How to Understand Fertilizers

Video by Jonathan Parrish

Fertilizing your lawn and garden is an important maintenance step that shouldn’t be overlooked. Fertilizer helps plants get established, keeps plants healthy, and encourages growth. But with so many different types of fertilizers and ratios, knowing which kind to use can be confusing.

Before we get into the basics, the first and most important thing to do before fertilizing is taking a soil sample from your yard or garden. Soil samples are an easy and helpful way to find out exactly how much and what type of fertilizer you need. Our blog post on how to take a soil sample gives you all the details you’ll need on this process. 

When looking at fertilizer packaging, you’ll notice three sets of numbers. Don’t let these numbers overwhelm you! They simply represent the amount of nitrogen (N), phosphorus (P), and potassium (K) in the fertilizer’s formula. For example, a bag that has 7-22-8 written on it has 7 percent N, 22 percent P, and 8 percent K. The numbers will always be presented in the N-P-K ratio. Complete fertilizers have different ratio numbers, while balanced fertilizers contain the same ratios. The results of your soil sample test will tell you which ratio you’ll need to purchase. 

There are several different types of fertilizers on the market to choose from. Here’s a quick rundown of the terms you’re likely to see on fertilizer bags:

• Controlled vs. slow-release:  Don’t let these terms confused you! They actually mean the same thing and the terms are often used interchangeably. Controlled and slow-release fertilizers have a coating around the nutrients that allow them to release over time. 
• Organic vs. synthetic: Organic fertilizers are natural and release the nutrients slowly by breaking down the potting mix. Synthetic fertilizers offer a quick fix of nutrients for your plants and are not naturally derived. Check out this awesome visual on the difference between organic and synthetic fertilizers!
• Granular vs. water-soluble: Granular fertilizers can be made from both organic and inorganic sources and contain readily water-soluble nutrients. Water-soluble fertilizers need to be mixed with water before applying to plants.

If you need help understanding your test results or need advice on which product to buy, reach out to your local Extension office.