Role of Nitrogen in the Garden & How to Add Nitrogen to Soil

Soil Nutrients

We all know that nutrients are essential to life for humans, animals, and plants. Whether it is nitrogen or other essential nutrients such as phosphorus, calcium, potassium, magnesium and sulfur, understanding the nutrients each plant needs and when they actually need them is vital for successful gardening! 

The Role of Nitrogen In The Garden

Nitrogen is a building block of life, a naturally occurring chemical element. It is one of the big 3 macro-nutrients responsible for growth, and associated with green leaves and healthy plants. Nitrogen is used in the leaf to produce chlorophyll, which is a form of energy that is created from absorbing sun rays.  

Nitrogen also helps to produce healthy seeds and fruit. Without nitrogen, plants will look skinny and anemic, become stunted, and begin to yellow. The first symptom of a nitrogen deficiency is often yellowing of the lower leaves. (Here’s more on what causes vegetable leaves to turn color.)

Nitrogen Cycle Diagram

The nitrogen cycle is a continual natural process through which nitrogen circulates between the atmosphere, soil, water, and living organisms. Because they cannot use nitrogen gas directly from the air, plants count on other sources to create a link in the nitrogen cycle. 

Soil microorganisms, such as nitrifying bacteria, often complete that link by converting atmospheric nitrogen. These nitrogen-fixing bacteria in the soil cling to plant roots and absorb nitrogen from the air, and convert it into nitrate, a soluble form of nitrogen that plants can use. 

Organic matter also adds nitrogen to the soil. When a once-living organism begins to decay or decompose (a.k.a. compost), it forms a substance called ammonium. The nitrifying bacteria consume ammonium and convert it into nitrate (NO3)! 

Soil Testing For Nitrogen

Before adding nitrogen to soil, it’s a good idea to test your soil first to determine how much nitrogen it actually needs! I recommend using the Rapitest Soil Test Kit because it is a really well-rounded test that you don’t have to pay an arm and a leg for. 

It has 40 tests-10 for each pH, nitrogen, phosphorus and potassium. So you don’t just get to test once, but 39 more times! 

If you want to go really in depth, you can get your soil tested for micronutrients, but it is expensive. And honestly, when you look at a garden that is growing poorly, chances are the small things aren't the problem. It is likely that the three main macronutrients or soil pH are the problem. Once you get the big things dialed in, then the small things can become important.

How to Add Nitrogen to Soil

If your soil is low in nitrogen, here’s the good news: there are lots of ways to add nitrogen to soil!

1. Apply Commercial Fertilizer - The most common method to add nitrogen to soil is to apply fertilizer. We at MIgardener wanted a better fertilizer that would benefit our gardens and help us Grow Bigger, so we developed Trifecta+ fertilizer and Revive Rx liquid fertilizer. These soil superchargers are rich in fast-acting nutrients, trace minerals, and more!

2. Amend With Compost - Amending garden soil with finished compost is a great way to boost nitrogen. Read this blog post to learn how to make compost easily.

3. Plant Cover Crops - Cover crops are soil-saving superstars that protect bare soil, improve fertility, enhance soil structure, prevent erosion, and some will even “fix” nitrogen into the soil. 

4. Amend With Manure - Rabbit, cow, horse, goat, sheep, and chicken manure are VERY high in nitrogen and can range from 4% to 9% nitrogen by weight. Pro-Tip: It is better to compost manure before adding it directly to garden soil to prevent “burning” plants (giving them a too-high nitrogen concentration).

5. Add Blood Meal - Amending with blood meal is a great way to add nitrogen to your soil and improve soil structure! 

6. Use Grass clippings - When composted, grass contains about 3% nitrogen by weight.

7. Human Urine - As gross as it may seem, human urine and biosoilds are an extremely reliable form of nitrogen, and also contain other beneficial trace minerals that help plant growth. Urine should be diluted 5 parts water to 1 part urine to prevent burning. (Watch this video to learn more about biosolids as fertilizer.) 

8. Homemade Fertilizer - These tutorials will teach you how to make (and use) my favorite effective homemade fertilizers: How to Make Compost, How to Make Compost Tea, How to Make Bone Meal Fertilizer, How to Make Seaweed Fertilizer, Vermicomposting, and even How to Make Fertilizer Out of Pumpkins!

Pro-Tip: When you look at a bag of fertilizer, you'll see the NPK labeled as three numbers. NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K), the three predominate macronutrients needed by plants. The first number in that label represents the guaranteed percentage of nitrogen, by weight, of that fertilizer. After a soil test, follow the instructions to fertilize the correct amount and frequency.

Too Much Nitrogen

Too much of a good thing can be a bad thing! In other words, nitrogen can be used in excess and do more harm to your plants than good.

Over-fertilizing with nitrogen causes fertilizer burn.This will actually weaken and stress the plant, which invites pests and diseases. Over-fertilizing is also a common cause of delayed flowering and fruiting.