In mild climates, the seeds can be sown as early as late January. Fava beans grow best in daytime temperatures of 60°F to 65°F, so time your plantings accordingly in either season.
Cut down the plants at soil level while they’re in peak bloom. Dig them under a bit and spread a layer of mulch over the bed to maximize nitrogen retention.
(Note that leaving the decomposing plants near the surface provides slow-release nitrogen to new plants, while breaking them up and burying them several inches deep adds a quicker dose of nitrogen.)
Do the chop-and-drop about two to three weeks before you want to plant in the same spot. When your new seedlings are ready, you can just push the mulch aside to transplant.
Live in a mild climate? Fava beans can be sown year-round in areas with Mediterranean-like weather (such as the California coast) where winters are warmer and summers typically don’t go above 75°F. (Between May and August, it’s best if your fava crop has some morning fog or afternoon shade.)