Does Nitrogen Affect Flowers?

Nitrogen and Flowering Plants

• A nitrogen deficiency affects the entire flowering plant. The plant is often spindly with pale yellow-green leaves. Flowers cut from nitrogen-deficient plants may have a short shelf life. Too much nitrogen in the soil may lead to large, leafy green plants with reduced flower production.

Soil Testing

• To accurately determine the soil nitrogen content, perform a soil test. This may be done by a commercial lab or by a do-it-yourself soil test kit. Because phosphorus and potassium are also important soil nutrients, a soil test often tests for all three -- including nitrogen. Use the results of the soil test to select the appropriate fertilizer for the flowering plants.

Fertilizer Grades

• Each type of fertilizer used for flowers is given a fertilizer grade. A fertilizer grade is a series of three numbers representing the amount of nitrogen, phosphorus and potassium in the fertilizer. The first number indicates the amount or percentage of nitrogen. For example, a grade of 15-0-0 shows that the fertilizer contains 15 percent nitrogen.

Nitrogen Fertilizers

• Both organic and inorganic fertilizers provide nitrogen to flowering plants. Urea has a fertilizer grade of about 46-0-0 (according to the Iowa State University Regional Extension website), while ammonium sulfate has a grade of 21-0-0. The grade for blood meal is 12-1.5-.6 and nitrate of soda is 16-0-0. Fertilizers that contain nitrogen, phosphorus and potassium may have grades such as 10-10-10 or 5-10-5.

Types of Fertilizers

• Fertilizers for flowers are available in several forms. They may be quick-release, water-soluble or slow-release. Apply quick-release fertilizers at planting and every 4 to 8 weeks during the growing season (according to the North Carolina State University Cooperative Extension website). Apply water-soluble fertilizers every 2 weeks. Slow-release fertilizers only require two applications during the summer, one at planting and the second midway through the summer.

Fertilizer Application

• Work the fertilizer into the top 4 to 6 inches of soil when planting flower seeds or plants. Broadcast or sprinkle the fertilizer in the flower garden with established plants. Keep the fertilizer granules from touching flower bulbs, flower stems and perennial crowns.