Peat Moss vs Coconut Coir – The Reason to Hate One & Love the Other

Soil Mix Conundrum – Peat Moss vs. Coconut Coir

If you grow microgreens in a soil mix,  you have two choices, peat moss or coconut coir.

Neither grows microgreens very well by itself (more on this later). This is why we use soil mixes. The peat or coir makes up the base or bulk of the mix, and other amendments are added to improve fertility.

Environmental, social, political, cost, renewability, and sustainability issues with peat moss and coconut coir exist. Those issues will be addressed in other articles because they are essential to understand and deserve a whole article for discussion. 

But for the sake of arguing over those matters right now, let’s assume that all things are equal and look at the growing propensity of these two soil materials.

Peat Moss vs. Coconut Coir – Growing Microgreens

As mentioned, neither grows microgreens very well by itself. They are, for all intents and purposes, nutritionally inert for plants. 

Though we haven’t tried to grow microgreens in pure peat moss (yet), we have attempted to grow microgreens in pure coconut coir. It didn’t turn out that well.

You can read and see photos of that attempt in this article: The Best Soil for Microgreens.

The title of that article seems to be the end all be all for the best soil. But that isn’t the case because we haven’t tested all soil mixes, and we also want to experiment with organic fertilizers in the cheaper but inert soil types.

Audio Presentation of the Peat vs Coir / Love & Hate Debate

In the podcast, we talk about our problems when using peat moss-based soil mixes. This is the Microgreen Podcast Episode 003.

What About Growing Microgreens Without Soil?

We tried that too. So far, our testing has shown that soil outperforms mats by a long shot.

You can see the results of that testing by clicking this link.

Plus, some microgreen seeds can’t be grown hydroponically or on mats.  

This shouldn’t be a surprise because where do seeds grow best in nature? In soil, not on cloth, hemp, cotton, some unique fabric, or water.

However, we do have some new (to us) bamboo mats to try. At Home Microgreens, we try to keep an open mind, and if testing shows our previous results to be wrong, we will change our opinion.

What is Soil Mix?

Since peat moss and coconut coir are nutrient-poor, other amendments are added to improve fertility and drainage.

Each soil manufacturer has their own blend of amendments. The amendments are usually perlite and composted or aged wood products, composted manure or another nitrogen-rich product, and mineral additives.

The peat moss and coconut coir provide a relatively inexpensive, sterile, inert bulk product.

Pin the Image Below to Your Pinterest Microgreens Board

How Peat Moss and Coconut Coir Contribute to Soil Mixes

Both are natural inert organic bulky material perfect for soilless potting mixes. Each holds 8 to 10 times its weight in water.

Holding water is vital for any potting mix, especially in containers.

They also resist breaking down (rotting) and keep their volume. Even though both can be compressed, they remain relatively fluffy once loosened.

Since peat moss and coconut coir can be compressed into bales, it is easier and cheaper to ship the product.

Peat moss is easily mined for vast deposits, and coconut coir is a waste product that needs to be transported away from the processing plant anyway—best to transport it to a facility that can use it rather than used as landfill material.

Since the material is easily obtained and the volume can be shrunk for transport, these materials become less expensive to use as the base for soil blends.

The price of each depends on your location relative to the source of the material. About 80% of the world’s peat moss comes from Russia and Canada.

While 90% of coconut coir comes from India and Sri Lanka.

It’s a Curse and a Blessing, aka a Love / Hate Relationship

Here comes the Love-hate aspect of the peat moss vs. coconut coir debate – at least for us. 

Let’s face it microgreens have it tough. They really do. We overseed them in shallow trays, grow them in a warm area on some open metal rack, and often (at least commercially) have fans blowing on them.

All those plants are looking for water, and the shallow trays quickly become root-bound. The small soil volume in those trays must hold water but still allow for oxygen exchange.

Due to their ability to hold water, peat moss and coconut coir are the perfect media for growing microgreens.

But let’s look at the video below to see if this is true.

By the way, the peat-based and coir-based soil mixes in the video are produced by the same company and mostly contain the same amendments. They are very similar, except one uses peat and the other coconut coir.

