11 Nitrogen-Fixing Plants That Will Improve Your Garden Soil

Earth’s atmosphere is made mostly of nitrogen (N), but this crucial nutrient isn’t automatically available in a form that plants can digest. Enter our beloved nitrogen fixers, many of which are in the Fabaceae family and are known as legumes. These plants have a symbiotic relationship with Rhizobia bacteria on their roots.

The bacteria convert atmospheric N into a digestible form for plants, which is how these plants uptake most of their nitrogen. Then, as these plants decay, they leave available N behind to nourish other plants.

Clover

	common name Clover
	botanical name Trifolium spp.
	sun requirements Full sun to partial shade
	height 6”-24”
	hardiness zones 3-10

Many gardeners don’t realize that the clover weeds that pop in their lawns are actually members of the family Fabaceae and are excellent nitrogen-fixers. There are multiple clover species you can use for crop rotation, including the common white clover (T. repens) and red clover (T. pratense), as well as crimson clover (T. incarnatum).

White and red clover are herbaceous perennials typically considered weeds, but that doesn’t mean they don’t have their purpose in the garden when it comes to fixing nitrogen. One healthy acre of clover can fix up to 200 pounds of N, so you should not overlook clover. However, grow one that is not invasive to your region if at all possible. 

Crimson clover is an annual that offers more ornamental value with bright, red flowers. It’s often grown as a summer annual in zones 3-4 and a winter annual in zones 6-9. This means crimson clover will die at the end of its season, though it may spread seeds that re-emerge next season, depending on your climate.

Most clover species prefer well-drained soils and lots of sunlight, though partial shade will satisfy white clover. They have moderate watering needs and can be somewhat drought-tolerant. Growers are likely already familiar with the needs of white and red clover, which spread via stolons throughout their grass.

Peas

	common name Peas
	botanical name Pisum sativum
	sun requirements Full sun to partial shade
	height 2’-6’
	hardiness zones 2-11

If you’re looking for a cover crop that also provides edible harvests, don’t sleep on the humble pea. This nitrogen-fixing plant is perfect for vegetable garden rotations. Cool-season edible varieties are ideal as a spring or fall crop, and can grow in winter in some areas. With a hardiness range of 2-11, really any gardener can stick some peas into their schedule, adding N to the soil.

Pea plants get 80 percent of their nitrogen from fixation, enriching the soil for upcoming crops. Support your peas with moist, well-drained soil and plenty of sunlight. They’ll get by in partial shade, but if you want them to flower and fruit, opt for full sun.

You can plant both bush varieties or vine varieties of peas. If you’re hoping for nitrogen fixation over a large area, a thorough scattering of bush peas may be the right choice. But if you just want to enrich the area around a trellis, try growing some vining peas.

Alfalfa

	common name Alfalfa
	botanical name Medicago sativa
	sun requirements Full sun
	height 2’-3’
	hardiness zones 4-11

There are many reasons to grow alfalfa, another perennial from the legume family. Alfalfa sprouts add a healthy, delicious crunch to sandwiches, livestock benefit from alfalfa’s nutritious makeup, and lastly, alfalfa is another cover crop that fixes a significant amount of nitrogen.

Alfalfa is truly a nitrogen-fixing powerhouse. One acre of this Fabaceae family member can fix up to 300 pounds of nitrogen. If you’re gardening at a large scale, that’s an immense amount of N that could otherwise be a strain on the wallet.

Plant alfalfa in well-draining, neutral soil in full sunlight. Alfalfa will struggle in acidic soil. These plants may get up to three feet tall, and their purple flowers attract pollinators. Also, alfalfa is edible beyond its sprout stage. You can eat any part of the plant, though its leaves are most mild when young.

This nitrogen-fixing plant grows best in cooler temperatures, so depending on your zone, alfalfa may be more of a spring or fall crop. Water alfalfa consistently during hot, dry periods, but avoid overwatering. Alfalfa plants do not like to sit in water and are somewhat drought-tolerant, so take note of recent precipitation.

Fava Beans

	common name Fava Beans
	botanical name Vicia faba
	sun requirements Full sun
	height 2’-7’
	hardiness zones 2-10

Fava beans are known for their nutritious content, both high in protein and fiber. These nitrogen-fixing plants are often grown for their edible pods, but they’re also a staple cover crop. A member of Fabaceae, fava beans and their bacterial allies are incredibly efficient at nitrogen fixation. They typically don’t need any fertilizer.

