Choose the right fertilizer
Understanding the meaning of the three numbers printed on the packaging will give you an edge in choosing which fertilizer is right for your plants. The illustrations on this page represent common examples, but the numbers will vary from product to product. What you're looking for is the ratio of nitrogen to phosphorus to potassium (N-P-K).
High Nitrogen Fertilizers for Leaf and Stem Growth
If the first number is higher than the other two, you're looking at a high-nitrogen fertilizer. High-nitrogen feeding is ideal for building up young vegetable plants until they're strong enough to support fruit, and for the health and growth of leafy greens and herbs you don't want to go to seed. Additionally, feeding high nitrogen to your onions will encourage layer growth and nice, plump bulbs.
High Phosphorus Fertilizers for Flowers and Fruit
The middle number in the N-P-K ratio represents phosphorus. Fertilizers showing a high middle number are recommended to promote flowering and fruiting. In your vegetable gardens, feed this to your fruiting veggies, such as tomatoes, peppers, and squash, once the plants are strong enough to support fruit. Your flower gardens will also appreciate the high-phosphorus fertilizer.
High Potassium for Plant Functionality and Metabolism
Potassium-rich fertilizers make an excellent soil supplement for gardens, lawns, and crops. Potassium has been shown to help streamline the movement of water and nutrients through plant systems, increase resistance to stress, and contribute to root growth and chlorophyll production. For root vegetables like beets and carrots, look for an N-P-K ratio richer in potassium and phosphorus than nitrogen, such as 5-10-10.
All-purpose fertilizers have equal proportions of nitrogen, phosphorus, and potassium, and are recommended in situations where the soil is nutrient-poor. For example, a houseplant that has been living and feeding from the same potted soil for most of its life needs to be fed in order to thrive and grow.
Some fertilizers with an exaggeratedly high middle number are meant only to supercharge blooming in annuals, and do not qualify as a healthy diet for your perennials, herbs, vegetables, shrubs, trees, or grasses. Use these on your flowering annuals in hanging baskets, planters, and pots for glorious color all season long.