Mid-April in the rainy Pacific Northwest, and our garden is covered with Fava  Bean plants--strong stems reaching straight up at waist height, loaded with fragrant blossoms, more flowers poised to emerge.  My botanist girlfriend sowed the seeds last fall after we had finished harvesting tomatoes, corn, squash, and string beans.  We've done nothing since.  The plants were a foot tall by Christmas, then waited and built root structure through the cold and dark of winter.  With the sun's return they're now exploding with life.  Lots of pollinating insects are enjoying the blossoms, including many fabulous bumblebee queens.
         We don't even much like fava beans, but that doesn't matter--we plan to chop them all down anyway in a few weeks when we plant the summer garden.  Favas make a great winter "cover crop," which becomes "green manure" in the spring.
         Legumes like fava beans and clover work with soil microorganisms to take
nitrogen from the air and "fix" it into the earth, making it available to crops that follow.  Nitrogen is an essential element in all proteins.  It's abundant in the atmosphere, but neither we nor most plants can use the gas directly.  For us to get it, it must first be fixed in the soil and then incorporated into plant tissues that we eat, or that the animals we dine upon have eaten.  Nitrogen is a primary component of commercial fertilizers, but why pay for something that nature gives us free?
         Our region's abundant rain can leech nutrients into the subsoil, deeper than the roots of corn or tomatoes will reach.  Cover crops absorb the nutrients most easily leeched by winter rains, and hold them safely until spring.  They can be part of a crop rotation plan that keeps pest insects under control, and can interrupt plant disease cycles as well.  Our favas have suppressed the growth of weeds.  Their roots aerate and loosen the soil, which will make my upcoming digging job much easier.
         Before planting the garden, we'll probably chop up and compost the fava plants for later use, while working the roots with their nitrogen-packed nodules right into the soil.  We could just till the whole plants into the earth, but then we'd have to wait a few weeks for this "green manure" to decompose before planting our garden.
         According to Organic Gardening's Soil First Aid Manual, plants get less than 5% of their sustenance from the soil--the rest from water and air.  When decayed plant material is returned to the garden, the soil thus gets a huge return on its investment.  Since plants enrich the soil, this manual says that "bare ground should make you shudder."
         Increased organic material in the soil also means more beneficial microbes, who release still more nutrients.  We rarely think of it, but we are totally dependent on the bacteria that perform decomposition.  A gram of soil may have 100 million of these microscopic critters.  Without their work, we would starve.
         We also would starve without pollinating insects.  Pollen is sometimes carried by the wind, but insects are frequently required.  Pollination is essential for plant
reproduction, and for the growth of fruits, vegetables, grains, beans, and seeds.
         My girlfriend is taking a fascinating and important class in "Pollination Biology."  Many insects (as well as hummingbirds and bats) perform "pollination services," but bees are especially important.  A few weeks ago, I wrote about the amazing lifecycle of our native bumblebees.
         I enjoy watching all the flies, wasps, ants, butterflies, honeybees, and beetles
crawling in and out of our fava bean blossoms for their pollen and nectar, but my attention is riveted by a queen bumblebee foraging.  I saw three at one time the other day.  This time of year, queens are about the only bumblebees around.  They are huge.  Each one holds within herself a potential colony of hundreds--if she finds a good nest.  In summer, only the smaller bumblebee workers are out; the queens stay in their "chambers," laying eggs and nurturing their young.
         Our fava bean patch is a rich food supply early in the season for all these creatures, and I hope it encourages the bumblebee queens to nest nearby.  Another great reason for a cover crop.
         Many different cover crops are used under various soil or climatic conditions.  Rye can survive even at 40 degrees below.  Fava beans loosen our dense soil, but barley or oats can improve soil aggregation in sandy soil.  Alfalfa fixes a stupendous amount of nitrogen.  Even weeds provide numerous benefits as a kind of "default" cover crop.  (As far as I can tell, the definition of "weed" is:  "a plant that we don't like."  Many important medicinal herbs come from "weeds."  Perhaps "invasiveness" is the best criterion for what is truly a pest plant.)
         So planting cover crops is good.  If you garden and haven't done it, try it next fall.  Many plants will work; with our climate and dense soil, my girlfriend likes fava beans and crimson clover.  Maybe we'll let some of the beans mature, and save the seeds for next fall.  Maybe we'll even get to like the way they taste sometime.
 
 
 

        Please see my related articles Food for Thought and Queen Azalea.