10 Easy Ways to Add Nitrogen to Your Soil

Nitrogen, a key macronutrient for plants, is vital because it is a major component of chlorophyll, the compound that lets plants perform photosynthesis. Nitrogen is also a major component of amino acids. Without these building blocks of proteins, plants would wither and die. Therefore, it is crucial to know how to add nitrogen to soil to supply your plants, whether they're ornamentals or edibles.

However, not all nitrogen is the same. This overview of nitrogen sources and products helps you pick the nitrogen that works best for what you grow. Unless otherwise noted, for amounts, follow the instructions on the product label.

How to Tell if Your Soil Needs Nitrogen

Before adding nitrogen—or any other plant nutrient, for that matter—you need to be sure that the plant really lacks it. Excess nitrogen is not only bad for plants but also for the environment, as nitrogen runoff pollutes waterways and other bodies of water. If you are dealing with a large area such as a vegetable garden, the best way to make sure nitrogen is needed is to do a soil test. For individual plants, that’s not always practical and feasible. Still, before you give an unhealthy-looking plant a nitrogen boost, make sure to rule out other causes.

Physical signs your soil needs nitrogen include chlorosis (yellowing leaves), lack of flower bloom, fruit not producing, recurring disease, or overall failure to thrive.

Manure

All manure contains nitrogen, in addition to the two other macronutrients phosphorus and potassium, but there are significant differences in the type of manure. Chicken manure has the most nitrogen, followed by horse manure and cow manure.

Fresh manure needs to be composted or rotted for at least six months to a year before you can use it in the landscape or garden. If you don’t have access to fresh manure, or won’t be able to let it sit, you can buy aged manure in bags from a garden center. For 100 square feet, use 200 pounds of cow manure, 70 pounds of chicken manure, or 65 pounds horse manure. The best time to add manure is in the fall. 

Biosolids

Biosolids are organic materials that have been recycled from municipal wastewater treatment plants. The two types of biosolids from wastewater treatment that are offered for garden or landscape use are heat-dried products and Class A blends, which are mixed with sand, sawdust, and bark. Both types have been processed with heat to destroy pathogens. Class A follows the highest standard of pathogen removal for biosolids and trace element pollutant levels. However, be aware that biosolids, which are commonly sold as “recycled nutrients” in large bags, may contain toxic chemicals known as PFAS.

Compost Tea

If you are composting in your backyard, you can steep or brew the vermicompost in water to make homemade nitrogen fertilizer for your plants. Producing compost tea works best on a small scale, such as for container plants. But it does not free you from having to give your plants additional nutrients; it’s best used as a quick and easy fix when you don’t have commercial fertilizer on hand. 

Animal Products

Fish emulsion, or fish fertilizer, is a nitrogen fertilizer made from by-products of the fish oil and fish meal industry. It is quick-acting yet the drawback is its repugnant fishy odor.

Blood meal is a by-product from slaughtering cows and other animals. It is dried into a powder and sold in bags. Dogs are attracted to blood meal, so work it and water into the soil if Fido is around.

Guano is the accumulated excrement of seabirds or bats. 

Nitrogen-Fixing Plants

One of the most natural ways to increase nitrogen in the soil is to plant nitrogen-fixing plants— members of the legume family, such as peas, beans, or cover crops (clover, vetch, and alfalfa). The roots of the plants are colonized by bacteria that extract nitrogen from the air and turn it into nitrogen that is required for bacterial growth. Once the bacteria don’t need the nitrogen any longer, it becomes available to the plants. Tilling the cover crop under adds additional nitrogen to the soil. 

Commercial Fertilizer

Balanced or complete fertilizers contain the three macronutrients nitrogen, phosphorus, and potassium. For a high-nitrogen fertilizer, select a product where the first number is the highest. Most fertilizers consist of a blend of nitrogen sources that are both quick-release and slow-release to ensure a speedy greening and a longer effect. Just like the N-P-K ratio or percentage, the nitrogen source ratio or percentage is listed on the product label. 

Inorganic Sources of Nitrogen

Nitrogen from inorganic mineral sources includes ammonium nitrate (33.5% nitrogen), calcium nitrate (15.5% nitrogen), and ammonium sulfate (20.5% nitrogen). These pure nitrogen fertilizers are mostly used for lawns and turfgrass and usually labeled as such. All are water-soluble so they are immediately available to the plant upon watering. While this yields fast results, it also bears the risk of burning the plant if too much nitrogen is applied, which also causes nitrates to leach into the soil. 

Synthetic Nitrogen

Synthetic nitrogen comes primarily in the form of urea or urea solutions for lawn and turf applications. On its own, urea is a quick-release nitrogen fertilizer. Urea is also combined with other substances, or a coating is added to make it a slow-release fertilizer. How fast coated urea releases nitrogen to the soil depends on the thickness of the coating, temperature, and soil moisture.

Grass Clippings

Did you know grass clippings are high in nitrogen? When they break down, they help to release nitrogen into the soil. This is an easy and cost-effective way to boost your plant's nitrogen. Simply lay them as a mulch layer around your plants.

Coffee Grounds

Coffee grounds add nitrogen to soil, but there’s a caveat. If you are incorporating coffee grounds directly into the soil, you also need to add a nitrogen fertilizer. The microorganisms that break down the coffee grounds in the soil use nitrogen for their growth and reproduction, which means they are taking away nitrogen from the plants. To make sure that the plants get enough nitrogen during the decomposition process, additional nitrogen in the fertilizer gives your plants the nutrient they need.