How to dispose of the leftover Grow Medium after harvesting Microgreens

One the main questions that we receive through our YouTube channel, Website and Social Media is “What are you supposed to do with the leftovers from harvested microgreen trays?”. There are a lot of options out there and it really comes down to how you want to handle it! However, we did our best to break some of them down for you.

First, it depends on what type of grow medium you are using. If you are using soil, coco-coir, or hydroponic grow mats like hemp, you can toss those into your home compost bin, and they will break down over time. Then once the used microgreen mat has broken down completely, we will reuse ours in our outdoor garden beds like this picture to the left! There are some grow mediums which require special treatment for composting, such as Biostrate which requires you to take it to Industrial Composting Facilities to be broken down. Biostrate simply will not breakdown in a normal backyard compost.

Let’s talk about what we do here at On The Grow with our leftovers... When we use a Microgreens grow medium that is able to be composted (coco-coir, soil, etc.), We like to remove the “Root Mat” from the microgreens tray, then we toss it to our Compost bin. Over time, the Root Mat will be broken down by organisms and microorganisms until there is only “finished product” ready to be used! Once everything is broken down and ready for use (2-10 months), we stick to using it in our outdoor garden only... Notice we say “garden only”, that is because there is a higher chance of a pathogen being present in the composted grow medium and we prefer really clean medium for micros. 

Another option you have if you don’t own a Compost bin is to simply toss the “Root Mat” somewhere in your yard and send it back to the earth by mowing over it… or simply let it do its thing, haha. This is a lazy method and can make your yard look weird, but we are completely guilty of doing this in the past...

Funny enough, we created a Permaculture area in our yard by accident from the left-over Microgreen seeds germinating late and ended up growing into adult plants. Personally, we thought it was pretty neat and so did the bees that were drawn to our yard. Since we bought our own house, we purchased a new compost bin called the GeoBin and it has been amazing to us so far. The process of setting it up was extremely quick and easy, and we will definitely recommend it if you have a lot of Microgreen leftovers to compost. Otherwise, there are many other great options out there for composting solutions so look around and see what works best for you and your needs!

What do you do if your using a reusable medium?

When using a reusable grow medium, you want to try and remove the left-over microgreens & roots. If you're using a mesh screen, then you simply remove the harvested Microgreens leftovers and compost them afterwards. You can do this by pulling them out or scraping the remains into a compost bucket with your hands.

Use caution not to damage the reusable grow medium and remove as much organic material as possible. Rinse the mesh screen and give it a quick sterilization with H2O2 or other sterilizing solution. A fine-mist bottle works best for covering the entire reusable grow medium. Another option for sterilizing the reusable medium is dunking it in a sterilizing solution. Click here to view our Blog On Sanitation or here to watch.

If you are using grow mediums like Perlite, Coco coir, Vermiculite…etc. then there is a whole process to safely reusing the grow medium that can be more time consuming. First, you would want to do your best to separate and remove as much of the microgreen & root debris as you can from the grow medium and toss the organic materials into your compost bin. To separate the organic material from the grow medium, you can use some kind of mesh screen that allows the medium to fall through but catches the roots/stems and other organic material. Then you will need to sterilize the grow medium by baking it in the oven. Online it says to do this process: put some grow medium (about 4 inches deep) in an oven-safe container, like a glass or metal baking pan, cover with foil. Place an oven-safe meat thermometer into the center and bake at 180-200 F. (82-93 C.) for at least 30 minutes, or when the soil temp reaches 180F.

Note- Any temperatures higher than 180F can cause the medium to produce toxins.

After doing those two steps, you would let it cool down and then the grow medium can be reused. But keep in mind, there could still be potential for pathogens, and you should use this process with caution. We don't like this method, but we've heard some people have great results with it. Please use caution when attempting to bake your medium and research the best/safest method for sterilizing your medium.

Final options

Personally, we prefer to start each grow with new medium and compost it after each harvest…that way we know our grow medium is clean every time, and we do not have to add additional time to our growing procedures. Plus, we get a ton of great, composted soil for our garden! You can also just toss it in your trash can and say goodbye, but why not allow it to properly breakdown and be reused somehow! It is up to you!

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Written by: Mandi Warbington
Published: August 3, 2020
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