Compost Tea … If it’s Good Enough for Harvard

Dylan Reilly works for Solar Mowing. He’s applied to the Landscape Architecture Graduate Program at the University of Maryland for the fall. 

The idea to make compost tea has been on a back burner, so to speak, since I read about Harvard University’s transition to organic care of the Harvard Yard. This time-honored landscape includes brick pathways, stately old trees, and a good deal of grass.

It began in 2008 when Harvard compared two plots of lawn: one treated organically and the other treated conventionally as a control. Both plots were tested for percolation, pH, and other metrics to assure a fair comparison. The conventional control plot received synthetic nitrogen/phosphorus liquid fertilizers, some pesticides, and annual aeration/reseeding. The organic plot received aeration, reseeding, topdressing of compost, pelletized organic fertilizer, and a special amendment called compost tea.

Compost tea is a mix of organic nutrients (nitrogen, potassium), actively aerated water (by oxygen pump), and compost (such as chicken manure, grass clippings, decomposing leaves) that steep together in a fine mesh bag that allow microbes, but not soil, to pass through. Harvard’s recipe mixed seven pounds of compost, eight ounces of molasses, eight ounces of liquid kelp, eight ounces of fish hydrolysate, and a half cup of vegetable oil into a 30-gallon container of water that was then steeped for 24 hours.

The heart of compost tea is not the nutrients from the various ingredients, but rather the biology that is harbored by the steeping process. This is where the aeration comes in. To create beneficial microbes for a healthy lawn you need food to help beneficial bacteria from the compost grow and air to help them breath and that is exactly what brewing/steeping compost tea does. Once brewed, it should be applied as quickly as possible to take advantage of that biology.

Dylan sets the compost tea bag in place and fires up the hydroponic oxygen pump. He'll apply about three gallons of compost tea to his lawn.

Dylan sets the compost tea bag in place and fires up the oxygen pump. He’ll apply about three gallons of compost tea to his lawn.

In my experiment, I applied about three gallons of compost tea to our one-eighth-acre of grass, which is actually more than recommended. About a month later, I have not noticed any particular uptick or decline in our lawn’s growth or health, which is not surprising for one application. But the brewing was definitely an education. I used a 30-gallon trash bin to brew my tea, along with a store-bought 400-micron teabag, oxygen pump, and homemade aeration grate for the bottom of the bin. I dispensed the tea with a one-gallon hand sprayer.

In February 2009, Harvard put out a report on the project, detailing successes from the organic lawn care system, such as increased root depth and less required watering. A few months later, 25 acres of Harvard’s campus was converted to organic practices. With a 45K investment in composting facilities, compost tea brewers, and associated equipment the cost of the new maintenance plan is about the same as their conventional system.

The take-away for folks with lawns is this: It has never been a better time to start an organic lawn care regimen. Compost tea has become a bit of a waving flag in the past few years, but it really appears to be the synergy of compost topdressing, aeration, reseeding, organic pelletized fertilizer, compost tea, and careful management that allowed Harvard Yard to go green.

Comments

  1. So where did you buy your supplies? I tried one application this year also, but didn’t see much either. What else would you recommend as a total organic regimen for this area?

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