Understanding Garden Fertilizer: What does 10-15-20 mean?

Gardening leads to fertilizing. The basics... Fertilizer is broken down into 2 categories. Macronutrients and Micronutrients. You are most familiar with the Macronutrient numbers. A bag of fertilizer may read 10-15-20 and that represents the amount of Macronutrients in the product. In order- it is Nitrogen, Phosphorus and Potassium. Or using the example of 10-15-20: Nitrogen 10 Phosphorus 15 and Potassium 20. For gardening I recommend a 10-10-10 fertilizer. It keeps things simple. These are the three primary Macronutrients.

The other three Macronutrients are the secondary nutrients or Sulfur, Calcium and Magnesium. These may or may not be in the fertilizer you purchase.

The Micronutrients are known as trace elements such as boron, copper, zinc and iron. These typically don't come in your basic bag of 10-10-10 fertilizer. Or if the they do, they are in trace amounts. Check the packaging for details.

There are two types of fertilizer. Soil and foliar. Soil fertilizer is typically the granules that come in 40 pound bags. And foliar is more like Miracle Grow you mix with water.

That's the basics.