Written By Lara Wadsworth

Microgreens are gaining popularity among growers and consumers. They are nutrient-dense, easy to produce, and can turn a profit quickly. The rising demand for efficient growing mediums continues to propel researchers to find better options beyond soil or hydroponic systems. Growing mediums may not seem like a big deal when it comes to microgreens, but studies are finding that they can have a significant impact on root health, nutrient uptake, and yield, among other things. Two studies published in 2024 have proven that coco coir (AKA cocopeat) and vermiculite are the top two growing mediums available for many reasons.

What Makes an Ideal Microgreen Growing Medium?

Microgreens are easy to grow, yes, but they can be a bit picky. When it comes to where they will grow, we need to consider things such as water retention, aeration, nutrient support, sustainability, and cost. The most traditional mediums were soil, peat moss, and synthetic mats. All of these options are usable, but they all have significant disadvantages for one reason or another. Soil may seem like the obvious choice, but it often harbors pathogens, produces inconsistent results, and can be messy to work with indoors. Cococoir and vermiculite are not only better for yields and nutrient density of microgreens, but they are also significantly easier on our global supply chain, making them the overall more sustainable options.

Coco Coir: A Natural Powerhouse

Coconut coir is the leading replacement for peatmoss in the horticultural world. While peat can only be harvested by harming a specific endangered environment, coco coir is a natural byproduct of coconuts that was previously being thrown out. If appropriately processed, it is a fantastic option for microgreen growers. Coco coir is a renewable, biodegradable material that is widely available in various forms, making it easy to use for anyone.

This fine-textured growing medium is soil-like and has excellent water-holding capacity while maintaining good aeration, both of which are crucial for healthy roots. A study published in Food Chemistry: X “showed that the cocopeat growing medium was the most effective growing medium for the cultivation of microgreens to increase microgreens plant growth, yield, nutritional, biochemical composition, and antioxidant activity of microgreens.”

The biggest downside of coco coir is that it needs to be adequately processed and have any excess salts washed out of it. Luckily, True Leaf Market triple-washes their coir to ensure the best growing conditions. There is no need to worry about quality here. Cocopeat is also pH-neutral to slightly acidic, perfect for growing microgreens! It also has a limited nutrient content. While this is a downside for growing other plants, it is actually beneficial for growing microgreens, as they can easily get burned from too much nutrient content at this early stage of growth. It is easy to control exactly how many nutrients are in the medium with supplemental feeding when necessary.

Vermiculite: The Lightweight Mineral Medium

Vermiculite is a naturally occurring mineral that, when heated to expansion, turns into lightweight, porous granules. It has been used in the horticultural industry for years as a potting soil amendment to help get the perfect balance of water retention and soil aeration. It has just recently been discovered as a great option for microgreen growers. It is sterile, inert, and entirely safe for growing food. It also has excellent moisture retention and promotes uniform seed germination. It provides aeration while preventing compaction and can be blended with other mediums (like coco coir) when desired.

The biggest downside of vermiculite is that it has less structure when compared to coco coir and therefore may not support larger root systems of larger microgreens long-term. Yet, there is no need to worry about how the vermiculite was processed. This 2024 study concluded that “vermiculite increased the yield [of microgreens] by 10-18 [percent] compared to the peat-based medium,” and “microgreens grown in vermiculite had a significantly improved plant height, hypocotyl length, stem diameter, single-plant weight, and yield.” For best results, vermiculite can be mixed with coco coir to improve soil aeration and water retention further.

Beyond plant health and yields, coco coir and vermiculite remain top of the pack. As mentioned above, peat harvesting damages fragile ecosystems, and traditional synthetic mats rely on fossil-fuel-based inputs to produce the medium. In contrast, coconut coir gives a second life to products that were previously getting discarded as useless waste, and vermiculite is abundant, inert, and leaves a light environmental footprint. Choosing these mediums means supporting a brighter future for our earth and a more resilient and sustainable supply chain without compromising performance.

Coco Coir and Vermiculite: The Power Couple

The answer is that coco coir is best for beginners, but the best solution is to mix coco coir with vermiculite for optimized aeration and water retention. Remember, always pre-moisten the medium before sowing microgreens. Use clean trays and fresh, sterile medium to avoid contamination or mold growth. Also, never underestimate the benefits of high-quality seeds when growing microgreens!

These studies have proven that the growing medium you choose not only impacts yield but also the nutritional profile of the final product. Vermiculite, for example, was associated with higher iron levels in broccoli microgreens, while coco coir cultivation improved antioxidant activity and overall nutrient density. This means those using these mediums are producing not only more microgreens, but microgreens with better health benefits.

• Emergence of microgreens as a valuable food, current understanding of their market and consumer perception: A review
• The Performance of Growing-Media-Shaped Microgreens: The Growth, Yield, and Nutrient Profiles of Broccoli, Red Beet, and Black Radish

Both coco coir and vermiculite stand out as reliable, effective mediums for microgreens. The increasing mass of scientific evidence strongly supporting coco coir as the superior medium for yield and nutrition is hard to ignore. And, vermiculite adds undeniable value in the mix. For growers seeking consistent results, coco coir and vermiculite are proven, sustainable choices to improve microgreen yields in the short and long term.

Lara Wadsworth, True Leaf Market Writer

I am a native of Southwestern Michigan, where I currently reside. I love all things plants! After completing a Bachelor's Degree in Horticulture, I found a dream work-from-home job that allows me to share my passion. Now, I spend my days writing for TLM, playing with my dog, eating delicious food with my husband, and plotting my next landscape or gardening move. I believe everyone should get down and dirty in the soil now and then. Happy Gardening!