January 01, 2023 8 min read 0 Comments
The ideal growing medium for microgreens can be different depending on the growing style that you plan to be using. Growers will often use soil, coco coir, hemp mats, soilless mixes, peat moss or some mix of these.
The best medium for growing microgreens is one that allows proper drainage, is sterile (meaning it contains no seeds) and holds moisture efficiently.
It can also depend on your purpose in growing microgreens, whether for personal use or for sale, the best growing medium for you will be influenced by your end goals. Every grower develops their own “best growing medium” recipe, but below we have listed our top 5 choices and the reasons behind them.
Whether you will be growing just a few shallow microgreen trays on a countertop or plan on installing an automated flood and drain rack system, one of these choices will work for you.
The best media for growing microgreens is one that balances good drainage, proper water retention, and nutrition. The preferred growing medium of many of the staff here at Bootstrap Farmer is a mix of 50% coco coir and 50% good organic potting soil. This blend retains water but is kept fluffy by the coco coir. It provides nutrients for longer grows but doesn’t overwhelm the more fragile greens.
Luckily growers in most locales can find a locally sourced potting soil with a nice balance of ingredients that will mix well with coconut coir. Potting soil on its own often holds too much moisture and can lead to mold issues. Adding the coconut coir allows you to stack and compress your trays without the soil mix becoming compacted. If you will be going this route and plan to feed your harvested trays to poultry or livestock, try to find a potting soil that uses decomposed granite in place of the more common pearlite.
Potting soil has the benefit of usually containing a mild fertilizer mix that provides your microgreens with everything they need if the growth time extends beyond the nutrients available within the seed.
Depending on the soil blend that you buy it may retain too much moisture or contain a little too much fertilizer for ideal microgreen growing. This is when mixing in a little soilless media can help balance the growing environment.
Many of the soilless media listed in our next category can be used to lighten up heavier potting soils. Some are more sustainable than others. Your plan for reusing or disposing of your growing medium will help in informing the right choice for your mix. This article on Reusing Spent Microgreen Trays may help you to make your choice. Keep in mind if you will be feeding harvested trays to livestock that it is best to stick with natural materials that are not dangerous if consumed.
Every grower we know has experimented with different growing media for their microgreens. Many of us have found that a mix of ingredients gives us the ideal drainage to be able to water once a day while still maintaining proper drainage and nutrition levels for growing microgreens. Mixing coco coir with a good organic potting soil makes a nice balance.
There are a number of nationally available potting soil brands that will work well for creating your own growing mix. If you have a local soil supplier that makes their own potting mix give it a try. Look for one with a balance of mild nutrients and good drainage.
You can try out different proportions of pre blended potting soil and soilless media like coco coir to find the ideal mix. Starting with 50/50 is a good jumping off point for finding the best balance between proper moisture levels and nutrient levels.
If you find that your soil is not needing water at least every 24 hours, increase the proportion of coco coir. If your soil is drying out too quickly you can increase the proportion of potting soil if your soil of choice has higher water retention level.
Coco coir, peat moss, vermiculite, decomposed granite and perlite can all be useful ingredients to include in a soilless mix when it comes to hydroponic growing. There are pluses and minuses to each one and they require slightly different treatments to perform ideally. None of these growing mediums contain nutrients. For longer grows adding a light, mild nutrient blend will help you get the most out of your microgreens.
For ingredients that are not sustainable we recommend using them sparingly when possible.
Pro-Mix is a pre blended combination of many of the soilless ingredients that are used for hydroponic growing. It is optimized for proper moisture levels for germination and early growth. We like the Pro-Mix HP formulation for growing microgreens. It has a relatively consistent particle size and is pH balanced for a neutral base. This blend also containsmycorrhizae - endomycorrhizal fungi that can help to create a good rooting environment for your microgreens.
Hemp mats are a fantastic choice for growers who are looking for a clean and soilless hydroponic growing medium. Because hemp is sustainable, biodegradable and compostable, it is a great choice for the environment as well. Pre cut hemp mats fit your 1020 growing trays, or can be cut to fit smaller to fit 5 x 5 shallow trays.
Hemp mats are not reusable for growing a second set of microgreens but used growing mats can be put to work in other ways. They make an excellent living mulch to place around and under perennials outdoors.
Coco coir is made from the inner husk of coconuts that would otherwise be considered a waste product. Although there are some environmental issues with the processing of the coir it is one of the most sustainable and renewable choices for hydroponic growing. Coconut coir is naturally fluffy and allows for great root growth.
If you are set on using a soilless growing medium, coconut coir is the best base to start with. Because coconut coir on its own can lock up some nutrients, most notably calcium, it is best when mixed with other ingredients or with a nutrient solution that contains a good balance of nutrients. Many growers who use coco coir exclusively will supplement their nutrient solution with Cal-Mag to circumvent this problem.
Pro-Mix is a good choice for microgreen growing because it is a reliable product that is generally available nationwide. Most hydroponics stores will carry Pro-Mix or a similar product that is sterile and soilless. When you are just starting out with microgreen growing, using a ready made growing media mix can help you to focus on the other aspects of learning to grow.
Many experienced growers choose to use a ready made mix as well for consistency. While not as big of a problem for the home grower, a change in growing medium constituents can cause problems in the grow room. You may need to adjust your watering schedule, find your greens more susceptible to mold growth, or see decreased germination rates when changing growing media ingredients.
Coco coir is a fine growing medium for microgreens when used on its own. Because it doesn’t contain any nutrients, longer grows may require an addition of a light nutrient solution to the watering regime. It is also a fantastic ingredient for adding to your own mix. It is fluffy and light, holds water well and has a neutral pH.
Coco coir can be purchased locally from many garden supply or hydroponic stores. It is also available compressed into coco bricks which expand greatly when rehydrated. Warm water will speed the rehydration process and a single brick weighing just over a pound becomes enough coir to fill three 1020 shallow microgreen trays.
Fabric mats made from hemp fiber are a fantastic, mess-free option for microgreens growers. This sustainable option is compostable and easy to use. What is really great about this option, is it is a pH neutral medium. Jute mats are also an option for growing microgreens. The finer the weave the easier it is to hold small seeds in place.
Metal screens seem to be the latest fad in microgreen growing. While the idea of having a constantly reusable growing medium is attractive for many reasons, we have yet to be convinced of their value. They can be difficult to clean but if they work for you, good luck.
Microgreens should be grown in a sterile, growing medium that is easily drained and that holds moisture. Any of the choices above can work great for growing your microgreens. We recommend trying a few different growing mediums and finding the one that works best for your style and your growing space.
The best growing mediums will have you watering once or twice in a day depending on temperature and ambient humidity. If you are unsure How to Water Microgreens check out this article for help with methods.
After you decide which type of microgreen growing medium to use, it is time to choose your microgreen seed varieties. We always recommend starting out with the easier varieties like broccoli and radish. If you have further questions about learning to grow microgreens at home, lighting options and troubleshooting mold problems, check out the articles in our Microgreens Growing Guide blog.
If you are getting ready to start a microgreen business or are ready to start with some of the more difficult varieties our Ultimate Microgreens Growing Guide has more in depth information. Also check out this microgreens farm tour to get inspiration from a larger scale operation.
Be sure to share your microgreens growing successes with us on Instagram and tag us with questions you have about the process.
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