Fertilizer by the Numbers: Which Fertilizer Should You Choose?

Whenever you buy fertilizer from your local landscape supply store, you will notice that there are three numbers prominently listed on the packaging. You can typically find them on the front, formatted like “xx-xx-xx,” and they can tell you a great deal about what the fertilizer will do for your lawn and garden.

Spoiler alert: The numbers refer to Nitrogen, Phosphorus, and Potassium (N,P,K), and they are always listed in this order. The numbers represent the percentage within that package of each component.

For example, a common type of all-purpose fertilizer is referred to as 10-10-10. This is a balanced blend of equal portions of Nitrogen, Phosphorus, and Potassium. If you purchased a 50-pound bag, five pounds (or 10%) would be Nitrogen, five pounds would be phosphorus, and five pounds would be potassium. The remaining 70% is simply filler, or inert ingredients, which are there mostly to help disperse the chemicals when you spread them.

Up, Down, and all Around

A common way of describing the purpose behind each chemical is to think “up, down, and all around.”


Applying this simple phrase will help you remember that Nitrogen (N), the first chemical listed, helps with plant growth above ground. Nitrogen does a great job of promoting the green leafy growth of foliage, while providing the necessary ingredients to produce lush green lawns. Lawn fertilizers will frequently have a high first number for this purpose.


Phosphorus (P), the middle number, is very effective at establishing growth below ground, in the form of healthy root systems. It is also the component most responsible for flower blooms and fruit production.

You’ll notice that fertilizers designed for flower production, or starter-type fertilizers for your lawn, have a high middle number.


Potassium (K), the last number listed, is considered important for overall plant health. This is primarily due to its ability to help build strong cells within the plant tissue. In turn, the plants withstand various stresses, such as heat, cold, pests, and diseases.

Potassium is an essential plant nutrient and is required in large amounts for proper growth and reproduction of plants. Potassium is considered second only to nitrogen, when it comes to nutrients needed by plants, and is commonly considered as the “quality nutrient.”

In addition, potassium helps with the regulation of water that flows properly to your plants, so it’s an important energy source for many chemical processes taking place.

Why Does This Matter?

When shopping for fertilizers, be mindful of their intended use. Fertilizers that have equal numbers can generally be used as an all-purpose fertilizer. If you had only one product to work with, 10-10-10 would be a smart recommendation.

For promoting good plant and flower production, look for a middle number that is higher than the first. Otherwise, your plants will be stimulated to put out lots of nice green foliage, likely at the expense of flower production.


Instead, you want the energy and nutrition of the plant to go towards the desired result, like your flowers, so a higher middle number is a more appropriate choice.

To toughen up your plants or lawn for environmental stresses, you’ll want a fertilizer that promotes the last number, and middle number. A high first number in this case may not be appropriate, because you are not likely to be promoting new lush foliage when at the same time putting plants or turf to bed for the winter. Instead, your goal should be to promote cell structure and strong roots which continue to grow through winter.

Finally, whenever you apply fertilizers, don’t assume that more is better. You can burn plants by over fertilizing, and damage the surrounding soil as well.

Instead, opt for the practice of less is better. If your soil is rich in organic matter, it should have all the nutrition that your plants need.

Beautiful lawns and gardens start with healthy, well-nourished plants. From grasses to flowering shrubs, every plant’s need is different, but some basics apply across the board.

Choosing the right fertilizers for your lawn and garden doesn’t have to be difficult. Armed with these fertilizer basics, making the right choice is as simple as 1-2-3.

By understanding the basics behind fertilizer labels, you can choose the right products for your lawn and garden goals with confidence. Big Earth Supply’s selection of lawn and garden fertilizers can help your lawn and garden reach its full potential for beauty and enjoyment.

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