How to Cover Crop with Fava Beans (Bell Beans) to Make Free Fertilizer

Step inside my garden and rarely will you see a garden bed left empty for more than a few weeks, even when all my plants are done for the season. When soil is bare and untended during the winter months, it can lead to depleted nutrients, compacted soil, and tenacious weeds that pop up at the earliest signs of spring.

That’s why I’m a fan of using cover crops to protect the soil and improve fertility over winter, particularly edible cover crops like fava beans and bell beans.

Read more: More of my favorite edible cover crops that build your soil while they grow

These cold-hardy plants easily survive temperatures of 15°F to 20°F. They’re not as hardy as Austrian winter peas (another excellent cover crop), but are pretty close and can be grown in most climates. They even love the snow and will grow right through it!

Fava beans and bell beans are easy-to-grow legume cover crops that fix nitrogen in the soil—that is, they add significantly more nitrogen to the soil than they use for their own growth. Once they start blooming, they’re cut down to the ground so other plants can take advantage of their stored nitrogen.

Other than that, fava beans and bell beans are essentially the same plant. They both have edible leaves and flowers that taste faintly bean-like and are best used fresh in salads, sandwiches, and creative pestos.

You see, there’s plenty of nitrogen to go around—about 80 percent of the atmosphere is free nitrogen, but it floats around in a form that plants can’t use.

Enter legumes like fava beans and bell beans: They’re unique in their ability to form a symbiotic relationship with harmless soil bacteria called Rhizobia. The legumes provide food (sugars and other nutrients) that sustain the Rhizobia. In return, the Rhizobia pull nitrogen gas out of the air and convert it into ammonium compounds that plants can consume.

Fava and bell beans store nitrogen in small white sacs on their roots called root nodules. When the plants are cut down—and more importantly, when the roots are left underground to decompose—the root nodules release the stored nitrogen for other plants to use.

That means when you plant your next crop, you can reduce (or even skip) the initial fertilizer application because those plants will already be off to a great start.

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Fava and bell beans start flowering anywhere from 90 to 200 days after a fall sowing. This timing is ideal for planting heavy feeders like brassicas (broccoli, cabbage, kale, cauliflower) right after you turn the cover crop into the soil.

Spring planting: In harsher winter climates, you can sow fava and bell beans as a cover crop in late winter to early spring as soon as the soil is workable. I’ve found that they’re more tolerant to heat than Austrian winter peas, so they’ll happily grow into summer when peas generally start struggling.

Fava and bell bean plants typically start flowering about 40 to 60 days after a spring sowing. Timing-wise, that means a spring-sown crop should be turned into the soil between May and June, so think about how this affects your planting schedule.

Though it isn’t strictly necessary, you can also soak bean seeds for a few hours to speed up germination. This is especially helpful if the weather is still dry when you plant and you want the seeds to germinate quickly.

But when I plant a cover crop that doesn’t mind growing more densely, I prefer to broadcast the seeds over my garden bed and rake them into the soil about 1 inch deep. It’s okay if some seeds aren’t fully buried; as long as they stay moist, they’ll germinate.

In dry climates or very cold climates, adding a layer of straw mulch on top will help hold moisture between watering sessions and protect the soil over winter.

If you sowed seeds in fall, keep in mind that plant growth will slow down significantly in winter. But as long your average lows stay above 15°F to 20°F, your cover crop will overwinter and resume growing in late winter to early spring once the days get longer.

They’re well suited for those conical wire tomato cages that, ironically, don’t do a super job of supporting indeterminate tomato plants. But they’re fantastic for fava and bell beans!

So watch for your crop to bloom and get ready to “turn it into the soil,” as they say in gardening parlance.

Traditionally, you would turn a cover crop into the soil by tilling, digging, or forking the plant material under the soil. But if you’re a no-till type of gardener, the “chop and drop” method is what I personally prefer: simply chop the plants down and spread them across the bed.

Then wait about three to six weeks before planting your next crop. I generally recommend this because as your cover crop decomposes, some of the nitrogen in the soil will be temporarily locked up. After a few weeks, the decaying roots will release their nitrogen stores and the foliage will break down into mulch and nutrients for your next crop.

When you’re ready to plant, just push the stems and leaves aside, make your holes, and plant your seedlings. If you want to sow seeds, cover the decomposing foliage with a 2-inch layer of soil or compost (or a half-and-half blend) so you have a clean planting medium for your seeds.

But that’s a myth: Living legumes use most of their fixed nitrogen to grow their own leaves, stems, and flowers. They store the rest of their nitrogen in root nodules until that nitrogen is needed for seed production.

To actually get that nitrogen, you have to chop the plants down (before they set seed) and let the roots decompose in the soil instead of pulling them out. As the root nodules break down over a few weeks, they release the stored nitrogen for the next round of plants that go in.

This post updated from an article that originally appeared on October 15, 2013.