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How To Use Simple Seed Inoculant To Start Healthy Seedings

The world “inoculant” might call to mind visions of vaccination, but the science of plant immunity works differently than human biology. Vaccinations work by introducing a foreign substance into a host to preemptively fight infection, while seed inoculants serve a slightly different purpose. 

Seed inoculations improve plant health by ensuring a strong foundation from the beginning. Some plants depend on symbiotic relationships between their roots and soil-borne bacteria or fungi to receive the nutrients that they need to thrive.

The intent behind inoculating seed is simply to jumpstart an already natural process by making the partners that much more readily available to one another. Read on to understand how and when to use seed inoculant and where to buy it! 

What is seed inoculant?

There are a few different inoculants on the market, including mycorrhizae seed treatments that introduce beneficial fungi to plant root systems. But for most home gardeners, the most important seed inoculants are those that contain Rhizobium bacteria. 

A naturally occurring bacteria in the soil–Rhizobium–has a critical partnership with plants in the legume family that farmers and gardeners have utilized for centuries. This natural process of nitrogen-fixing led to the development of seed inoculants, explaining its importance today. 

The process of nitrogen-fixing

As you’re well aware, legumes like peas and beans are nitrogen-fixers–these super plants mysteriously convert atmospheric nitrogen into a form that they can metabolize. It’s also why legumes like clover and vetch are perfect cover crops–they enrich the soil with nitrogen for years to come. 

The key player in the nitrogen-fixing process is Rhizobium bacteria. Rhizobium has a symbiotic relationship with legumes–it’s not the pea plants that fix nitrogen in the soil; it’s the bacteria. The plants provide the bacteria with a food source (sugar), and the bacteria Rhizobium processes nitrogen into a form that plants can use. 

pea plant in garden

Why use manufactured seed inoculant?

If Rhizobium already exists naturally in the soil, you might wonder why you would need to purchase nitrogen inoculant. This is one scenario where more actually is better. All too often, our native soils are overworked and undernourished, so it doesn’t hurt to add inoculants when planting legumes like beans and peas.

Inoculants boost plant immunity, resulting in larger plants and higher yields. Fortunately, nitrogen inoculants are inexpensive and readily available. Whether you’re growing Crimson Clover as a cover crop or Sugar Snap Pea for snacking, pairing your legume seed with Nitrogen Inoculant will mean more bang for your buck. 

How to apply seed inoculant

Nitrogen inoculant is usually sold in a powdered form, sometimes mixed with peat moss, and is very easy to apply. There are a couple of different ways to adhere the bacteria to the seed, and either method works great! 

Coat seed in inoculant

The most popular technique to coat legume seeds with Rhizobium bacteria is to spread the powder in a layer and roll the seed around until it is thoroughly coated in the inoculant. Be sure to wear gloves anytime you handle inoculant, and avoid breathing the powder. 

Some gardeners use a sticking agent like honey or molasses to help the inoculant adhere to the seed. Simply mix your adhesive with warm water, dip the seeds in the mixture, and then roll them in the powder as described above.

You can soak your pea seeds prior to coating them if you plan to plant them the next day. Soaking seeds will kickstart the germination process, so soaked seeds can no longer be stored long-term. Limit the soak time to 12 hours or less, and once you’ve drained your seeds, you can roll them in the inoculant. Then they’ll be ready to sow! 

Add inoculant as seeds are sown

An alternative method is to sprinkle the inoculant as you sow seeds. This method is better suited for direct-sown seeds–dig a furrow in which to plant your pea and bean seeds and line the furrow with a dusting of Rhizobium bacteria. Be generous–you really can’t overdo it with nitrogen inoculant! 

Be sure to amend your garden beds with compost to add organic matter that the bacteria (and your legumes) will appreciate. Hold off on fertilizing, however. It’s recommended to inoculate and fertilize seeds at different times since the young bacteria can be burned by fertilizer. 

Store inoculated seeds

If you want to prepare your seeds long before sowing them, you can store inoculated seeds–carefully. Pre-inoculated seeds will store for up to a year in a cool, dark place. If you leave your seeds past the inoculant’s expiration date, simply coat the seeds with fresh inoculant, and they’ll be ready to sow. 


Inoculating legume seeds like peas, beans, and clover isn’t essential–but it is the best way to maximize crop harvests and fix nitrogen in the soil. You’ve already invested in quality seeds–why not ensure those seeds produce to their potential by adding an inexpensive nitrogen inoculant? Your soil (and your garden) will thank you for your extra effort with the biggest harvest you’ve seen yet.

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