Which Microgreen Soil Is Best For Slow-growing Microgreens?

Which Microgreen Soil is Best -Part 2

In the previous article, The Best Soil for Microgreens, we grew relatively fast-growing microgreens (Red Acre Cabbage) in three types of microgreen soil to see which is the best.

In that test, we decided that a coconut coir-based soil mix outperformed pure coconut coir, and a peat-based soil mix to use as a microgreen soil.

However, we haven’t dismissed pure coconut coir yet. The pure coconut coir performed well and may be less expensive to use as microgreen soil. Coir also holds water longer, so less time is spent caring for your microgreens.

comparing basil microgreens using fertilizer with home microgreens potting mix.

But What About Slow-growing Microgreens?

Can slower-growing microgreens such as basil grow in the nutrient-poor coconut coir for 20 or more days?

The coir and peat mixes are amended with natural, nutrient-rich ingredients. Will these nutrients help slow-growing microgreens grow faster and produce better plants?

In this article, we will plant and grow Dark Opal Basil in three microgreen soil media and document the results.

microgreen soil test

Day 0 – Planting Basil Seed in Microgreen Soil Media

home microgreens sells seeds

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microgreens planted in three different soil media

In the photo above, 1.0 grams of Dark Opal Basil Seeds are sown on three types of microgreen soil media. From left to right, pure coconut coir, a coir-based potting mix, and a peat-based potting mix.

Notice the mucilaginous coating on the seeds. You can see the white gel-like substance on the seeds. These seeds have been sown and wetted with water before being placed in their blackout period.

basil seeds are mucilaginous

The basil seeds and microgreens will be germinated and grown exactly as the cabbage microgreens were in the test described in The Best Soil for Microgreens

All of our microgreen soil and jute media articles are listed below if you’d like to compare this test with the others.

The three microgreen soils are shown in the same order in the photos below.

The first tray contains pure coconut coir.

Second, is a coconut coir-based potting mix produced by Fox Farms called Coco Loco or Bush Doctor Coco Loco.

Lastly, a peat-based potting mix, again produced by Fox Farms, called Happy Frog. 

Remember, pure coconut coir is nutrient poor, and we question if plants can grow well in it for 20 or more days without adding liquid fertilizer.

The other two potting mixes contain natural mineral and organic amendments. These amendments are listed in the previous article, The Best Soil for Microgreens if you’re curious about the amendments.

We believe these two potting mixes will perform better than pure coir.

Below is a chronological sequence of photos showing the basil growth stages during the test.

Day 4 – Basil Microgreens Placed Under Light

Red Rubin Basil after 4 days in blackout

On day 4, the trays of basil are removed from the blackout period and spaced out in a watering tray under an LED light with a spectrum of 4,000K.

The growth of the microgreens is similar, but those grown in pure coir are less leggy, more upright, and appear better rooted in the microgreen soil media. This is identical to the first test, where the cabbage microgreens anchored themselves quicker in the coir than the other media.

Day 9 – Equal Growth in the Cotyledon Stage

Three soil media test

Day 9 – Red Rubin Basil planted left to right in pure coconut coir, Coco Loco Potting Mix, and Happy Frog Potting Mix.

Day 9 – Pure Coconut Coir

Red Rubin Basil in coco loco

Day 9 Coco Loco Mix

Red Rubin Basil in Happy Frog

Day 9 Happy Frog Mix

Growth during the cotyledon stage is about the same for all three microgreen soil media.

However, you can see that the basil grown in peat-based microgreen soil does have slightly smaller leaves.

The faster-growing cabbage microgreens in the first test showed the same pattern but with more variance. 

Also, the peat-based microgreen soil media is dryer than the coir-based trays (the first photo shows this well). We bottom-water the microgreens in a level watering tray during the test. Therefore, all three potting mixes have the opportunity to draw up equal volumes of water. 

You can see that peat doesn’t draw water as well as coir.

Grow Your Own Microgreens

Day 12 – Growth Differences Appear

Dark Opal Basil 12 days after planting

Dark Opal Basil 12 days after planting. Same order as the previous photo.

Basil in coconut coir

Day 12 Basil’s first true leaves barely forming between cotyledons.

Basil planted in Coco Loco Mix

On day 12, the first true leaves have formed and are starting to grow out.

Basil microgreens 12 days after planting in Happy Frog Mix

Day 12 plants are very similar to those planted in pure coconut coir.

The microgreens were harvested in the Red Acre Cabbage experiment on Day 9. Both coir-based soil media produced more cabbage microgreens than peat-based soil media.

But here on Day 12, the basil in pure coconut coir is lagging behind both potting mixes.

