How to Apply Fertilizers to Your Garden

How and When to Apply Fertilizers

Kiley Jacques
Applying Fertilizer

How do you apply fertilizers to your garden? When is the best time to fertilize vegetables and flowers? Read our tips on applying fertilizer.

5 Things to Know About Fertilizer

Consider these five points to increase the effectiveness of your applications.

  • Fertilizer is not plant food. Plants make their own food by photosynthesizing. Fertilizer provides supplemental elements that are often lacking in the soil, such as nitrogen and potassium. Think of them as vitamins.
  • Not all plants require fertilizer. If the soil in which a plant lives is rich in nutrients and the microbial life that aids in the plant’s uptake of these nutrients, then adding more can disturb that healthy ecosystem.
  • More is not better. Plants use only the nutrients that they need. To absorb more than are unnecessary can result in abnormal growth.
  • Slow is the way to go. Slow-release granular fertilizers meter out nutrients in a controlled, “digestible,” and safe manner, as opposed to fast-acting, synthetic, water-soluble fertilizers, which are, in essence, an overdose.
  • The extra cost pays off. Synthetic, water-soluble fertilizers are less expensive than slow-release products, but slow-release fertilizers don’t need to be applied nearly as often. (Plus, they don’t leach into and pollute waterways, as do many of the synthetic, water-soluble fertilizers, which plants can’t fully absorb.)

Read our article on fertilizer basics which define the NPK ratio, granular versus liquid fertilizers, and organic versus synthetic.

How to Apply Granular Fertilizers 

For the first fertilizer application of the season, apply granular fertilizers by broadcasting them either by hand or with a spreader onto the soil surface of the target plants. Using a hoe or spade fork, work the fertilizers into the top 4 to 6 inches of soil. You can also add small amounts to planting holes (be sure to mix it in with backfill soil) or to rows as you sow seeds or plant plugs. It’s a good idea to water after you have applied dry fertilizer to help it leach down toward the plants’ root zones.

During the growing season, lighter supplemental applications can be made to the top inch of soil in crop rows and perennial beds and around the drip lines of trees or shrubs. (Read the label to find out how often applications should be made.)

How to Apply Liquid Fertilizers

Fast-acting synthetic liquid fertilizers, such as Miracle-Gro, are typically applied biweekly during the growing season. High in nitrogen, which promotes fast growth and prolific blooming, they are ideal for container plantings and annuals. This type of fertilizer is typically mixed into a watering can and applied to the soil surface (rather than pouring it over the tops of plants).

Organic foliar sprays like compost tea* are rich in micronutrients and growth hormones and can be applied to vegetable crops to give them a boost. Because plants can absorb liquid fertilizers through both their roots and their leaf pores, biweekly foliar sprays are also recommended for flowering and fruiting trees and shrubs.

“Foliar feeding,” as it is sometimes called, provides plants with critical nutrients for overall good health. To apply, simply mix the liquid (according to the label instructions) in the tank of a backpack sprayer and spray all of your plants—being sure to coat the undersides of leaves, where they are more porous.

Tip: Never use a sprayer that has been used to apply herbicides. If residue from inside the tank gets onto your plants, it could be fatal.

When to Fertilize

Woody plants and perennials absorb nutrients from the soil during the growing season. They require few nutrients while dormant. Therefore, apply fertilizer as soon as the plants begin to break dormancy in the spring. Follow instructions on the label as to how often to apply (this depends on the type of fertilizer used). Stop applications after the first fall frost.

Food crops also benefit from an early-start fertilizing schedule. Some “feed” on fertilizers lightly, while others are considered heavy feeders—they require more regular applications throughout the growing season.

In general, applying granular fertilizers just before a good rain can be beneficial, as it aids in working the fertilizer down into the soil where roots can access it. In the case of liquid foliar sprays, it is best to apply them on dry days in either the early morning or the early evening when the leaves will have time to absorb the material. Avoid extremely hot days when foliage is subject to burning.

* Here’s more information about how to make compost tea.

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