Monday, December 17, 2012

Cover crop: fava beans

Illustration and sign for Cover crop: Fava Beans (vicia faba)

I always feel bad when it's time to dig my cover crops in. You're supposed to dig them in just before they flower, so all the stored energy and nutrients go back into the soil instead of into fruits and seeds. Still, it feels wrong to chop down a bunch of healthy plants just as they start to flower. Particularly when, if you left them alone, they'd produce delicious, tender, buttery fava beans.

So I'm trying to reshape my thinking. After all, this is why I planted these seeds — so I could chop them down. Instead of thinking about the fava bean harvest I won't get, I'm trying to think of this as a harvest of nitrogen and other nutrients.

Fava bean (vicia faba) plant

Dried fava beans in shells in a basket

Fava beans and shells being planted

Favas and other nitrogen-fixing cover crops have a relationship with soil-dwelling bacteria. These take otherwise unusable nitrogen from the air and convert it to a form that plants can use. The nitrogen only stays in the soil, though, if the host plant is cut down, chopped up and dug under before it flowers and goes to seed.

Favas also have taproots, which help to pierce and break up the dense clay of the local soil, giving future plantings an easier time of it. Left to rot in place, the fava's decomposing roots will leave tunnels that the next crop's new roots can follow, part of the slow process of turning clay into rich garden soil.

Sure, I could let the favas continue, harvest them, and then add nutrients and humus in another form. Store-bought fertilizer isn't the end of the world. Or I can step back from the the drive to maximize yield, to take as much as possible from the ground. The garden's productivity isn't measured only in terms of how much I can transfer from the soil to my plate.

Come spring, this garden bed will be richer, deeper, and house more worms and bugs and beneficial microfauna because I fertilized it this way instead of another. Giving up this crop of potential beans means that the next crop I plant in this bed will grow stronger and healthier.    

Fava bean (vicia faba) flower
Vicia faba, fava beans