There’s a common saying in organic gardening: Feed the soil, not the plant. In other words, make sure your soil is healthy, and the health of your plants will follow.
In order for plants to thrive, soil needs to contain the three major plant nutrients—nitrogen, phosphorus, and potassium (the N,P, and K you see on fertilizer bags)—as well as a bunch of other secondary nutrients and trace elements.
There are many cases where we need to apply fertilizer to ensure plants have the nutrients they need, but when it comes to nitrogen (N), some plants actually feed the soil on their own. When cared for properly, these nitrogen-fixing plants reduce the need to buy, haul, and spread additional nitrogen fertilizers.
How it works
Nitrogen-fixing plants—primarily legumes but also plants from a few other families—don’t deliver nitrogen directly into the soil. Rather, nodules on their roots form a symbiotic relationship with various fungi and bacteria, which convert the nitrogen in the air into organic compounds. That process is called nitrogen fixation. Because they take care of their own nitrogen needs, these plants can often thrive in nutrient-poor soils.
The best part about nitrogen-fixing plants is that they’re beautiful as well as practical. Turn the page for four favorites to try in your garden.
Who needs nitrogen?
Nitrogen is one of the three most important nutrients for plants (along with potassium and phosphorus). It helps plants grow and develop, make food for themselves through photosynthesis, and take up water through their roots. It’s also part of the plant structure—you’ll find it in leaves, grains, plant tissues, and roots.
Lupine (Lupinus perennis, Zones 3 to 8). With showy flower spikes up to 5 feet tall, lupine is a gorgeous perennial wildflower. It prefers well-drained soil and full sun. Afternoon shade is helpful in areas with hot summers. Lupine thrives with deep, infrequent watering and does well in dry, rocky soil. Drip irrigation helps decrease the chance of mildew in hot, humid climates.
Sea buckthorn (Hippophae rhamnoides, Zones 3 to 9). Terrific for hedges and erosion control, sea buckthorn is one of the most widely grown cold-hardy, fruiting plants in the world. Its edible berries—which taste like orange and passion fruit—are packed with vitamin C and make delicious juice and jams. (It’s a dioecious species, so you’ll need a male and female plant in order to get fruit.) This 6- to 10-foot-tall narrow shrub prefers full sun and good drainage. And don’t worry—it’s not related to common buckthorn (Rhamnus cathartica) or glossy buckthorn (Frangula alnus), the invasive shrubs that degrade natural habitats in parts of the United States and Canada.
Siberian pea shrub (Caragana arborescens, Zones 2 to 8). Loved by bees and butterflies for its bright yellow spring flowers, this fast-growing shrub grows 10 to 15 feet tall. Siberian pea shrub prefers full sun and good drainage. Once it’s established, it is drought tolerant and can handle extreme cold. Good as a hedge and for erosion control, it has seedpods that attract wildlife.
White clover (Trifolium repens, Zone 3 to 9). White clover, also called Dutch clover or shamrock, is a 2- to 8-inch-tall flowering perennial. Some consider it a weed, and it can be aggressive, but it’s great as a cover crop to prepare a garden bed or to replenish a large area of soil. Sow seeds in summer or fall for vigorous, nitrogen-rich spring growth. The plant spreads by creeping, rooting stems, and it is self-sowing. Mow down, till, or pull it by hand when it’s flowering but before it sets seed. You can also plant it in lawns, as a ground cover, and for erosion control. When mixed in with grasses, it can provide up to one-third of the nitrogen your lawn needs. It can handle poor soils but doesn’t do well in dry conditions.
More nitrogen-fixing plants
Want more plants that can thrive in poor soil? Try these nitrogen-fixing trees and shrubs:
Alder (Alnus spp., Zones 2 to 8, depending on species)
Black locust (Robinia pseudoacacia, Zones 4 to 9)
Silver buffaloberry (Sheperdia argentea, Zones 2 to 6)
Sweet acacia (Acacia smallii, Zones 7 to 9)
Wax myrtle (Myrica cerifera, Zones 6 to 10)
Wild indigo, shown in the photo above (Baptisia australis, Zones 3 to 10)
Wild lilac (Ceanothus spp., Zones 1 to 9, depending on species)