens. This is why we spend a lot of time and resources testing different soil media.
In previous articles, we tested several different soil types, coconut coir, 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.
What we haven't trialed is a soil mixture using both 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 both coir and peat.
In the test, we planted the same mass of Waltham Broccoli seeds 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 Soilless
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.
So when we mention soil, know that 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 is also the soil that we sell in small volumes. In hydroponic supply stores, Coco Loco is sold 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), 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:
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, and feels soft and fluffy, and it 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, this is a plus. I'm not sure about the sustainability mentioned on the label, maybe 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,
- 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, it will be interesting to see how the coir/peat mix grows basil. 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 of 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 same amount of 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
The seeds are germinated at room temperature, even though the trays are stacked on a heat mat, it isn't turned on.
Day 3 - Seed Germination
Day 3 - Broccoli Ready for Lights
The seeds, both broccoli, and basil, 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 both 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 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 that the Coir-based soil mix does hold and disperse moisture better than peat or even 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?
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See The Effects Soil Has On Microgreen Growth
As you can see in the photos posted above, the soil has a significant effect on 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 from retail and commercial growers.
Of course, every company is going to boost their product and publish the love people give them. This is the reason we test soils.
Looking at the photos, you can see 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 the in the middle have more competition for light.
This is why seeding density is essential for microgreens.
Best Soil For Microgreens - Discussion
At this point, 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 a hard time 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 infer 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 a better soil or one with the same growing properties at a more economical cost.
We do, however, 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.
Spawning Other Articles
The results presented above will generate a few other articles.
We especially are 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 having to buy 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:
Microgreen Kits & Seeds
Grow Microgreens in Your Home!
Shop for Kits, Equipment, and Seed.