What Are Nitrogen-Fixing Plants and Why You Should Be Growing Them

Most plants grow such that their roots wiggle and wind into the soil picking up nutrients from what’s around. Plants, in particular, love to find little deposits of nitrogen in the ground, which is their version of a stomach filler, the main dietary fuel of the plant world. Plants need nitrogen to create protein so that they grow and chlorophyll to photosynthesize, so it’s essential for growing a good garden or even a lawn.

That’s why when we buy fertilizers, there is usually the NPK listing, N being nitrogen (P for phosphorus and K for potassium). When we add compost to the soil, we do so, at least in part, because it is rich in nitrogen. The same goes for animal manure (for those who do that). The chewed-up grass clippings the mower spits back onto the lawn are high in nitrogen.

But, there are a group of select plants that have a special talent: they take nitrogen from the air (roughly 78% of it is nitrogen gas) and convert it into nitrogen in the ground, where roots can suck it in as a nutrient. These plants, then, can create their own source of nitrogen fertilizer. Thus, they are called nitrogen-fixing plants.

What Are Nitrogen-Fixing Plants?

In reality, nitrogen-fixing plants are “fixing” nitrogen into the soil all on their own. What happens is that the roots of nitrogen-fixing plants have little nodules—environments—that are perfectly suited for the types of bacteria that take atmospheric nitrogen (N gas from the air that plants can consume) and converted into ammonium, nitrate, and nitrate (all of which plants roots can then feed on).

In other words, the actual conversion of nitrogen from the air to nitrogen in the soil isn’t done by the plants but by the soil life—specific types of bacteria—living on the roots of the nitrogen-fixing plant. The root-dwelling bacteria feeds on the atmospheric nitrogen and poops it out as ammonia (NH4+). Then, different bacteria feed on that and create nitrite, feeding other bacteria that create nitrate, the favorite version for plants.

Why You Should Be Growing Nitrogen-Fixing Plants

When we put fertilizer in the garden, we are simply skipping this biological sequence and getting straight to the nitrate. While this may seem simpler, it is largely lacking as a nitrogen solution. Because the nitrogen in fertilizer is loose (not bound up in bacteria), it becomes a serious environmental problem.

• It is prone to running off into water sources, making them overabundant in nitrogen and dangerous.
• It is more volatile and turns into nitrous oxide, a problematic greenhouse gas.
• The concentrated quantities of nitrogen irritate the soil organisms, our natural nitrogen producers, making us reliant on chemical nitrogen instead of biological processes.
• Furthermore, these soil organisms did more than supply nitrogen, they helped plants get all the other macro-and micro-nutrients they needed.
• When plants don’t get these other nutrients, the crops that we get from them are lacking those nutrients, too, so we get less nutritious food.

Nitrogen-fixing plants are a way that we can naturally encourage the right types of soil organisms to hang around and call their friends over. The soil around them becomes rich in those organisms and, thus, rich in nitrogen for the plants. This nitrogen, unlike fertilizers, is wrapped up in biological processes, however, so it doesn’t cause all the negative results.

Which Plants Are Nitrogen-Fixers?

There are thousands of species of nitrogen-fixing plants, some of which are small and herbaceous and others of which are gigantic trees. In other words, whether you are trying to add nitrogen to a tiny raised bed garden or a massive food forest, there are nitrogen-fixing plants to fit your needs and space.

There are nitrogen-fixing plants that a great for the garden, both as a cover crop when not growing vegetables or traditionally as companion plants to the other vegetables. Cover crops include different types of clover, vetches, lupins, alfalfa, and field peas. As for growing nitrogen-fixers as companion plants, green beans, garden peas, peanuts, and soybeans all work.

For grander endeavors like mixed-fruit orchards, the nitrogen-fixing plants can be larger. Trees can range from desert-dwellers like mesquite and acacia to temperate climate species such as Siberian pea trees and alders. There are also berry-producing shrubs like sea buckthorn and goumi berries.

In other words, there is a nitrogen-fixing plant, usually a number of them, to fit just about every need, from small spaces to pasturelands, from arid climates to rainforests. And, cultivating these types of plants in our garden systems is a key ingredient to producing food sustainably and improving the environment rather than destroying it.

Related Content:

• 7 Plants That Enrich Your Garden Soil
• 8 Perennial Plants for the Veggie Patch: They Just Keep Coming Back!
• 7 Permaculture-Recommended Plants You Should Include in the Garden

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