High up on the list of best nitrogen fixers, a cover crop acre of fava beans can provide around 250 pounds of N. Other similar grain legumes that perform as well include black-eyed-peas and soybeans.

Fava bean plants prefer cool climates, so plant them in spring. They can germinate at temperatures as low as 35°F (2°C). You may discover that fava bean plants don’t grow as well if planted during hotter times of the year.

These plants require about five months of growth before you’ll be able to harvest any fava beans, but all the while they’ll be enriching your soil.

When choosing fava beans, make sure you plant the right kind. The broad bean variety (V. faba var. major) produces the large, edible beans you might enjoy with dinner, while the field beans variety (V. faba var. minor) is meant for feeding livestock. Both are great nitrogen fixers.

Partridge Pea

	common name Partridge Pea
	botanical name Chamaecrista fasciculata
	sun requirements Full sun
	height 1’-3’
	hardiness zones 3-9

If you’re looking for a low-maintenance plant that both fixes nitrogen and catches the eye with attractive flowers, look no further than the partridge pea. Bright yellow flowers emerge in summer and remain until frost with enough rain, bringing pollinators to your garden.

Partridge pea has gentle leaves that fold when touched and fold at night, similar to the sensitive plant (Mimosa pudica, which is also technically a legume). This species may not provide edible fruits like peas or fava beans, but it offers ornamental value and support for wildlife.

An herbaceous annual, partridge pea is native to the eastern U.S. and is planted for multiple purposes beyond its excellent nitrogen fixation. It’s considered a pioneer species, happily populating depleted sites and disturbed areas, providing a path for more plants.

Partridge pea is easy-going. It prefers well-drained soil and full sunlight. You’ll want to give it some water, though these plants are drought-resistant. You can even plant them on slopes, where they help prevent erosion.

Gardeners in zones 3-9 can all grow partridge peas. In ideal climates, this plant becomes somewhat weedy. Even though it’s an annual, it self-seeds readily. However, partridge pea offers so many benefits to the garden and local wildlife, including songbirds, butterflies, and quail, that weedy growth is no cause for alarm.

Hairy Vetch

	common name Hairy Vetch
	botanical name Vicia villosa
	sun requirements Full sun to partial shade
	height 1’-3’
	hardiness zones 3-10

Hairy vetch is planted in the fall and grown through winter. There are multiple species in the vetch genus that help enrich soil. Hairy vetch may be the most effective, but the others are fine choices as well. Choose one that won’t invade and crowd out native plants and wildlife. 

This species really takes off in spring after a long winter of establishing its roots. Thick cover crops of hairy vetch add nitrogen and also prevent weeds from emerging in your garden beds. This species even helps resist erosion, and once it dies, hairy vetch forms “dead mulch,” adding even more nutrients to the soil. 

The list of hairy vetch cover crop benefits continues, as this legume promotes healthy soil structure throughout winter, feeding microorganisms well below the surface. It also increases water retention. It doesn’t hurt that hairy vetch has pretty purple flowers in spring, too. 

Hairy vetch loves to climb when it can, so consider growing it in combination with rye. While rye also helps reduce erosion and suppress weeds, it can also act as a trellis for hairy vetch to climb. Working in tandem with both species can have a significant, positive effect on your soil.

Lentils

	common name Lentils
	botanical name Lens culinaris
	sun requirements Full sun
	height 1’-3’
	hardiness zones 7-12

Farmers have cultivated lentils for thousands of years, and they are a dietary staple around the world. Like all the other species on this list, lentils are legumes, so they’re packed with protein and fiber. Plus, lentil plants are great at fixing nitrogen.

These plants get about 80 percent of their N through fixation, just like peas. To grow lentils, plant them in spring, and they’ll be ready to harvest in fall. A full season of lentils in a garden plot will result in plenty of available N in the soil.

Lentils aren’t picky about soil type as long as it drains well. They need full sunlight to grow to their maximum potential, and their watering needs are moderate. Make sure they get about an inch of water per week, possibly more during the hottest parts of the season.

However, in order for lentils to do their best nitrogen-fixing work, gardeners should manually inoculate the seeds with rhizobia before planting. The process is simple. You basically just wet the seeds and sprinkle the inoculate on them. Studies have shown that this increases harvests and improves nitrogen fixation.

