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Updated: May 19, 2021

Why is nitrogen, phosphorus, and potassium so important when it comes to building soil health?

Last time, when we discussed soil health, I told you that one way soil health is measured is by how well soil produces life. The life the soil produces is of course plants.

Plants are complex beings that need water, air, and about 15 micronutrients to live, grow, and reproduce. At least two-thirds of these requirements are given to the plant through its contact with the soil. Do to the roots and what I affectionately like to call soil sludge.

But how do we as Gardeners know if the soil is giving the vegetables and fruit we wish to grow all they need?

We look at the long list of nutrients that a plant needs and see if they are in our soil. This of course can be done by conducting a professional soil test. This tests the amount of the top three nutrients needed for plant life, nitrogen, phosphorus, potassium, and a few other essential micronutrients. Nitrogen, phosphorus, and potassium are the most crucial and needed for plants to survive. I like to call them the big three.

Just a side note; these three are very important but to give a plant everything it needs you will need to try to include all 15 essential nutrients in your soil. If you'd like to learn more about these other nutrients and how to get a professional soil test done? Join my Soil Is Your Foundation Masterclass, here.

If any of these nutrients are deficient in any way, the fruits and veggies in your garden will suffer!

I'm going to look at each of these nutrients and show you why they are important and how you can add them to your soil naturally.

Remember to do a soil test first before you add anything. Learn more about my soil struggles, here!

Tall plant that have to much nitrogen


Nitrogen is essential to plant growth. In fact a sign of low nitrogen is stunted plants and too much gives you tall lanky plants. Nitrogen is needed in plans to make proteins and amino acids. Both of these are important in the development of chlorophyll. Chlorophyll is an intricate part of photosynthesis. The process in which plants produce their own food.

When looking to add nitrogen naturally to your soil it is important to know that there are three different nitrogen sources available for your veggies. The first is mineral like the natural amendments we add to our soil, the second is atmospheric, like rain. And the third is where certain plants pull nitrogen from the air and deposit it in the soil.

Using multiple sources for nitrogen will help you make a more long-lasting effect on your soil health.

Adding Nitrogen Naturally

Mineral sources are amendments that will take time to decompose in your soil before they will be available for your plants. Now just because these sources aren't a quick fix doesn't mean they should be overlooked. Building soil health takes time. These nutrients will be there to help you slowly increase nitrogen in your soil. Which will help you create a balance for both your plants and the microorganisms that live in your soil.

Natural Nitrogen Sources

Blood Meal

Advantages - it's proven to be high in nitrogen and is completely natural

Disadvantages - can attract wild animals because of the blood smell

Coffee Grounds

Advantages - a slow-release nitrogen

Disadvantages - the acid nature of unwashed coffee grounds can adjust the pH of your soil. A simple solution is just to rinse them several times before you added to a compost pile or directly to your soil.

Chicken Chicken Manure

Advantage - It is easy to find if you own chickens

Disadvantage - extremely hot! Which means very high in nitrogen so it's best to compost it first to let it let the nitrogen break down naturally before adding to the garden.

Horse Manure

Advantage - it is easy to find and is the best manure to add directly to the garden because it is not as hot as chicken manure.

Disadvantage - the horse's romun does not naturally breakdown seeds so weed pressure may increase after use. To solve this you can compost the manure first. The heat made in the process of composting should help breakdown any missed seeds.

compost is the perfect source of NPK

Alfalfa Pellets Or Alfalfa Meal

Advantage - easy to find

Disadvantages - can be on the expensive side. It would be better to buy alfalfa hay from a local farmer and compost it to break the steams down.


This would be a natural combination of the above three. Chicken manure, horse manure, as well of alfalfa pellets to increase the nitrogen in your compost pile. Also because compost itself is a great addition to your soil. It will not only increasing nitrogen but also increasing soil tilth and aeration of your soil.

Fish Poop

Advantages - can be diluted in water and applied directly to the leaves giving your plants a quick and satisfying intake of nitrogen. Tip: I use this to reduce transplant stress. I soak my transplant overnight before I transplant.

Disadvantage - it smells! You have to purchase it unless you live on a fish farm.

Atmospheric Nitrogen Sources

Nitrogen accounts for 78% of the Earth's atmosphere. Nitrogen in the air dissolves in water, creating nitric acid, which forms nitrates. The nitrates fall to the ground attached to precipitation, seep into the soil and then up into the plants. I'm not sure if you read the Farmer Boys by Laura Ingalls Wilder as a kid, but do you remember the time that the Almonzo's father plowed in about 6 in of fresh snow and called it poor man's fertilizer. This is why the snow contained nitrogen, phosphorus and a few other elements that help plants grow. Who knew! Right!