The basil microgreens growing in pure coconut coir (first close-up photo) haven’t developed true leaves. 

As you can see in the middle photo, the first true leaves have not only formed but are growing more prominently in the coir-based potting mix than the others.

In the last photo, you can also see small true leaves forming on the basil growing in the peat-based mix. 

Is the reason for the developmental difference because the smaller basil seeds (compared to cabbage seeds) don’t contain as much starch? And the basil seedlings use the available nutrients in the potting mixes to grow sooner than the cabbage?

We believe so.

We also believe the basil plants are larger in the Coco Loco potting mix because plants seem to develop roots quicker in coir than peat.

Day 19 – Better Color & Size in Coir-based Potting Mix

Red Rubin Basil after 19-days

On Day 19, the basil in the nutrient-poor coconut coir is falling behind the mixes.

The middle tray is the basil grown in the coir-based microgreen soil. It’s growing better (more color) and larger than those grown in pure coir (left tray) and a peat-based potting mix (right tray). 

The basil grown in pure coir lags behind the other two in development, size, and color.

The peat-based media basil isn’t far behind the middle tray. We’d be happy with those microgreens if the middle tray weren’t there.

Day 25 – How Things Change – Too Little Too Late?

Red Rubin Basil 25 days after planting in, left to right, pure coconut coir, Coco Loco Mix, and Happy Frog Mix

On Day 25, the basil microgreens planted in the soil mixes (the right two trays) are growing well. The left tray, planted in pure coconut coir, remains small.

Red Rubin Basil microgreens

Side view of the basil microgreens on Day 25.

Basil microgreens planted in coconut coir

Basil microgreens planted in pure coconut coir after 25 days.

Basil microgreens grown in Coco Loco Mix after 25 days

Basil microgreens grown in Coco Loco Mix after 25 days.

Basil microgreens grown in Happy Frog Mix after 25 days

Basil microgreens grown in Happy Frog (peat-based) Mix after 25 days.

Six days later, the basil microgreens grown in the peat-based potting mix have overtaken the coir-based potting mix in size. But they haven’t colored as nicely. 

The microgreens are grown in pure coir lag behind both potting mix microgreen soil media.

We aren’t quite sure why the turn of events. 

From what we’ve read, both peat and coir lack nutrients. The only difference in amendments between Coco Loco and Happy Frog is kelp and leonardite, respectfully.

One would think that kelp would provide more plant nutrients (NPK) than leonardite, which is more a soil conditioner than fertilizer.

Maybe the humic acids that leonardite supposedly adds to the mix are the difference?

I will have to put more thought into the reasons.

Which Microgreen Soil Media Is Best for Slow-growing Microgreens?

Slow-growing microgreens, harvested after 20 days or longer, appear to do better in a peat-based potting mix. The coir-based potting mix is not quite as good as the peat-based mix.

Pure coconut coir is not the microgreen soil media to use for slow-growing microgreens.

Where Does This Leave Us with Microgreen Soil?

Right now, at least after this experiment, we’ll continue to use the coir-based potting mix (Coco Loco) for all of our microgreens.

Pure Coconut coir can’t grow slow-growing microgreens, and the peat-based potting mix doesn’t grow quick-growing microgreens very well.

Coco Loco grows both quick-growing and slow-growing microgreens best on average. So instead of buying Coco Loco and Happy Frog, we’ll plant slow-growing microgreens in Coco Loco and let them grow for a couple of days.

However, we want to run more tests and experiments on this topic. Below is a list of articles we plan on publishing. We may also add to this list as we go.

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

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Our Favorite Microgreen Soil 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 we use 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. All of them will grow microgreens; it’s a matter of how long they need to stay in the tray.

However, Coco Loco (coconut coir-based mix) grows quick-growing microgreens better than the other two. Also, slow-growing microgreens do well in it as well.

The peat-based Happy Frog potting mix grows slow-growing microgreens quicker than Coco Loco and pure coir.

On average, Coco Loco is much better for fast-growing micros and just a bit behind Happy Frog on slow-growing microgreens. We’ll deal with that and stick with Coco Loco for now.


We now have our own blend of potting mix. It is a coconut coir-based potting mix like Coco Loco but with other additives. Use the button below to visit the Home Microgreens Store.


  • Todd

    Todd is the founder of Home Microgreens & the Home Microgreens store. He also writes for several other websites, including MyViewFromTheWoods.com. Todd worked at a large farm market, garden & nursery center for 20 years. Somehow he snuck off to become a geologist and professor before coming back to his senses to write & lecture about microgreens and gardening. When not at the computer, he can be found in the garden, trout stream, or mountain trail with his new Springer Spaniel Caden.

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