When you go shopping for npk fertilizer, you may find yourself glazing over the aisles with various varieties. You're not quite sure what kind of fertilizer for your plants need. In order to choose the best product for your plants, check the label. Most fertilizers will have three numbers on the label with dashes between each one. These numbers represent the amount of nitrogen, phosphorus, and potassium in the fertilizer. The letters NPK also appear on many packages.