How to Fertilize a Garden Bed

Learn how to effectively fertilize your garden bed to encourage beautiful, healthy flowers, and vibrant foliage that will make your garden stand out! A beautiful garden with blooming flowers and vibrant colors can enhance your backyard. Whether you're growing beginner-friendly flowers, selecting perennial plants that bloom every year, or planting flowering plants that attract pollinators, taking good care of your garden is essential.

By following the best watering practices, timely weed removal, and applying the right flower fertilizer, you will encourage your plants to produce stunning flowers and colorful leaves. It can even help them thrive during summer heatwaves. Learn how to fertilize your garden bed and enjoy breathtaking flowers in your garden!

What You'll Need

Before fertilizing, gather some essential items to make amending your garden bed a breeze.

Measuring tape (to determine the size of the garden bed)

Organic compost, well-aged manure, or leaf mold

Synthetic fertilizer (granular or liquid)

Organic alternatives (coffee grounds, eggshells, or Epsom salt)

Research Your Flowers

The first step in fertilizing your garden bed correctly is to research your flowers. There are various types, and not all flowers require the same type of fertilizer.

Perennials vs. Annuals

First, determine if you have perennial plants or annuals (perennials regrow every year, unlike annuals that need to be replanted each year). In terms of fertilizing, perennials typically only need an application of 1 to 2 inches of organic material once a year in spring. In contrast, annuals usually benefit from balanced fertilizers twice a year. First in spring, and again in midsummer, around July or after flowering occurs.

There Are Many Exceptions

However, even within similar types of flowers, such as perennials and annuals or cultivated varieties, the type, timing, and frequency of fertilization can vary. For example, some annuals prefer balanced fertilizers every two to three weeks or once a month, such as marigolds. Then, other annuals, like petunias, might only need a single application of general-purpose fertilizer in spring, while zinnias, another annual, don't like any fertilizer at all.

Perennials can also vary. For instance, daylilies enjoy a spring application of 1 to 2 inches of organic compost, followed by balanced fertilizer after they bloom in midsummer, or you can use slow-release 20-5-10 fertilizer just once in spring. Then, tall bearded irises benefit from 1 to 2 inches of organic material in spring and when they bloom, or a 10-10-10 fertilizer. Mums, on the other hand, benefit from 1 to 2 inches of compost or 5-10-5 fertilizer in spring, and then a repeat application around August in summer.

Pro Tip: Balanced fertilizers contain equal amounts of nitrogen (N), phosphorus (P), and potassium (K). Nitrogen helps your flowers maintain healthy green leaves by producing chlorophyll (the green pigment in plants). Phosphorus aids in nutrient transport in your plants, providing enough energy for flowering. Potassium regulates flower metabolism or how food (sugar) is converted into growth energy.

Calculate the Garden Bed Size

Once you know what type of flowers you have and what fertilizers suit them best, it's time to calculate how much fertilizer your garden bed needs. Grab your measuring tape and measure how long and wide your garden bed is. Then, multiply the length by the width to determine how many square feet you have. If your garden bed is curvy or wavy, you may need to estimate measurements for certain areas. Finally, use the area and the recommendations on the fertilizer label to know the correct amount.

Amend the Soil with Organic Matter

Organic matter is an excellent way to increase soil nutrients. There are different types of organic matter to choose from. Organic compost, aged or decomposed manure, and leaf mold are popular sources of organic matter. Next, go back to your flower variety research to determine how much organic matter you need.

Note: For perennials, you typically top-dress the garden with 1 to 2 inches of organic compost in spring (spread around existing perennials in the garden). If you're planting a new annual garden, add a 1-inch layer of organic matter and work it into the soil to a depth of 4 inches.

Apply Synthetic Fertilizer

If your research indicates that your specific flowers benefit from synthetic fertilizers like a balanced 10-10-10 fertilizer, follow the package guide for application based on your square footage. Synthetic fertilizers typically come in three forms: granular, granular slow-release or controlled-release, and liquid. Each form provides nutrients to your garden over different time frames and has different application methods. Always follow specific recommendations.


Type of Synthetic Fertilizer Duration How to Apply It


Type of Synthetic Fertilizer

How Long It Lasts

How You Apply It

Granular (controlled)

Six to eight weeks

Before planting, use a garden rake to incorporate the fertilizer granules into the soil to a depth of 4 to 6 inches.


Granular (slow-release or controlled)

Three to four months

Use the same method as for granular (controlled). For existing flowers, side-dress and apply it to the soil 4 to 6 inches away from the plant to avoid fertilizer burn. Gently mix the fertilizer into the soil using a rake.



One to two weeks

Dilute the fertilizer with water according to the package guide and water the soil



Fertilizer burn can occur when you apply too much fertilizer to plants or add it too close to the plants. When fertilizer burn happens, the fertilizer adds extra salts to the soil and draws water away from the plant, causing the roots to dry out. You may see yellow, crispy leaves, and your plants may die. Help prevent this issue by applying the fertilizer directly to the soil 4 to 6 inches away from existing plants.

Consider Organic Alternatives

Organic matter and synthetic fertilizers aren't the only ways to fertilize flowers! Depending on the variety, you can also use organic additions like coffee grounds to increase soil nutrients, which can change the soil's acidity or pH to better suit your plants. Eggshells can add calcium to the soil, helping your plants with robust cell walls and cellular-level support. Then, Epsom salt can aid flowers like hydrangeas by injecting magnesium into the soil, which helps prevent leaf yellowing.

Encourage Beautiful Flowers

Learning how to fertilize your garden bed is an excellent way to increase soil nutrients, encourage healthy leaves, and vibrant flowers. Always start by researching your flower varieties, as the best method of fertilizing flowers may vary. Then, measure your garden bed to find out the appropriate amount to apply based on square footage. Next, consider using organic matter, synthetic fertilizers, or even organic alternatives like coffee grounds. Finally, repeat the application according to your variety's recommendations.