Walk into any garden center and you’ll see fertilizer bags with numbers such as 10-10-10, 20-5-10, 5-10-10, etc. To many gardeners, those numbers look like some kind of secret code…they’re not.

Those three numbers represent the three primary nutrients that every one of your vegetable plants and fruit trees needs to grow and produce, with a few rare exceptions.

The nutrients represented by those numbers are N-P-K…and that translates to:

• N = Nitrogen
• P = Phosphorus
• K = Potassium

Plants need many other nutrients too — calcium, magnesium, sulfur, iron, zinc, and others — but N-P-K forms the basic foundation that most fertilizers are built around. For now, think of N-P-K as the three primary nutrients plants use for growth. Regardless of where they originate, plants absorb them as chemical nutrients dissolved in the soil.

Look at a plant this way…

What they do –

Nitrogen (N): Builds leaves and overall plant growth. Nitrogen mainly provides green leafy & stem growth, overall plant vigor, and chlorophyll production.

Chlorophyll is essentially the plant’s solar panel system. It’s the green pigment inside plant cells that captures sunlight and converts that light energy into usable energy. Chlorophyll is why most plants are green. It reflects green light and absorbs much of the red and blue light.

If you want lush green plants, nitrogen is heavily involved.

Phosphorus (P): The root builder and flower & fruit motivator. Phosphorus helps support root development, flower formation, fruit development, and the transfer of energy inside the plant.

Young transplants especially benefit from (i.e. need) adequate phosphorus because roots are being established.

Potassium (K): Kinda like the overall plant health manager. Potassium helps regulate a whole bunch of internal plant functions such as water movement, disease resistance, stress tolerance, fruit quality, and overall plant strength.

Think of potassium as the plant’s maintenance and support system. Plants with adequate potassium often show better tolerance to heat and drought stress, greater disease resistance, and improved tolerance to temperature swings.

Fertilizer Numbers –

Suppose a fertilizer bag says 10-10-10, that means it contains:

• 10% Nitrogen
• 10% Phosphorus
• 10% Potassium

If a fertilizer bag says 20-5-10, that means it contains higher nitrogen, lower phosphorus, and moderate potassium. For you number obsessed folks:

• 20% Nitrogen
• 5% Phosphorus
• 10% Potassium

How the numbers lay out –

The N-P-K numbers are percentages by weight. So a fertilizer labeled “10-10-10” means:

• 10% Nitrogen by weight
• 10% Phosphorus by weight
• 10% Potassium by weight
• 70% is other material (carriers, fillers, secondary nutrients, trace minerals, coatings, etc.)

Real-life example…a 10-lb bag of 10-10-10 contains approximately:

• 1 lb Nitrogen
• 1 lb Phosphorus
• 1 lb Potassium
• 7 lbs other ingredients

How fertilizer is used –

Leafy vegetables often benefit from more nitrogen. Tomatoes and peppers usually benefit from somewhat less nitrogen once flowering and fruiting begin. Fruit trees like/need balanced nutrition, but excessive nitrogen can produce leaves and branches at the expense of fruit.

Generally speaking…

The big mistake many gardeners, like myself, make or have made is…More fertilizer does not automatically mean healthier & stronger plants and more fruit production.

Too much fertilizer can:

• Burn roots
• Cause excessive leaf growth
• Reduce flowering
• Reduce fruit production
• Create nutrient imbalances

Plants are a little like people…more food isn’t always better. The right food at the right time for the right reason matters more than the volume of food.

Side Note –

Are you wondering why I am not promoting organic fertilizers? Well, that wasn’t the point to this article. I am simply trying to explain the N-P-K fertilizer concept and what each chemical element provides to plants and fruit trees.

Plants absorb nutrients as dissolved chemical elements in soil water. Once nutrients become available for uptake, the plant generally does not distinguish whether those nutrients originally came from an organic source or a synthetic source. Small differences can exist in how fast nutrients become available, how long they last, or what other compounds come along with them, but the nutrient itself that crosses into the root is the same absorbable form.

Let me restate that…The plant does not care whether the nutrient originally came from an organic source or a synthetic source once the nutrient reaches the form the plant can absorb.

The plant does not have a mechanism that says, “This nitrogen came from compost, I like that one.” Or, “This potassium came from a factory, reject it.” The plant only sees the absorbable nutrient in the soil solution.

Relax…I will get to the organic vs synthetic fertilizers in the next article. And yes, I advocate organic fertilizers over synthetic fertilizers…more on that later.

 

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