Like people and pets, plants need regular nourishment. Despite the replenishing properties of water and sunlight, they alone are not enough to keep our green friends growing. Enter fertilizer. The one that’s best for your plants will depend on the soil in which they’re growing and on the plants themselves. Even if they’re growing in top-notch soil, you’ll need to replace the nutrients it loses as the plants consume them. Plants have different nutrient needs at different stages of their life span (for example, nitrogen for green growth, potassium for flowering), and fertilizer containing a percentage of the big three—nitrogen, phosphorus and potassium (represented by the N-P-K ratio)—is ideal for healthy growth.