Best Fertilizers for a Flower Garden

A healthy flower garden is full of plants that are strong and have bountiful blooms. You can achieve these results with most fertilizer types, such as granular, powder, liquid or organic. Which type is best depends on the soil fertility, and you can find out that information by performing a soil test or studying the health of your flowers.

Most fertilizers contain nitrogen, phosphorus and potassium, and flowers need all three nutrients to grow well.

Nitrogen (N) promotes green, leafy growth and seed and fruit development.

Phosphorus (P) is needed for root development and blooms.

Potassium (K) encourages growth and seed and fruit development.

Fertilizer labels display the proportion of each nutrient in three numbers, sometimes called the N-P-K ratio, such as 10-10-10. The first number shows the percentage of nitrogen, and the second and third number show the percentage of phosphorus and potassium. The best fertilizer for a flower garden supplies the nutrients the soil is lacking. For example, a soil that's low in nitrogen but high in phosphorus and potassium benefits from a 21-0-0 fertilizer.

Fertilizers for growing flowers are often high in phosphorus, but overfertilizing can lead to problems if you use high-phosphorus or high-nitrogen fertilizers. Plants need phosphorus to produce plentiful blooms, but many home garden soils already contain sufficient levels. Excess phosphorus from fertilizers washes away during heavy rain, and becomes a pollutant in streams, rivers, lakes, the ocean and other open water sources. Excess nitrogen leads to plentiful green, leafy growth but few flowers.

Before fertilizing a flower garden, find out the nutrient levels in the soil by using a soil test. Some university or county soil test laboratories will analyze your garden's soil at no charge or for a small fee. Home test kits can give you approximate numbers but the degree of accuracy varies.

You can also study your plants. If they bloom well, they probably don't need a high-phosphorus fertilizer. If they're growing poorly and their leaves are pale or yellow, they may be deficient in nitrogen, not phosphorus.

High-phosphorus fertilizer labels display numbers where the middle figure is high, such as 5-10-5 or 15-30-15.

Granular fertilizers are slow-release, and powder and liquid fertilizers quickly release nutrients to plants. Fertilizer granules are semi-permeable. They break down when in contact with water and slowly release nutrients over six to eight weeks or longer, depending on the weather. Warm, moist conditions increase the release rate. Granular fertilizers are often applied in spring and again two or three months later to feed flowers through the growing season.

Powder and liquid fertilizers provide nutrients to flowers almost as soon as they're applied, but rainfall washes them out of the soil and they must be applied frequently for a long-term effect. Powder and liquid fertilizers give flowers a quick boost.

Don't allow fertilizers to touch the leaves or other plant parts. Fertilizers can cause chemical burns. If a fertilizer accidentally makes contact, rinse the plant with plenty of water.

Compost, aged manure, blood and bone meal and guano are some organic fertilizers for flowers. Organic fertilizers supply the major plant nutrients nitrogen, phosphorus and potassium, and they often contain micronutrients, such as zinc, boron and iron. They can be slow-release, such as compost and aged manure, or fast-release, such as guano. Compost and manure also improve the texture of the soil.

Commercial organic fertilizer labels display the three numbers that show how much nitrogen, phosphorus and potassium they contain, and they can correct soil deficiencies in the same way as chemical fertilizers. Compost and manure can be high in nutrients, and overuse of these over several years can lead to excess nutrients in the soil.

Applying fertilizers to a flower garden involves calculating the correct amount to apply. A soil test report usually advises how much actual nutrient the soil needs in a certain size area, such as 0.25 pound -- 1/4 pound -- nitrogen per 100 square feet.

To calculate the amount of fertilizer to use, first convert the figure in the fertilizer ingredients to a decimal figure. For example, the 10 percent nitrogen in a 10-10-10 fertilizer would become 0.10. Then multiply the amount of nutrient needed by the decimal figure. For example, 0.25 nitrogen multiplied by 0.10 equals 2.5 pounds of fertilizer.

To calculate the size of a flower garden in square feet, multiply the length and the width of the garden in feet or use an online calculator. For example, a garden measuring 20 feet long and 5 feet wide has an area of 100 square feet.

For more information on setting the stage for healthy flowers, see How to Prepare the Soil for a New Flower Bed