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After your microgreens are cut, what do you do with the spent (harvested) tray? The leftover roots, stems, and growing media can be used to augment your growing or homesteading efforts in a number of ways.
In some areas, you must have a license to compost and reuse growing media on your farm. However, you can still generate worm castings to feed outdoor plants and use the residual root mats and plant matter in other ways.
Nasturtiums, borage, and chrysanthemums greens can be planted directly into garden beds or grow bags and allowed to grow. They produce flowers quickly and can provide an additional product for sale. A 1020 tray of nasturtiums planted in a larger pot can start producing flowers in as little as 4 weeks.
Radish and bok choy trays planted in the garden will produce full-size veggies in 4-6 weeks.
Much like straw, the thick root mats generated by microgreens help the soil underneath retain moisture and nutrients when used as mulch. The presence of decaying roots and the protected soil surface draw worms and beneficial microbes upward.
This reduces irrigation needs while providing some of the benefits of companion planting. For example, pumpkin plants mulched with leftover radish micros will receive protection from squash beetles. They also work great in SFG beds to suppress weeds and protect soil between plantings.
One of the best uses of spent trays is to feed them to your worms. You can remove the spent media from trays to be layered with cardboard or crumpled unbleached paper in a worm bin. The worms make short work of the roots and stems generating usable castings in a few weeks time.
If you raise poultry or ruminates; spent media and residuals can be pulled from the trays and placed out for animal access. Mamas and chicks kept penned for protection particularly like the fresh food and scratching opportunity.
Trays used as living mulch can be allowed to grow until they bolt and produce seeds. The limited space allowed each plant stresses the plant and encourages fast bolting. It is best that this be used by home seed savers as there are regulations in place for the production of seeds used for crops in agriculture. Some great resources on seed saving can be found here: