You’re on the road to growing microgreens, but there are a lot of questions.

What is the best growing mediums for microgreens, and how will it affect your overall yield?

Do certain microgreens need certain soils?

There are a lot of questions.

Fortunately, however, there are also a lot of answers despite indoor urban farming being a relatively new concept in agriculture.

In this article from HerbSpeak, you will learn everything you need to know about different growing mediums, or “soils” for microgreens and which is best for your set-up, whether it’s at home on the countertop or spanning a commercial greenhouse.

What Microgreen Growing Mediums Are Available?

When you first start growing microgreens, it can be difficult to find all the answers. Even a small countertop kit is an investment, and you want to make sure your money is well-spent. Fortunately, there are many ways you can use the baby plants once they are grown. (1) First, you must decide on how to grow them.

In fact, you might be surprised to learn that there are many more growing mediums than your everyday potting soil mix, and each type of substrate has its own pros and cons. Learning about how different soil types affect the plants is just one of the many benefits that microgreens provide growers.

The comparison table below will help you easily choose between different growing mediums. For more detail on choosing a substrate for your micro greens, continue reading.

Factors to Consider When Selecting a Growing Medium 

When gardening outside, you know that plants will require nutrients, so you add compost to the soil, aerate it with worms, and carefully water it.

With microgreens – or any urban vertical farming – humans have such little experience that it can lead to a host of questions about what is good and not. (2) Indoor farming can change the needs of plants, and you must find a balance in what works best for your crops.

1. Cost

If you are intending to sell your microgreens, even to recoup the costs of a hobby, then you will need to take cost into consideration. Without a good profit margin, you have to decide whether the work is worth your time.

If you are growing microgreens for your personal consumption, then you might want to keep your spending in check, keeping nutrients in your diet for a lower cost than supplements.

Soil and hydroponics are two of the more expensive growing mediums for microgreens, while hemp and coir are on the lower end of the cost spectrum.

The reason for this is that soil is typically treated with nutrients, and it is heavy to transport. At each step of the supply chain, companies must make money on a bag of heavy, nutrient-laden dirt. This means that premium soil will easily cost twice or three times as much as other mediums.

Coco coir, on the other hand, is less expensive because it is made from coconut fibers and then compressed into a strong brick.

Yes, each step of the supply chain must also make money here, but it costs a lot less to store and transport, and it can expand greatly in volume, giving you just as much substrate to work with as you would with a heavy bag of soil at a fraction of the cost. The downside is you will need to add nutrients if you are growing micros that require more than 12 days or so until harvest – more on that below.

2. Water Retention

The water retention in your soil is an important aspect to balance, especially if you are trying to save costs by creating a custom mix.

Too much moisture, and you risk root rot, mold, damping off, and pests.

Too little moisture, and you risk the plants drying out, wilting, losing growth, and dying.

This is especially true if you intend to use a shallow tray or container when growing microgreens, as the thinner the soil level, the faster the water will evaporate.

Likewise, the soil must also be able to properly drain excess water and allow enough oxygen through to the roots.

 3. Nutrients

There is a common misconception that microgreens don’t need nutrients to grow, and this is technically not true.

All plant seeds do contain a bare minimum amount of nutrients that are intended to help the plant grow until it can develop roots and begin getting nutrients through the soil. This only gets the plants so far, however.

All plants need nutrients to survive and grow. It is the basic necessary component in growing anything; water is required to help the plant slowly synthesize nutrients from the sun, but a plant cannot live in sunlight alone.

It must also gather nutrients from the soil, as only some nutrients are available through the soil. The root tips are some of the most sensitive parts of the plant, able to detect vibration, moisture, and nutrients in the soil and grow in that direction.

Not every soil is created equal, and the lower-end soils will leave you with pesky nutritional deficiencies in the crop.

With soilless mediums, you are removing the plant from any source of nutrients that it could absorb. For most microgreens, this is acceptable because they are harvested in under 10 days, before the seed’s internal stores run dry.

