Best cultural practices for microgreens: A quantitative and seasonal analysis

At first, conditions were difficult to control because of inconsistency in the soil mix we had available. Despite our efforts to control conditions within each treatment, low quality soil mix in June especially lowered all yields during a time when they could have been very high. Our first important observation is that consistent availability of affordable, high quality soil mix is imperative. We now have settled on using GreenTree’s AgBlend from Ithaca, NY which is a peat-light blend with coco, earthworm castings, and organic nutrients like greensand, bone char, sulfate of potash, vegetable protein such as peanut meal, and animal protein such as feather meal. Rapid nitrogen availability is important for high yielding microgreens. The nitrogen in many organic soil mixes is often not immediately available during the short 2 week growing period of microgreens, causing yellowing or low yields. We found bottom watering with our aquaponic water or other hydroponic solutions with more available nitrogen was very helpful.

The heating pads sometimes proved a barrier to success. While they certainly seemed to help boost early growth in the first few days after seeding, the benefit of the heat pads was difficult to quantify. The thermostat that came with the heat pads was unreliable, and the way it inserted it into one of the trays for monitoring did not work well. The knob for adjusting the heat was easily knocked by daily working activities. Often, heat pads would over-heat the microgreens soil trays and young germinated plants would dry out, overriding the benefit of the heating pads.

The other ongoing task throughout the season has been to adjust greenhouse conditions as the temperature, humidity, and amount of sun changes outside. Greenhouse doors are open or shut as humidity fluctuates. No extra lighting was used on the microgreen trays, so amount of the amount of light they received varied greatly.

One important adjustment that we made was the irrigation system. Watering by hand became extremely time-consuming once the greenhouse starting getting very warm all day in May, so we set up a hydroponic table that bottom-waters the trays, speeding up the irrigation process and keeping leaves dry (water on leaves encourages mold growth). Ventilation by fans is another very important component in the winter time when greenhouse doors are closed. Because of the aquaponics system especially, the air is very moist,the high humidity encouraged mold and caused crop failures in many trays. Another ongoing project on the farm this year will help facilitate installation of a biochar furnace in the greenhouse, making the air much dryer and potentially affecting microgreens production over the winter when it is running.

In order to correct for some of the variability in our experiment, including growth media quality, heat pad blunders, changing greenhouse conditions, and human error in growing all of these varieties successfully, we chose our highest recorded yield per tray of each variety in each month of the year. These ‘highest yields’ were used to analyze the success of each variety when grown correctly. Starting at the end of November, greenhouse ambient temperatures did not rise above 60F until March. This represents the time period when the colder hardy varieties play a larger role in the microgreens mix..

Our greatest takeaway from this experiment is that microgreens growing can be profitable in 3 seasons with minimal investment. Winter growing is certainly possible, but may require investment in more sophisticated infrastructure (such as heating pads), limiting the mix to only cold-hardy varieties, and the maintenance of reliable markets. In certain years and latitudes more sophisticated greenhouse structures and even supplemental lighting may be necessary to make microgreens a true four-season crop.

The following tables are a breakdown of fixed costs per tray and a summary of our greenhouse air temperature, crop yields, harvest periods, and profitability on a per tray basis. More detail regarding these numbers can be found in the attached data sheet (Microgreens Financial Data Summary) that goes into further detail with this information regarding each variety we tested.

We’ve determined .25 lbs/tray as a yield target indicative of an effective growing system. Higher yields are certainly possible and desired, although excessive weights per tray may indicate greens that are closer to “baby” than to “micro”. Below .25lb/tray micros are still profitable according to our model, however lower yields than this can indicate some issue in the growing environment or quality issue with the greens that should be corrected. Our profitability model is also based upon successful growing. Microgreens can be quite profitable if the grown consistently, however crop failures can happen easily as the seedlings are very delicate and prone to mold and drying out. Low yields in May, noted in the above table, were most likely due to inadequate irrigation--difficult to maintain during constant suny conditions. Successive crop failures can make what might seem profitable a money losing venture. On the bright side, because of the rapid cycle time compared to other crops, the grower can learn quickly and experiment and refine and improve their growing system and technique quickly over the course of a season.

Although some crop failures hindered our microgreens operation in our first year during this experiment, the process allowed us to refine our system, and now our yields are more consistent and the farm is successfully growing and marketing 15-20lbs of microgreens a week through retail and wholesale outlets at $28/lb on average. This is mainly through the Syracuse Regional Farmers Market and to restaurant and small supermarket customers in Central NY.

Our profitability model of microgreens represents an enterprise that uses existing greenhouse or high tunnel space on the farm that is unfilled or under-utilized during certain times of the year. We found that in terms of operating expenses, a tray of microgreens, if yields are fairly consistent, and marketing channels are stable, will provide a good return during the main season, and with the right varieties, break-even in the colder months. Our model does not represent an enterprise that takes into account the capital expenses of a dedicated greenhouse for microgreens. Microgreens can justify such an investment for growers wishing to scale up production; but those costs would likely lead to a smaller profit margin than what is indicated in our model.

Variety selection:

Varieties should be chosen and grown based either on their high yielding quality, for their distinguishable taste (like a spicy mustard), or for the aesthetic value they add to the harvested microgreens mix (like amaranth).

Mizuna, red russian kale, red cabbage, and kohlrabi offered the most consistent yields even in cooler temperatures. Under proper management these varieties seem to have the potential to consistently yield a quarter pound per tray throughout most of the year with some supplemental heat in winter. These varieties are recommended to form the core of a microgreens mix and have the most potential for being a viable four-season crop. Three of these four, Red Russian Kale, Red Cabbage, and Kohlrabi, did not fare as well in June and can be replaced with warm season mustard varieties.

Mustard varieties (Scarlet Frills, Garnet Giant, Southern Giant) are effective during warmer months, but not recommended for cooler season or winter growing. These varieties can be high yielding in warmer months but were not consistent in cooler months in our system. They however add a delicious spicy flavor and are visually appealing. Some season extension is possible but pushing them through the winter is not recommended based on our experiment. They were a welcome addition to the mix during the main growing season from March - October due to their unique flavors.

Amaranth had an even shorter season, March-September. Deep magenta coloring and unique leaf shape made it an important accent to the mix, but it has the most expensive seeds and was not consistent when average Greenhouse temperatures dropped below 65F-70F. It is not recommended for growing from October through February.

Our trays growing without any supplemental heat ceased to be effective when greenhouse air temperature consistently dropped below 60F, mid Nov-February. When it is too cold, harvests either failed or took 3-4 weeks. While profitability is lower, winter growing can still be viable if charging a winter premium at market, sales are still consistent, or maintaining market connections is very important.

Starting at the end of November, greenhouse ambient temperatures did not rise above 60F until March. This represents the time period when only cold hardy varieties should be grown.

• Table 1. Avg Greenhouse Air Temps by Month
• Microgreens Financial Data Summary