Inoculating Peas with Rhizobia Bacteria
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!
Do you know how long the inoculant is potent? Do you have to buy new stuff every year?
Many thanks, love your blog and your appearances on KUOW.
March 31st, 2010 at 11:16 amThank you so much for explaining this AND showing pictures! I’ve wondered for years if I should be doing this but never really understood why and how to do it. This helps on both fronts. Is it too late to plant peas for this year?
March 31st, 2010 at 2:50 pmVery timely information. I plan on planting peas this weekend but have never used the inoculant before (my Seattle Tilth guide says some varieties can be planted in April, if pea-enation virus resistant.)
March 31st, 2010 at 6:58 pmI’m glad to hear you talking about this. I’ve been wondering if there is a marked difference in inoculated legumes. I’ll give it a try this year. I’ll also be trying out mycorrhizal fungal applications and see what sort of magic they produce.
March 31st, 2010 at 7:19 pmMalia–I don’t know the answer to your question. I will look into it. For some reason I always lose my left over inoculant, and so I’ve always ended up buying new.
Elizabeth–It is definitely not too late to plant peas!
Leslie–Good luck planting peas. This year I’m growing ‘Wando’ English pea, ‘Super Sugar Snap’, ‘Tom Thumb’ and ‘Golden Podded Pea’.
Sputnik–Mycorrihizal fungi is supposed to be amazing! I’m curious to see how it works for you.
April 1st, 2010 at 4:57 amGreat information Willi. I’ve done it both ways. I didn’t inoculate this year. I’ll see how my peas do. We’re having a splendid spring, and I hope for a better harvest than some years.~~Dee
April 2nd, 2010 at 7:12 am.-= Dee @ Red Dirt Ramblings´s last blog ..I’m a fool for April. How about you? =-.
Very informative and well written post! Thank you for doing it, we all need reminders like this once in a while. Makes me wish I’d remembered to do this before my peas were in this year!
April 2nd, 2010 at 10:28 amThanks for the explanation of the benefits of inoculating peas. Mine are already planted and sprouting, I’ll have to try this method next season.
April 2nd, 2010 at 11:58 pm.-= Kathy M´s last blog ..Drive by Daniel Pink and the Organic Vegetable Garden =-.
From everything I have read, you cannot keep inoculant over to the next year. My little package has an expiration date of 12/10 so I think that’s probably correct.
August 6th, 2010 at 5:26 amGreat article and photos. Each year I struggle with the do I or do I not inoculate. This article helps reinforce the need and shows how easy it is.
On a side note, my history of pre-soaking peas also show a much better result when only pre-soaking for 2-4 hours vs. overnight.
February 1st, 2011 at 9:41 amI read some info stating that if you have grown peas (or other legumes before that inoculation is not necessary. The soil should contain he bacteria. You could use soil from your garden to inoculate peas/beans.
March 20th, 2012 at 9:03 pmTom–Most soils contain rhizobia bacteria, but inoculating ensures that there is a ready supply right where your legumes’ roots are. I inoculate some years and don’t others. It seems to help with yields, but it is definitely not necessary!
March 21st, 2012 at 10:21 am