Since I was a little kid, I’ve looked up to George Washington Carver. The man came up from slavery and fought his way to the top despite opposition, was unabashed in his Christian faith, led a college agricultural program, was an artist, experimented endlessly… and made roughly 1.9 zillion things from peanuts and sweet potatoes.
In particular, George Washington Carver’s work with peanuts has filtered down into mainstream culture, though most people don’t really know why he did what he did.
His experiments with crop rotation allowed the depleted soils left behind by years of cotton farming to regain productivity. The reason peanuts played heavily into this plan? Nitrogen!
Like many members of the bean and pea family, peanuts have a special relationship with certain soil bacteria that allow them to “fix nitrogen.” Basically, these microbes live on the roots of certain plants, enjoying the sugars exuded, and paying for their rent by taking nitrogen from the air in the soil and converting it from an unusable atmospheric form into a form that can be used by plants.
In its simplest form, when you plant plants that ad nitrogen to the soil, you’re fertilizing from THIN AIR. That alone is a great reason to add these powerhouses to your garden plans… even if you don’t use them to make candy, ink, shampoo, margarine, rubber, ropes, cloth, deodorant…
Adding Nitrogen Fixers To Your Garden
Are you growing beans or peas? Then you’re adding nitrogen to your soil. I’ve read that the highest yield of nitrogen can be reached by tilling under nitrogen fixing plants right before they fruit; however, that means you won’t get frustratingly tiny amounts of beans. Heh heh.
To utilize the power of nitrogen fixers in a really cheap way over a large area, you can buy cheap bags of beans, raw peanuts, peas and lentils from the supermarket and scatter them across unused beds and newly tilled ground. In the summer, I stick to warm-weather nitrogen fixers like southern peas, limas, kidney beans, peanuts, etc. In the fall, winter and spring, I plant lentils, chick peas, fava beans and dry peas. It doesn’t matter if these plants ever produce anything: they keep the ground covered and alive while adding valuable nitrogen. To get the best bang for your buck, you can snip them off at ground level or till them under before you plant your next crop and let the nitrogen-nodule bearing roots rot beneath the ground. Yanking them out removes too much.
Though it’s disputed, I believe that nitrogen fixers feed the plants around them even without being tilled under. That’s why I often mix lentils and peas in with my cabbages and scatter beans around my fruit trees.
Using Nitrogen Fixers in Your Orchard or Food Forest
When permaculture gurus plan a “food forest,” they make liberal use of nitrogen fixing trees and shrubs. By adding these fertilizer producers, they can feed the young food-producing trees near them without adding extra chemical or organic fertilizers. Basically, they’re growing fertilizer in place. In my food forest, I’m growing some plants of questionable nitrogen-fixing ability (honey locust, Senna alata) along with proven nitrogen fixers like Leucana, pigeon pea, coral bean, mimosa trees and multiple varieties of Eleagnus. (Eleagnus species are special: they aren’t in the pea and bean family, plus they grow edible fruit. Doubleplusgood!) If I remember, I also throw around southern peas and other annual nitrogen fixers when I break up an area of ground or plant new trees. There are a lot of options on this front, especially if you’re not trying to grow anything edible. Lupins, vetch, velvet beans, clover… there are plenty to choose from. Many nitrogen fixing plants are also fast growers, which means they can be cut regularly and thrown around more important plants (like your apple tree) as mulch, or simply composted and fed to the soil in needy places.
One problem you may have when you look for nitrogen-fixing trees: many of the very best have been added to lists as “invasive” species. I don’t fear invasive species, since I’m an active gardener, but I know a lot of people that find them terrifying… including the USDA. If it’s a variety that makes tons of seeds and dumps them all over, cut off the blooms when they form. If it’s a species that climbs far up into your neighbor’s trees, keep it from doing that. Kudzu was originally planted as a great nitrogen fixer… and look how helpful it’s been. Nitrogen fixers are the elite forces of the Plant Kingdom. They were designer to take care of themselves, repair the soil and pave the way for less-hardy species. Remember this… or they may eat your garden.
Just be smart and let the plants work for you. If you incorporate nitrogen fixers into your planning, it means you’ll have a lot less need for fertilizer. Plus, you’ll also get some great food from some species. Like George Washington Carver, nitrogen fixers leave the world behind them a better place.
Now I want peanut butter…