Nitrogen Fixers Sources

A nitrogen fixers a plant that pulls nitrogen from the atmosphere and traps it in itself as well as in nodules in the roots. These plants are commonly used as cover crops in backyard gardens. As a cover crop they are either harvested and placed in compost piles or used in what is called a chop and drop system. This is when a plant is allowed to grow then is chopped and dropped in place. Then left to decompose or till into the soil.

For a long list of cover crops and how to use them look here!


The second most important nutrients plants need, phosphorus, is essential for the breakdown of carbohydrates and transfer of energy in the photosynthesis process. Phosphorus can be found in organic and mineral form. Unlike nitrogen, plants can only take in phosphorus through the roots. Also a soils pH can determine the amount of phosphorus or type available in the soil

The common soil test will also tell you your pH levels. As well as your phosphorus levels and what type you have in your soil. I am sure you've heard me say it before, but getting a professional soil test done on your soil is so important!

Benefits Of Phosphorus

  • Health of plants

  • Stimulates root growth

  • Increases stem and stalk strength

  • Improves flower formation and Steve production

  • Earlier crop maturity

  • Increases nitrogen retention in legumes

  • Improves crop quality

Signs of low phosphorus are purplish leaves and weak stocks. Cooler temperatures in Spring and fall can also account for signs of low phosphorus in plants. When the soil is cooler it can not properly release the amounts of phosphorus that could already be in your soil. So it is important to look at all aspects of low phosphorus before you start throwing things at the problem hoping to get a solution.

Adding Phosphorus Naturally

Bone meal which is a natural byproduct of animals that is high in phosphorus.

Advantages - easy to find

Disadvantage - can be very expensive if a large amount of phosphorus is needed.

Rock phosphate is a naturally mind mineral

Advantage - easy to find and cheap

Disadvantage - it is a slow-release, which only means it will take time to work, remember this is not always a bad thing


Potassium is associated with the plant's ability to move water, carbohydrates, and nutrients through the plants tissues! Is also involved in enzyme activation which affects both proteins and starch production. Also is a key nutrient that helps regulate the opening closing of the stomata. Which regulates plants intake of water, oxygen, and carbon dioxide.

Benefits Of Potassium

  • Increases root growth

  • Reduces water loss and wilting

  • AIDS in photosynthesis and food formation

  • Produces respiration or energy loss

  • Enhance the sugar and starches

  • And Bill cellulose

  • Helps a plant grow stronger

  • Uses water more efficiently

  • Fights off diseases

  • Grows strong

  • Produces more

Other Aspects That Affect Potassium

Just like phosphorus other aspects affect the amount or type, and uptake of potassium

Soil Moisture

High water levels equal more available potassium

Soil Aeration

Air is needed for roots absorb the proper potassium

Soil Temperature

Plants cannot take up potassium, when the soil is too cold or too warm. Best absorption accruals between 60 to 80 degrees.


Uptake is reduced in a no-till system not sure why but could be linked to lack of are so usually using a broad fork and aerating your soil is very important!

Adding Potassium Naturally

Potassium is found in nature in three different forms. The mineral form found in mica and feldspar is completely unusable by plants. The next is potassium that is trapped between clay molecules in more clay heavy soils. This form cannot be measured in a soil test but if available will be released from the clay over time. The last form are ones that can easily dissolve into the soil sludge and help the plant survive.

Wood Ash

Advantages - Easy to find. Make sure you research different kinds of ash from different trees. Each is going to have different levels of potassium as well as different disadvantages.

Disadvantages - Will decrease soil acidity. So be aware of how much you add or the pH of your soil before you use this source. This source is usually avoid for this reason.


Advantages- Because compost is made mostly of plant material it is naturally high in potassium. It also helps the soil in many other ways so could be seen as the best for of potassium.

Disadvantage - The over use of compost can lead to an excessive amount of potassium in the soil.


Advantages - is a good source of potassium as well as a few other micronutrients. It is also known for stimulating biological activity in the soil. The liquid form is for fixing potassium deficiency quickly.

Disadvantages - the powder can be fairly expensive

Knowing how and even when to add nutrients to soil can be very overwhelming but I hope I have helped you at least understand the big three. I'm sorry I'm going to have to say it again the most important part of improving your soil is getting your soil tested. It will take you from guessing at the solution to knowing exactly what your soil needs. If you are tired of playing the amendment guessing game? And want to know what your soil needs to improve your soil’s health, grab my Free resource “4 easy steps to improving soil Health” here!

Until next time,

Pray, Just Plant


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