A couple years ago I started to occasionally inoculate my peas with rhizobia bacteria before planting. I noticed that when I inoculated, my plants were definitely healthier and had heavier yields then when I did not inoculate. A lot of gardeners never inoculate their peas, which is fine, but I thought I’d explain what it is, how you can apply it to your seeds, and why you might want to bother with it in the first place.
Peas belong to the legume family, which also includes beans, favas, and lentils (as well as clover, wisteria and a host of other plants). Legumes have a special relationship with rhizobia bacteria. These tiny microorganisms act like little nitrogen factories. They form nodes on the roots of legumes and convert nitrogen in the air (which plants don’t have access to) and fix it into the soil in a form that the legumes can use. In return, the legumes provide the bacteria with essential carbohydrates and minerals. Rhizobia bacteria live in most soils, but inoculating the peas with rhizobia bacteria improves node formation on their roots and nitrogen fixation rates.
To inoculate peas, start by soaking them in water. This helps soften up the seed coat, which makes the seeds germinate faster once they are in the soil. I’ve had better germination rates soaking the seeds for about two to four hours, rather than overnight. My (unscientific) theory on this is that leaving the peas to soak overnight allows them to imbibe too much water.
Different strains of rhizobia bacteria exist, so be sure to purchase a packet of inoculant that is formulated for garden peas (Pisum sativum). Most well-stocked nurseries carry incoulant and it can also be ordered online from seed catalogs and Peaceful Valley Farm Supply.
Pour a few tablespoons of the inoculant into a resealable plastic bag. Drain the water off the peas and place the damp pea seeds into the bag with the inoculant.
Zip the bag shut and give the peas a good shake to cover them with the darkly colored inoculant. Then, plant the inoculated peas out into the garden. I like to space mine close together, about 1 inch apart, and then thin the plants to two inches apart when they are six inches tall. Just be sure not to toss those thinnings—they make the most fabulous salad greens!