Video – Wetting Microgreen Soil Mixes

Did You See That?

What a mess.

Besides the muddy beginnings of peat moss, the problem is much more profound.

Here Are The Reasons We Hate Peat Moss

1. Who Has the Time?

When I’m planting microgreens, I don’t care if it’s one tray or ten; I want it done. 

Yes, you can sprinkle the seeds before the water is soaked into the peat moss. But you can’t spread the seeds if you clump them together by mistake. 

That sticky peat moss mud on my finger isn’t the best substrate for pushing seeds around and spreading them out.

We bring this up because you will see how long it takes for water to soak into an organic peat-based soil mix manufactured by a national and well-liked brand in a soon-to-be-released article.

It’s ridiculous. We wouldn’t publish the article if it weren’t a national brand. But we don’t want anyone buying this soil and must put up with it.

We’ll link the article here when it’s published.

2. What Takes Time Going Down, Takes Time Coming Up

We believe entirely in bottom-watering microgreens once they have started growing.

So if it takes that long for water to soak into the peat moss, imagine how long it will take to wick up from the bottom.

In the video, water had gravity to help it soak in, but it sat there. So think about the problems water will have fighting gravity to wick upward when we bottom water a microgreens tray.

Now, we’ll have to give peat moss some benefit of the doubt.

Once wet, peat moss more readily takes on water. So if it stays damp, water will absorb and move through the soil column quicker.

But what if your microgreen trays do dry out?

Yeah, you’ll be forever rewetting that peat moss.

3. Too Much of a Good Thing

According to our research, peat moss and coconut coir hold about the same water per unit weight. Now we’re unsure if an average peat moss and coco coir tray weigh the same.

We also don’t know what the experts mean by “hold water” Does this mean the weight of water absorbed by the media? Or does it include the water held between the media particles?

Big difference. We think what they mean is how much water the organic fibers absorb.

But we do know that peat moss pores are much smaller, capillary forces are higher, and cohesive attraction and adhesive forces are more significant.

So a tray containing a peat moss mix will retain more water than a tray full of a coconut coir mix. We know this because we’ve watered hundred of trays, and water more readily drains from those full of a coir mix. 

In other words, peat moss doesn’t drain. 

You’d think this is what we are after, more water retention. However, we do need pore space for the soil to hold air. We need the water to wet the media and drain through, so air can reenter the soil media.

Coconut coir has longer, coarser strands than peat moss does. Water will run down these strands and drain. The larger spaces between the fibers reduce capillary forces and leave more room for air. 

Too Much Moisture Is Bad During the Blackout Period

Remember what we recommend when seeding a tray of microgreens. 

Don’t wet all of the soil. 

We only want the upper surface (top 1/8- to 1/4-inch) to be wet. 

We either tightly cover the soil or put a dome over the soil during the blackout so that a little moisture will go a long way.

Only after the plants are under the lights do we bottom water. 

Peat moss tends to hold too much water against the seeds and takes up water slower when we do bottom water.

Those Are Our Reasons to Love One and Hate the Other

In our opinion, the peat moss vs. coconut coir debate is over. 

We hate growing microgreens in peat-based soil mixes. Sometimes, such as during the CoVid19 shutdown, we had no choice. We had to use what was available and adapt to using peat-based blends. 

It took us longer to plant our trays of microgreens; they did not grow either; we had to change our methods to stop fungus and lengthen the grow times to get the exact yield.

It was cheaper on the wallet, but that was about it.

It isn’t that you can’t grow microgreens in peat moss. Thousands do.

But it’s easier to grow microgreens in coconut coir-based mixes.

We love growing microgreens in coir mixes because the process is faster, and easier, and the yields are larger using our methods.

Our Preferred Soil Mix

Here’s our preferred soil mix. This soil is included in the Home Microgreens Kits, and we also use it to grow trays of retail microgreens.

What’s Your Experience?

What do you use to grow your microgreens? 

Have you had good luck with peat moss? With coconut coir? Maybe mats? 

Let us know in the comment section. We can learn from each other.