BiotiQuest® Gut Health & Probiotics Blog with Martha Carlin

A Simple Guide To Adding Nitrogen In a Garden

Martha Carlin | May 29, 2024 |

For seasoned gardeners and newbies alike, maintaining soil health is an essential step towards a bountiful harvest. Ensuring that your garden soil is rich in essential plant nutrients like nitrogen, phosphorus, potassium, and trace minerals can be the difference between a lush vegetable garden and a scraggly one.

Nitrogen is one of the key contributors to plant health, and despite its abundance in the atmosphere, it can be tricky to make it available to your plants. If you're wondering about how you can add nitrogen to your garden soil, let's dive right in!

Atmospheric nitrogen vs. soil nitrogen

Even though the atmosphere contains up to 78% nitrogen gas, plants cannot easily use it in its gaseous form. Nitrogen-fixing bacteria and nitrogen-fixing plants work in symbiosis to attract and fix atmospheric nitrogen in the soil. In this way, nitrogen-fixing plants and bacteria not only fulfill their own nitrogen needs but also make it available to surrounding plants.

Simultaneously, already fixed nitrogen in plant and animal molecules such as amino acids (protein building blocks) can be recycled back into your garden soil in the form of manure, compost, and plant waste (straw, leaves, sawdust).

What affects nitrogen levels in garden soil

Factors like soil pH and moisture content influence both soil structure and soil fertility and dictate how much nitrogen your garden soil retains and makes available for plant growth.

Soil pH

Soil pH refers to the acidity or alkalinity of your garden soil. Most plants thrive within soil pH ranging between 6 and 7.5 as most nutrients are available for absorption in this range.

When your garden soil is either too acidic (pH lower than 6) or too alkaline (pH higher than 7), primary and trace nutrients become less available to plants, including nitrogen. Highly acidic soils can have low microbial activity that leaves nitrogen trapped in organic matter and unavailable to plants, whereas nitrogen in alkaline soils is trapped in chemical compounds that cannot be utilized by plants.


Heavy rainfalls or over-watering can adversely affect nitrogen availability in the soil. Excessive moisture can lead to nutrients leaching off to lower levels that cannot be accessed by plant roots. Highly saturated soils also allow fixed or applied nitrogen (compost, fertilizer) to get converted back to nitrogen gas (denitrification) allowing it to escape back to the atmosphere.

Like everything else in life, there are exceptions to these gardening rules. Berries such as cranberries and blueberries and root vegetables such as radishes like slightly acidic soils, whereas citrus, fig, and pomegranate trees can thrive in slightly alkaline soils.

What does nitrogen deficiency look like?

By the time nitrogen deficiency becomes visible in plants, your plant has already been struggling for a while. Nitrogen is essential for chlorophyll synthesis, a green pigment that helps convert sunlight and carbon dioxide into energy and oxygen.

Nitrogen deficiency limits chlorophyll synthesis, limiting photosynthesis, and leads to pale green or yellowing leaves, stunted growth — limited branching, flowering, and fewer and smaller fruit. 

So, how can you add nitrogen to your garden soil?

Organic ways to add nitrogen and improve soil health

There are two approaches to how you might want to handle soil health in your garden: long-term gains and short-term fixes. Crop rotation and nitrogen-fixing plants can ensure plentiful nitrogen for the next batch of crops and by adding mature animal manure and compost to your garden, you’re ensuring its long-term health. 

Crop rotation and nitrogen-fixing plants

Different types of plants utilize different nutrients during their growth cycles. Generally, root vegetables require more potassium, the development of fruits requires more phosphorus, legumes synthesize their own nitrogen, and green leafy veggies rely on more nitrogen than most.

Nitrogen-fixing bacteria live in the roots of nitrogen-fixing plants and form nodules that convert atmospheric nitrogen into ammonia. These plants use ammonia to grow and release it into surrounding soil as their roots decompose. 

Rotating plants that have different nutrient needs will prevent your garden soil from getting deficient in any single nutrient. Planting and harvesting nitrogen-fixing plants before planting brassicas like cabbage, cauliflower, bok choy, and Brussels sprouts can be a great way to add nitrogen to soil and improve soil structure.

Beans and legumes like broad beans, green beans, peas, and chickpeas, as well as cover crops like alfalfa and clover, are a few examples of nitrogen-fixing plants that can be great additions to your vegetable garden.

Another way to enhance soil fertility and nitrogen availability in the soil by fortifying your garden soil with Yield and Shield. Yield and Shield’s carefully selected microbial guild includes nitrogen fixing microbes that can boost nitrogen fixing activity of your garden soil.

Composted manure

Adding compost improves both nutrient availability and nutrient holding capacity (cation exchange capacity) of the soil. Completely composted animal manure can be a boon to your garden soil. A great source of nitrogen and several other nutrients, animal manure also enhances the soil microbiome, which further improves soil structure in the long run.


When adding animal manure to your garden soil, make sure to add only well-composted manure, since fresh or partially composted manure can potentially burn your plants. Fresh manure can also introduce pests to your garden. You can use composted animal manure like: 

  • Rabbit manure
  • Chicken manure
  • Sheep manure
  • Cow manure
  • Horse manure

One more factor to consider when obtaining manure is its origin. Manure from grain-fed poultry and cows has probably been exposed to herbicides and can impact the soil’s microbiome. Poultry and cow manure in particular should come from free range, grass fed animals and not grain fed. Ensure that the fields have not been sprayed with broadleaf herbicides.