Chickpeas

	common name Chickpeas
	botanical name Cicer arietinum
	sun requirements Full sun
	height 1’-4’
	hardiness zones 3-9

Chickpeas, also known as garbanzo beans among many other names, are eaten all over the world. Vegetarians in particular tend to appreciate chickpeas for their high protein content. Aquafaba from chickpea liquid is even used as an egg substitute in vegan cuisine.

Carnivore, omnivore, or herbivore, one thing is for sure: Chickpeas add tons of N to your soil. Yet another member of the legume family, chickpeas are nitrogen fixers that assist in making the vital nutrient available.

Chickpeas have a fairly long growing season, so plant them as soon as the last frost has passed. They prefer full sunlight and will not be as prosperous in partial shade, though they’ll still perform nitrogen fixation. Chickpeas also prefer well-draining soil.

These plants offer additional soil benefits as cover crops, too. They can break up compacted soil with their impressive roots. These roots make the plants drought-tolerant as well. Chickpea plants will also suppress weeds when planted densely.

Lupine

	common name Lupine
	botanical name Lupinus spp.
	sun requirements Full sun to partial shade
	height 1’-3’
	hardiness zones 4-8

Lupines are another ornamental option for nitrogen fixation, and there are multiple species and varieties of lupine that you can grow. The classic wild lupine (Lupinus perennis) has bluish-purple flowers and is a native perennial in mild temperate zones.

Because these plants fix nitrogen for themselves, they don’t need nutrient-rich soil. Plant them wherever nutrients have been depleted. They’ll do fine in these poor soils, fixing nitrogen themselves and leaving the soil in better shape with time.

Lupine may not look much like its legume family members, but it can fix just as much N, supplying comparable amounts per acre to clover and hairy vetch.

When planting lupine, choose a fairly sunny spot. Full sun is not needed, but these plants do need at least a few good hours of sunlight per day. Their bright flowers will attract bees and hummingbirds. Wild lupine is even a host plant for the endangered Karner blue butterfly. 

Beyond classic L. perennis, check out ‘Russell Blend’ or ‘Pixie Delight’ for more colorful lupine options that include red, yellow, and pink flowers. All will have a similar effect within your garden soil.

Peanuts

	common name Peanuts
	botanical name Arachis hypogaea
	sun requirements Full sun
	height 9”-18”
	hardiness zones 2-11

Peanuts are yet another outstanding choice for fixation, as they’re on par with fava beans when it comes to leaving available nitrogen in their wake. There are multiple varieties of peanuts to choose from, including the common Runner peanut, Virginia peanuts, and Valencia peanuts.

Plant peanuts as a cover crop in between other species, and peanuts will provide ground cover for your soil. This will help suppress weeds and will eventually result in more organic matter once the peanut plants have finished their lifecycle, beyond just nitrogen.

Peanuts grow a bit differently than most edible legumes. First, the flowers self-pollinate, and then they form what is called a “peg.” These pegs penetrate the soil and go about one or two inches deep. These below-ground pegs then develop into peanuts.

These plants prefer full sunlight, so make sure they get at least six hours of direct sun if not more, and they grow best in well-drained soils. Peanut pods can take up to 150 days to fully ripen, if you’re growing the plants to eat and not just as a cover crop. 

To harvest, dig up peanut plants after the first frost and spread them on a dry surface. They will need additional time to cure before you can separate the peanuts and enjoy them.

Sweet Pea

	common name Sweet Pea
	botanical name Lathyrus latifolius
	sun requirements Full sun
	height 6’-9’
	hardiness zones 4-8

Last on the list is perennial sweet pea, also known as everlasting pea, which is a climbing vine known for its beautiful pink flowers and amazing fragrance. There are multiple cultivars of L. latifolius, and you can also plant one of many cultivars of L. odoratus, which is also referred to as sweet pea.

Both species and all their cultivars are in the Fabaceae family, fixing nitrogen. Between these many sweet pea options, there is a long list of flower colors available, including pink, red, blue, and white. Like lupine, sweet pea is a stunning ornamental option.

Sweet pea climbs, just like many of its legume family members. If you are growing cucumbers, tomatoes, or another vining edible up a trellis or fence, rotating it with sweet pea is an easy way to enrich the soil between crops.

Grow sweet pea in full sunlight and in well-drained soil. Perennial sweet pea doesn’t love being transplanted, so direct sow these cold-hardy seeds. You can plant them a month or two before your last frost date.

If you want a fragrant flower, consider ‘High Scent’ sweet pea, or the deep red ‘Beaujolais’ cultivar may interest you. For a colorful blend of big, bold blooms, explore ‘Mammoth Blend.’