How do plants get nitrogen? It’s one of the most important nutrients your plants need whether you’re grow bag gardening, growing from raised beds or in a traditional garden. Plants need nitrogen for their photosynthesis process, to make amino acids, and for the nuts-and-bolts of being alive and growing. While gardeners often add nitrogen-rich fertilizers to boost growth, plants also access this essential element through natural processes and even with a little help from microbes and lightning. Understanding how nitrogen reaches your plants can help you make smarter, more sustainable choices for your garden.
Why Plants Can’t Use Atmospheric Nitrogen
Here’s something interesting. 78% of our atmosphere is nitrogen. Why don’t the plants just put that to use? They already take carbon from the air to build their structures, and carbon dioxide represents just a tiny 0.04% of Earth’s atmosphere. So, when plants need nitrogen, and there is a whopping 78% of the atmosphere in nitrogen right there up for grabs, why don’t they use it? Why do gardeners and farmers sometimes need to supplement nitrogen?
The answer lies in a bit of simple chemistry. Nitrogen, if you recall from the periodic table, is an element, consisting of a single nitrogen atom, signified by the letter N. But the nitrogen in our atmosphere isn’t formed from single, independent nitrogen atoms. It’s a pair of nitrogen atoms joined together—written N2. Nitrogen atoms are highly reactive and snap together in a way reminiscent of two magnets. It takes a good deal of energy to break them apart again. But plants can’t put N2 to use—it’s just not a form they can utilize or have the ability to break apart.
How Synthetic Nitrogen Fertilizers Are Made
To help solve this problem, farmers and gardeners often use human-manufactured forms of nitrogen. In this case, we take N2 from the air—which is abundant—and use hydrogen (usually from natural gas) and pressure to facilitate a series of chemical reactions designed to break apart the bond of N2. The result is typically some sort of ammonia or similar compound, which can be easily applied to crops. In fact, 2% of all the world’s energy goes towards the industrial process of converting N2 into other plant-friendly forms.
Natural Ways Plants Get Nitrogen
But obviously, plants were growing just fine for millennia before the Green Revolution. Where did their nitrogen come from before that? In nature, a surprising alliance of lightning, bacteria, and other microbes performs this work. First, high-energy lightning activity in the atmosphere combines nitrogen with oxygen to form nitrates, which enter the ground with rain. Some microbes in the soil, in a symbiotic relationship with a plant’s roots, convert the nitrates into plant-friendly ammonia compounds, ready for the plant to absorb and utilize.
Nitrogen-Fixing Plants That Enrich Soil
Legumes—beans, peas, peanuts, alfalfa, clover, and others—actually restore nitrogen to the soil thanks to that same symbiotic relationship with soil microbes. Amending soil this way is called nitrogen fixing. Rotating crops is a nice natural way to increase soil nitrogen—you can plant a legume for a year, then something else, then return to the legume.
Final Thoughts: Feeding Plants the Right Way
Understanding how plants get nitrogen helps gardeners make informed decisions about soil health and plant nutrition. Whether you rely on organic methods like planting legumes or supplement with store-bought fertilizers, knowing where nitrogen comes from and how plants use it can lead to healthier, more productive gardens. With a bit of science and strategy, you can keep your soil healthy and your plants thriving.
This story about how plants get nitrogen was written for Hobby Farms magazine. Click here to subscribe.
