When to fertilize
To get your plants off to a good start, fertilize when the spring growing season begins. Many gardeners use a general-purpose fertilizer at this time (either an evenly balanced formulation or one slightly higher in nitrogen); others add only nitrogen. How often you fertilize later in the year depends on the plant. Nutritional needs differ, so it's important to check the particular requirements of the plants you buy; for general guidelines on bulbs, lawns, annuals, and many other kinds of plants, go to our Plant guide..
Some plants are heavy feeders and benefit from regular applications of general-purpose fertilizers and extra nitrogen throughout the growing season. Others ― often those that evolved in nutrient-poor environments ― may need only one annual feeding with a general-purpose fertilizer (or they may flourish with no feeding at all).
Tip: Don't apply liquid fertilizer at the same time you plant. No matter how carefully you remove plants from their containers and place them in the ground, some root hairs will break. The fertilizer will reach the roots immediately and enter them at the broken points, "burning" them and causing further dieback. Wait 2 to 3 weeks after planting before you fertilize; by then, the newly set-out plants should have recovered from any root damage.
Use a spading fork to work a dry granular fertilizer into a new garden bed. This technique puts phosphorus and potassium at the level where they can best be absorbed by plant roots. Water thoroughly after incorporating the fertilizer.
Using a cultivator, gently scratch the soil beneath plants with roots growing close to the surface. Apply a dry granular fertilizer and water thoroughly. Because roots may extend several feet beyond the drip line, be sure to spread fertilizer out wide enough to reach all the roots.
Liquid fertilizers can be applied with a watering can. You can also use an injector device to run the fertilizer through your watering system. A simple siphon attachment (above) draws a measured amount of fertilizer into a hose from concentrate in a pail.