How To Add Nitrogen To Soil Organically (10+ Ways!) - Growfully

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While there are three macronutrients gardeners need to stay on top of—NPK, nitrogen, potassium, and phosphorus—it seems like nitrogen is the nutrient folks are most concerned about—and for good reason!

Without a strong source of nitrogen, your vegetable plants can suffer from slowed growth, low yields, and lack of color. Eventually, poor nitrogen reserves can make your plants weak enough that they more easily succumb to diseases and pest infestations. So let’s figure out how to get nitrogen to your plants so you can have a bumper crop of your favorite veggies!

Why do plants need nitrogen?

Think of nitrogen as the main fuel for plant growth. Nitrogen’s main purpose is to help plants grow big, lush, green foliage and stems. Nitrogen is used in many processes in the plant—to synthesize amino acids, proteins, chlorophyll, and enzymes.

A good nitrogen source helps your plant grow big and strong, which allows them to more easily set fruit (if you’re growing a fruiting variety), roots (for root crops), or lush leaves (for greens and other leaf veggies).

Signs of a nitrogen deficiency

The #1 sign that your soil doesn’t have enough nitrogen is stunted plant growth—but often that can be hard to pick up on if you are a new gardener or don’t have another healthier plant to compare it to.

The easiest to spot sign of a nitrogen deficiency is yellowing or lightening of the leaf color of your plant—called chlorosis. Nitrogen-deficient plants tend to have leaves that take on a yellow-green tinge—or even go full yellow if the nitrogen is low.

Soil testing for nitrogen deficiencies

Unfortunately, soil testing for nitrogen is tricky, because nitrogen availability is impacted by many different factors (weather, moisture, type of plant). By the time you have taken your soil sample, sent it to the lab, and it’s been tested, the nitrogen availability can have changed so much that your results won’t be accurate.

The best soil testing option is to use a home soil testing kit for nitrogen testing—but even those aren’t very accurate. You can definitely use them to get a general idea, though.

Growfully Protip

Lab soil tests will give you a ENR number on your report. This is the Estimated Nitrogen Release—which is the estimated amount of nitrogen that will be available to your plants based on how much organic matter is in your soil.

How do you know if your soil has too much nitrogen?

You may be thinking, “If nitrogen is so good for plants, it can’t hurt to go ahead and dump a bunch of nitrogen in before I plant, right?” Stop right there!

It IS possible for your plants to get too much of a good thing, and you don’t want your soil to have too much nitrogen. Why? Well, plants love nitrogen so much, that they can “pig out” on nitrogen. This makes for big, beautiful, lush, green plants—that don’t set any fruit at all!

Here are a few signs of too much nitrogen:

• If your plants are full and leafy and green, but you aren’t seeing much in the way of fruit set or flowers.
• If your leafy greens are bitter (and it’s not because it’s 90°F outside and your lettuce has bolted).
• If you are seeing lots of disease pressure on peas, beans, and other crops that fix nitrogen (meaning that they take nitrogen from the air and convert it into nitrogen the roots can use).

Growfully Protip

Compared to synthetic fertilizer, it can be hard to over-fertilize with organic nitrogen fertilizers. However, over-fertilizing is a real problem not to be dismissed. Runoff or leaching from excess nitrogen fertilizers can pollute water sources, help invasive species thrive, and cause community-wide health problems. Fertilize wisely!

What is the very best way to add nitrogen to my garden?

We’re going to give you lots of options in a sec for how to boost your N numbers, but if you’re looking for just one, all-around solution, we’ve got it for you. Organic matter.

Regular additions of organic matter (compost, manure, leaf mulch, straw, wood shavings, even used coffee grounds and tea bags!) will keep your garden fed with a constant supply of nitrogen as the organic matter breaks down.

The one caveat here is that nitrogen is “tied up” (meaning, not available for plants to use) in the areas where the soil is in direct contact with the organic matter as it is breaking down. So we recommend a big addition of organic matter during a time when your garden is fallow—most folks choose fall—to give the soil microorganisms time to break down and release all that nitrogen goodness.

Growfully Protip

Another way to “add” organic matter to your soil is through cover cropping (AKA: green manure). These are crops that you grow specifically for the purpose of adding nitrogen and other nutrients into the soil. You cut, mow, or till the plant matter into the soil to break down and add nitrogen and other nutrients.