K-State Research and Extension

Q: I was told to add nitrogen to my annual flowers to make them bloom better. Is this true?
A: Modern annual flowers have been bred to flower early and over a long period of time. They are not as easily thrown off flowering by high nitrogen levels as vegetables are. As a matter of fact, providing nitrogen through the growing season (sidedressing) can help maintain an effective flower display for warm-season flowers. Apply a high nitrogen sidedressing four to six weeks after flowers have been set out. Additional fertilizations every three to four weeks can be helpful during a rainy summer, or if flower beds are irrigated. Common sources of nitrogen-only fertilizers include nitrate of soda, urea, and ammonium sulfate. Blood meal is an organic fertilizer that contains primarily, but not exclusively, nitrogen. Use only one of the listed fertilizers and apply at the rate given below. Nitrate of soda (16-0-0): Apply 1/3 pound (.75 cup) fertilizer per 100 square feet. Blood Meal (12-1.5-.6): Apply 7 ounces (7/8 cup) fertilizer per 100 square feet. Urea (46-0-0): Apply 2 ounces (1/4 cup) fertilizer per 100 square feet. Ammonium Sulfate (21-0-0): Apply 4 ounces (½ cup) fertilizer per 100 square feet. If you cannot find the above materials, you can use a lawn fertilizer that is about 30 percent nitrogen (nitrogen is the first number in the set of three) and apply it at the rate of 3 ounces (3/8 cup) per 100 square feet. Do not use a fertilizer that contains a weed killer or weed preventer.