Friday, September 16, 2011

Green Manuring By Grace Olson

    Once when I was in early high school my mother asked me to take my old Toyota pickup and drive to a local dairy farmer to buy some manure for her garden. I dutifully chugged over to the quiet farm, where the owner’s teenage son helped me load several tractor buckets full of fresh, steaming slop into my truck bed. I puttered on home and began shoveling it out onto her beautifully maintained plot, eyes watering with the stench and wondering how anyone could stand using the stuff. A half-hour later, my mother came home, took one breath of the chaos ensuing in her yard, and explained to me in some very heated language all about the term “composted.” In the end, her garden recovered and we now laugh about how that was some really “green manure.”

    Fortunately, the term’s actual meaning is far more beneficial to the Front Range home gardener. In effect, using a green manure means growing your own fertilizer and compost. You take a cover crop, usually a grass or legume seed broadcast over a soil surface, let it grow a while, and then till it under a month or so before planting your garden. The tilled-in plant material adds fertility and soil structure to your garden plot. For most of Jefferson County, mid-September is the perfect time to begin a fall-planted cover crop for spring till.
Hairy Vetch

    Choose a rye/hairy vetch or rye/Austrian winter pea mix so the crop will overwinter in Colorado. Mix with a rhizobium listed on the bag and broadcast over your garden. (Rates can be found in Table 3 of Garden Notes 244, click here). You may choose to cover the seed with bird netting or less than one inch of straw to ensure germination, and water often to keep the soil slightly moist until the crop is established.

    The seed will grow all winter while you feast on last season’s harvest, sip hot tea by the fire, and order new seeds for the spring’s planting. 

    One month before you plan to fill the area with your vegetables or flowers, till the cover crop under, thereby turning it into your very own green manure. You can get a motorized tiller or use a spade, depending on the size of your garden. Waiting one month allows the plant material to decompose properly before your seedlings enter and compete for soil oxygen. Its nitrogen is released into the soil and its slime, mucus and fungal mycelia glue soil particles together to improve the tilth.

    Whether you are wrapping up your harvest and can afford the space to cover your entire garden plot, or you wish to fill the area left by your broccoli or tomatoes, a green manure crop will benefit your garden. And, even if you ask your inexperienced teenager to help you, there is a lot less room for error than that other kind.

    For more information, read Colorado State University Extension’s Garden Notes 244.