Choosing a good growing medium in microgreen production is one of the major aspects to think about and establish. When I ventured into growing microgreens, I was amazed that I can start with just a few materials. There are a bunch of options for growing mediums, but which one is best for microgreens?
In general, the best growing mediums for microgreens have high water retention and small particle size. The most recommended are 1) coco coir, 2) paper towel, 3) water, 4) hydroponic mat, and 5) vermiculite. Potting mixes are also used with a 4:1 ratio of organic to mineral substrates.
What is the most accessible? Are there growing mediums for microgreens that are organic? Which is the easiest to use? These are concerns I asked myself back then. Today, we will answer this one by one. So let us dive in!
Coco coir is an easy-to-use growing medium that can support microgreens well. It has high water-holding capacity and porosity which are essential for good microgreen growth.
If you are a newbie gardener, this option might be the best for you! One of the best things I like about coco coir is that it is really beginner-friendly.
First, because it looks and acts like regular soil! With its appearance, a beginner would be more comfortable with the idea of using it—unlike using clay pebbles or gravel as a growing medium. To use it, you just need to put the coco coir in a container, place your microgreen seeds, mist them, and you are good to go!
Second, coco coir also has promising characteristics that are beneficial to your microgreens! It is lightweight, giving your microgreens plenty of space for proper air and water circulation for optimal root structure. Coco coir is not too firm and not too loose to use. Furthermore, it can even retain a lot of water and oxygen!
Lastly, since it is made from the outer husks of coconuts, coco coir is an organic growing medium! Who doesn’t like that? With this, growing your own food in your kitchen can be done 100% organic—no artificial fertilizers, no synthetic chemicals!
Paper towels are the cheapest growing medium for cultivating microgreens. There are only 2 necessary requirements for growing microgreens in paper towels, water and sunlight.
You might be surprised, but yes! You can absolutely grow on paper towels! You might be wondering, why? Let us have a review about microgreens.
Remember that microgreens can be harvested as early as 5 to 7 days, depending on the plant. Some plants, like broccoli, for example, will sprout as early as 2 to 3 days and they can be ready for harvest after 1 week!
Considering this short timeframe, they have few growing requirements. They just need water and sunlight. Adding nutrients can also be a bonus step, but not that necessary. Thus, it is possible to cost-effectively grow microgreens in paper towels because of these few growing requirements.
Water is an effective growing medium for microgreens, but it must be paired with the right microgreen growing tray.
I know what you are thinking. You may be asking at this point: Really? Just water?
Let me answer, yes. Just. Water.
However, you need a microgreen growing tray with a water reservoir below. The one below is the microgreen growing tray I have been using ever since.
You can notice that it has two trays. The white tray is where you can put your seeds, while the green tray is where you can pour the water.
During the first 2 days, you still need to mist the seeds with water. When you observe short roots developing, it is time to pour water into the green tray. But, you do not need to fill the green tray way to the top. Just maintain a water level such that the tips of the roots are touching the water.
When the roots of your plant have access to the water, they will grow well. See? Easy as that!
Hydroponic mats hold microgreens well and absorb water excellently. They are made from natural fibers such as coconut, hemp, jute, among others..
This is also an easy-to-use option! If you already have a tray, you only need to fit the hydroponic mat with the tray size and cut it. It is as easy as cutting a piece of paper!
After that, you can already place the seeds above the mat, mist, and they should be good after a few days.
Vermiculite is a non-toxic and sterile option for growing microgreens. Its excellent water retention and capillary action properties allow the microgreens to be fully hydrated by applying water from above and below the roots.
To explain capillary action, let me give a real-life example. Have you ever noticed your drink staying inside your straw? The force that your drink exerts to fight the gravity, that’s supposed to pull it downwards, is capillary action.
This property is essential in growing microgreens because the longer time water is in the growing medium, the longer water access there is for your microgreens.
Vermiculite is a prominent growing medium because of its cheap price. Packs like this are available on Amazon.
To use this growing medium, you just need to spread it evenly on your microgreen growing tray, place your seeds, cover them with a thin layer of vermiculite, and mist, and then you are good to go.
Most of the time, vermiculite is mixed with other growing mediums for better performance. You will know more about these mixes in the next section!
When mixing different growing mediums, the ratio of organic material to mineral substrates should be 4:1. Organic materials such as coco coir, sterilized compost, or peat moss can be mixed with either vermiculite or perlite. Mixing is done to balance the water holding capacity and air space in the medium.
Other combinations that might work for you are 60% vermicast mixed with 40% carbonated rice hull; 50% garden soil mixed with 50% coco coir; and 50% carbonized rice hull mixed with 50% coco coir.
Growing mediums with large particle sizes, such as clay pebbles, gravel, and rockwool, are not ideal for growing microgreens.
Due to the low water holding capacity of clay pebbles, they are not ideal for growing microgreens. Clay pebbles are more compatible with tall, full-grown plants such as eggplant, tomatoes, and peppers.
Clay pebbles, also known as hydrotons, have a big particle size of 4-25 mm. When we say particle size, it is the size of each known particle.
To give you a clearer illustration, look at your thumb. Individual clay pebble particles are at least ⅓ of your thumb! So imagine growing a bunch of microgreens in those big particles. Clearly, they cannot support microgreen growth because the roots cannot grow into them.
Another issue for clay pebbles is their low water holding capacity. As I mentioned at the start of this article, microgreens only need a few requirements. Water is one of those.
Since clay pebbles cannot hold a sufficient amount of water long enough, it may not sustain and provide the water needs of the microgreens.
This growing medium is more compatible with hydroponic systems such as deep water culture.
Learn more about this system in our article on deep water culture.
Gravel, like clay pebbles, have low water holding capacity and is not recommended as a growing medium for microgreens.
Same with clay pebbles, gravel has a relatively large particle size, compared to the ideal growing mediums for microgreens such as coco coir and other potting mixes. For this reason, using gravel is not ideal.
But did you know that we have several options for growing mediums?
Learn more about them in our article on how to choose growing mediums.
Rockwool can only hold small bunches of microgreens, which is not ideal since microgreens are planted in dense amounts.
One of the unique characteristics of microgreens is their dense planting method. You can just spread thousands of seeds in a simple tray, and wait for them to grow.
So if you use rockwool, which can only accommodate 2 to 3 seeds per piece, then you will have very few harvests!
Can you reuse hydroponic mats after growing microgreens?
Yes, hydroponic mats can be reused. Hydroponic mats can be dried out to be used again. But, if the mat is already dominated by roots, it is best to turn it into compost. However, if molds develop during the first use, it is not recommended to use that hydroponic mat again.
What do you do with organic growing mediums after growing microgreens?
Used organic growing mediums can be turned into compost. After harvesting the microgreens, put the growing medium into a bin with soil in the bottom. Afterward, cover it once again with a layer of soil. Set the bin aside for 12 days, or until the roots have completely broken down. Mix the compost well and use it in the garden.
Coco coir, paper towel, water, hydroponic mat, and vermiculite are five of the best growing mediums for microgreens. They perform better with microgreens because of their small particle sizes, ease of use, water retention capacities, and capillary action mechanisms.
Potting mixes are also a prominent choice for microgreen gardening. A ratio of 4:1 is the ideal combination for organic materials like coco coir and mineral substrates like vermiculite respectively.
In contrast, clay pebbles, gravel, and rockwool are not recommended to use as growing mediums for microgreens. This is because they have large particle sizes, low water retention capacity, and are not compatible with the dense growth of microgreens.