Fava beans are self-pollinating annuals, and their seeds are viable for 2 years. Cold-weather fava beans, such as Banner, can live at temperatures as low as 10°F.
Fava beans are classified as ‘heavy givers’, which means they bring large amounts of nitrogen into the soil.
Fava beans are exceptionally good for green manuring if you plan to plant tomatoes; their decomposed bodies help eradicate tomato wilt organisms from the soil.
Directions for cover cropping with fava beans:
- If starting indoors (recommended): 7-8 weeks before first frost (Redding, CA = 9/16-9/23) start 9.1 oz of fava beans, per 100 sq ft (this is about 457 seeds). Transplant them when the seedlings are 1″ tall and the roots are about 1-2″ long.
- If directly sown, 6 weeks before first frost (Redding, CA = 9/30) sow beans on 8″ centers (for 100 sq ft this is 6.4 oz or 320 seeds), covering with a thin layer of soil
- Cut down the fava bean plants anytime after 10% of them have started to flower, but definitely before they get to over 50% in flower. When they start to form seed, they use up the nitrogen that they have stored up in their root nodules. If they get to 50% flower before February 1, then just knock them back to about 6″ above the soil and let them grow again, otherwise knock them back to the ground at 2-3 weeks before it’s time to plant the main crop.
- The cuttings can be moved to the compost pile or, to compost in place, spray with fish emulsion and turn under
- Just before planting the main crop, sprinkle with 1/2 to 1″ of completed compost, then work it into the top 2-4″ of soil.
Cold-weather fava beans, interplanted with a winter grain, such as wheat or cereal rye, cut down when the legumes are at 10-50% flower, can contribute about half of the total nitrogen needs for that year. A minimum of 0.5 lbs of nitrogen is needed per 100 sq ft. The other half of the nitrogen needs can come from compost.
Another good cover crop mix is wheat, cereal rye, fava beans, and vetch. Wheat & rye have extensive roots that improve soil structure, while fava beans and vetch add lots of nitrogen (as long as it’s cut down before over 50% flower), and the grains and fava beans act as supports for the vetch, which sews them all together to withstand wind, rain, or snow. Ratios for the mix to cover 100 sq ft:
- 2.0 oz hard red spring wheat, broadcast sown
- 0.4 oz cereal rye, broadcast sown
- 0.6 oz vetch, broadcast sown
- 1.0 oz Banner fava beans, sown on 21″ centers
Steps for sowing this mix as a compost or cover crop:
- Schedule the planting date at about 6 weeks before the first hard frost date (Redding, CA = 9/30)
- Single-dig the bed by loosening the soil with a spading fork. Double-digging would be great if the bed is brand-new, but only if the soil isn’t too wet.
- Broadcast the wheat, rye, and vetch seeds separately and evenly over the bed, then chop them in lightly with a rake.
- Sow the fava beans on 21″ centers, offset (or hexagonal). Be sure the seeds are covered with a think layer of soil equal to the height of the seed when it is lying flat. Starting the fava beans indoors 10-15 days before your planting date (Redding, CA = 9/15-9/20), then transplanted out at planting time will give improved yields. For a 100 sq ft bed, this will need about 50 fava beans.