Secret life of St. Paddy’s peas

The tradition of planting peas on St. Patrick’s Day, March 17, came to America with the Irish and is still the official reminder date to put pea seeds in the ground that can be worked. Of course you must adjust your date to allow for snow to melt and soil to thaw, but while conditions are still cool in the dawn of spring, peas thrive.

Peas share a secret life with other members of the legume clan. It all happens underground in their roots for one of the most amazing relationships in home gardening. It’s important because this secret can double your yields.

A pea seedling root encounters a particular fungus present in the soil. Fungus enters the root to create a symbiotic relationship that benefits both pea and its hitchhiker. This team effort allows the plant to take in atmospheric nitrogen through the foliage and transfer it to the roots. Nitrogen can actually be added to your soil by pea plants, and there’s a bonus at the end of their cycle when dead pea plants are composted or tilled in.

This miracle is achieved by a fungus called Rhizobium leguminosarum biovar vicaea. It takes weeks for naturally present rhizobium in your own soil to begin this important process. With pea crops maturing in just 60 days, there’s not much time for this natural process to reach its peak effectiveness. Speed it up by introducing rhizobium to your pea seed before you plant it.

Peas well established with plentiful rhizobium will be much stronger, larger and yield better. This is doubly important in soils that lack microbial populations and are nitrogen deficient. More symbiotic rhizobium in the plant means it can draw more nitrogen from the air and use it to grow. Once you’ve introduced the rhizobium to your garden via pea seed, it becomes more plentiful in the soil naturally. Next year your peas, beans and other legumes will grow better without inoculation.

Most seed catalogs offer rhizobium products formulated for peas and beans, the two most popular home grown legume crops. It’s typically a powder that’s applied to your seed before planting. Instructions for the product will give you the step by step process of inoculating your seed with rhizobium.

When ordering (I order from Johnny’s Selected Seeds at because they have a great selection of edible pod pea varieties), look for rhizobium to order with your pea seed. The one you want is called “lentil and vetch inoculant,” which is safe and non-toxic to increase vigor and yields. Save enough product to treat your summer bean seeds as well. Always buy fresh rhizobium packaged for the present year because it’s a living thing that loses viability rapidly.

If you’re looking for an early crop that matures before you plant your summer veggies, sow on St. Patrick’s Day before you celebrate. The next morning that rhizobium goes to work getting your peas off to a great start, while you nurse that hangover in bed.

Maureen Gilmer is an author, horticulturist and landscape designer. Learn more at Contact her at or P.O. Box 891, Morongo Valley, CA 92256.


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