Six weeks ago, I churned large quantities of spent grains, a byproduct of beer-making, into the soil in a couple of plots in our community garden in Roxborough. Perhaps it was too late, but only then did I post a question about the advisability of doing so on the Philadelphia Urban Farm Network forum. In short order, I got six thoughtful responses. The respondents were unanimous: I had probably made a mistake. Compost the stuff first, or use it as mulch, most of the respondents advised.
It’s not that I wasn’t forewarned. As I wrote at the time, I had read up on the downsides of using spent grains but proceeded anyway, hoping that the ones I was using, from the nearby Twisted Gingers brewpub, were well enough along in the fermentation process that they would quickly break down in the soil in the several weeks I intended to wait before planting.
I still had reason to hope that would happen but the responses to my query were alarming enough that I scurried back to the garden a couple of days later, shovel in hand, to churn the soil a few more times. It was a good thing I did that before too much time had passed. The spent grains had already started to solidify into layers like sedimentary rock. One of the PUFN responses, from a gardener named Scott, had warned about that. “Unless completely mixed into the soil spent grains will stay clumped for months,” he said.
On that second pass with the shovel, I apparently succeeded in mixing the spent grains in well enough. Within three weeks only traces remained intact. But would the amended soil be seed- and plant-friendly? That was the big question, and the answer was no sure thing. As Scott warned, “Have you checked the pH? Spent grain put directly in soil without composting will lower the pH as it decomposes.” And if the pH falls out the optimal range, “a host of ills may follow,” as an article in Fine Gardening explains. I had also previously read that too many spent grains in the soil could inhibit seedling growth. So it’s a good idea to plant some radishes in the soil to see how they fare before doing any more extensive planting.
So I planted a few radishes. Three weeks later, they are thriving. That’s fortunate because even before the radish test results were in, I planted squash, eggplant, peppers, and tomatoes in another section of the garden that I had heavily spiked with spent grains. They are thriving as well.
Have I proved the skeptics wrong, or did I just get lucky? Who knows. But for anyone who doesn’t want to take the risk I was willing to assume, all authorities agree that spent grains make a great addition to a compost pile, giving the finished product a welcome boost of nitrogen.
“It is not hard to compost,” wrote Karl, in another of the responses to my query on the PUFN forum. “All you need is enough brown material for the spent grains that you have; I’ve had lots of success with clean woodchips and leaves. As long as you layer the greens and browns well, you don’t need to do a lot of turning. You will want to cap the pile with leaves to hold in the moisture and the smells. If you do use woodchips, they will take a good bit of time to break down completely. you can speed up the process by sifting out the woodchips. The sifted woodchips can be added to the next batch of spent grains.”