Vermicompost is waste produced by earthworms while breaking down organic material (food scraps, coconut coir, cardboard, straw, or hay). It’s one of the healthiest soil amendments you can add to your garden soil, as it contains a balanced mix of all primary nutrients and improves soil structure by enhancing water retention and aeration of the soil.


Vegetable and garden compost

Composting kitchen waste is one of the easiest and cheapest ways to maintain the health of your garden soil. Coffee grounds, tea leaves, eggshells, grass clippings, vegetable, and fruit peels are excellent additions to your growing compost pile. 

Few quick and easy ways to add nitrogen to garden soil

Short-term fixes including diluted compost tea and vegetable peel tea, worm castings (contains only worm waste which is slightly different from vermicompost), feather meal, bone meal, fish emulsion, blood meal, alfalfa meal, diluted human urine and fruit peel powders can all provide a quick boost to your vegetable garden soil.

Citrus fruit peels and banana peels are especially rich in nitrogen and micronutrients. 

In a jar cut up available fruit peels into small pieces, add about a liter of water, loosely cover, and let it ferment for about a week. Strain the tea and dilute it in a 1 to 10 ratio with water, and your fruit peel tea is ready for use.

Some fruit and vegetable peels you can use to make fruit and vegetable peel teas are:

  • Citrus fruit peels from oranges, lemons, and grapefruit for nitrogen.
  • Potato, onion, and garlic peel tea (Garlic and onion peel tea also makes for an easy homemade pesticide).
  • Bananas, pomegranate, apple, mango, and guava peels for phosphorus and potassium.

When and how much nitrogen does your vegetable garden need?

Depending on your plant variety and soil organic matter, your vegetable garden may need nitrogen anywhere from 8 ounces to 2-4 lb per 1000 sq ft at the beginning of a growing season (roughly three weeks before planting).

Vegetable gardens with heavy feeders such as asparagus, broccoli, celery, corn, eggplant, melons, pumpkins, and tomatoes, etc. require a lot more nitrogen than light feeders (herbs, radishes, spinach) or nitrogen-fixing plants like peas and beans.


Here are a few things to consider while choosing your preferred form of nitrogen soil amendment for your vegetable garden:

  • Consider getting your garden soil tested. A soil test can make it easy for you to preplan which soil amendments you wish to add to your soil, at what quantities, and at the appropriate time. Or, if you’re into DIY, you can test your garden soil pH at home.
  • If, according to the soil test, soil nitrogen is around 40 ppm (parts per million) then you don't need to add nitrogen at the beginning of the season but will likely need to supplement it as the growing season progresses.
  • If, according to the soil test, soil nitrogen is higher than 40 ppm at the beginning of the growing season, then you may not need to supplement your garden soil at all that season.
  • Similarly, if soil organic matter in your garden is at 5% then you won't need to add more nitrogen at the beginning of the season.
  • There's no need to add nitrogen to the soil when planting nitrogen-fixing plants like legumes and beans, as they fulfill their nitrogen needs from atmospheric nitrogen.

Can you have too much nitrogen in garden soil?

It isn't just us humans who love to overeat and when plants do it, it's called luxury consumption. Too much nitrogen in the garden can lead to dense foliage, compromising airflow that might lead to disease.

Additionally, when a plant uptakes more nitrogen than it may need, its focus shifts to rapid growth over flowering and fruiting, affecting yield.

Building healthy soil with organic compost and soil probiotics

Soil structure is a defining factor when it comes to the overall health of your vegetable garden, which in turn is highly dependent on the soil microbiome. The soil microbiome impacts how well the soil holds onto nutrients, if and when nutrients become available for plant uptake, and ensures there’s optimum water retention and aeration. 

If you're seeing signs of nitrogen deficiency in your plants like yellowing leaves or stunted growth or plan to grow heavy feeders in the upcoming season, consider amending your garden soil with organic nutrient sources like vermicompost and animal manure. In addition to adding organic matter back into your soil, organic composts also inject much-needed microorganisms into the soil.

Side view of Yield and Shild 8 ounce fluid container.Soil microorganisms share a symbiotic relationship with plants, recycling nutrients and keeping pathogens at bay. The presence of soil probiotics can help your garden hold on to nitrogen that might otherwise leach off or turn to nitrogen gas. 

Let Yield and Shield’s carefully selected microbial guild bring new life to soil that’s been treated with herbicides and pesticides in the past, store bought garden soil (often contaminated) or quite simply to prep your garden soil before you begin planting to help you enhance nitrogen uptake, break down stubborn glyphosate residue, and rejuvenate your garden soil.

Fortify your garden soil with Yield and Shieldand enjoy a bountiful harvest! 

With gratitude,

Martha Carlin photo Martha Carlin, is a “Citizen Scientist”, systems thinker, wife of Parkinson’s warrior, John Carlin, and founder of The BioCollective , a microbiome company expanding the reach of science and BiotiQuest, the first of it’s kind probiotic line. Since John’s diagnosis in 2002, Martha began learning the science of agriculture, nutrition, environment, infectious disease, Parkinson’s pathology and much more. In 2014, when the first research was published showing a connection between the gut bacteria and the two phenotypes of Parkinson’s, Martha quit her former career as a business turnaround expert and founded The BioCollective to accelerate the discovery of the impact of gut health on all human disease. Martha was a speaker at the White House 2016 Microbiome Initiative launch, challenging the scientific community to “think in a broader context”. Her systems thinking background and experience has led to collaborations across the scientific spectrum from neuroscience to engineering to infectious disease. She is a respected out of the box problem solver in the microbiome field and brings a unique perspective to helping others understand the connections from the soil to the food to our guts and our brains.

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