A lack of nutrition becomes a problem, however, once you venture into longer-growing micros like herbs, often taking between 20 and 25 days to harvest.

What Are the Best Growing Mediums for Microgreens?

There are so many options to choose from, and microgreens growers are experimenting with new growing mediums everyday it seems.

Microgreens have such a short growth cycle that it’s tempting to experiment yourself, as well! You’ll see growers using everything from paper towels to pine needles and leftover coffee grounds (acidity and pH permitting) in their mixes.

It’s a great excuse to try something new, but first it’s important to establish yourself with something to give you a baseline of efficacy.

There are a few common substrates that a lot of growers swear by. It’s up to you to figure out which medium works best for you and your seeds.

Soil

Soil is the classic way to garden, so many microgreens farmers have put it to use. Premium organic soil is most often recommended, and I’ve had a great deal of success with Happy Frog soil in particular, giving me a great yield, good taste, and a vibrant crop. This soil is fairly sterile, so it is ideal for growing indoors where pests might be a concern.

CONS

• Costly up-front expense.
• Messy and difficult to work with indoors.
• Heavy bags take up a lot of room.

Coconut Coir

Coco coir is one of the most versatile mediums because it feels and acts like soil, while retaining more water than soil for a much lower price. With most microgreens, this is all you need. Outside of potassium and sodium, coco coir is generally low in nutrients.

CONS

• Takes up space once rehydrated.
• Can be difficult to saw bricks apart for smaller portions.
• Longer-growing micros will need nutrients added to the water.

Hemp Mats

These mats are well-known for their convenience. They are easy to roll out, cut, and fit into the tray. I’ve had the most success with Terrafibre brand mats. This is not a substrate I would recommend for someone just starting out as it is very easy to over-water, but the loose fibers do come in handy for keeping seeds evenly distributed.

CONS

• Different brands give you different yields.
• Hemp mats make it easy to over-water.
• Usually necessary to buy online.

Biostrate

Biostrate is a blend of “biopolymers” and natural fibers. Essentially, this medium is part synthetic fiber and part natural fiber, designed to help regulate water for many different hydroponic applications.

CONS

• Not sustainable due to synthetic fibers.
• Somewhat easy to over-water compared to other mediums.
• Expensive up-front cost.

Vermiculite

Vermiculite is a naturally occurring mineral that expands once heated. This is typically added to soil mixtures to increase soil drainage and encourage root health in adult plants, but bucket-type microgreens setups can benefit from vermiculite as a nutritive pH-neutral medium.

CONS

• Difficult to sterilize and re-use.
• Difficult to judge moisture, due to top layer drying faster than bottom.
• Smaller seeds can get lost in the medium if bumped or shaken during germination.

Paper Towels

You might have seen another microgreens grower trying out paper towels as an affordable solution to a hydroponic growing medium. After all, the seeds only need to germinate and grow a little. Still, paper towels are all made differently, with different fibers, ply, and weaves, so there are a lot of variable results.

CONS

• Variable effects based on brand and ply.
• Not all paper towels are food safe.
• Easy to over or under water quickly.

HerbSpeak’s Recommendation:

Overall, the HerbSpeak recommendation goes to coconut coir.

Why?

There were four main factors that went into this decision:

• It is less expensive than soil.
• It retains water well.
• It mixes well with other materials for custom mixes.
• It is easy to add nutrients to if needed.

Overall, growing microgreens in coconut coir has proven to be a much more rewarding and hassle-free experience, especially if you are doing your growing inside the home, where soil threatens to make a mess.

Coconut coir is easier to vacuum up than soil, and the bricks are much easier to transport than heavy-duty bags of soil.

Furthermore, coir makes a great mix if you are looking for a soilless medium that retains water better and adds structure to the media.

If you are currently growing microgreens, what mix are you having success with?

Let me know in the comments below!