How Does Nitrogen Fertilizer Affect Marigolds?

Nitrogen Function

• Nitrogen causes plants to increase the production of leaves and other green growth. It does not encourage the development of flowers, the chief reason that most gardeners choose to use marigolds in the landscape. In fact, overuse of nitrogen can delay flowering, as the plant pours its energy into producing new leaves and stems for three to four weeks.

Fertilizer Recommendations

• Marigolds are annual plants that last only a single summer, so maintenance of the soil to promote long-term health doesn't become an issue for marigolds as it does for perennial plants. While the Clemson Cooperative Extension recommends amending soil with organic matter when transplanting marigolds into the garden, it does not recommend the use of any fertilizers. The organic matter will provide small doses of nutrients throughout the growing season.

Growing Marigolds

• Starting marigolds from seed requires a little extra care in terms of fertilizer. Because you want to establish dense, green growth so that the plant has a source of energy, you will use nitrogen fertilizers when growing marigolds from seed. Fertilizers high in nitrates encourage abundant leafy growth in preparation for blossoming. Marigold growers typically use fertilizers that contain between 15 and 20 percent nitrates. Avoid fertilizing seedling transplants for a week to 10 days or until the roots reach the sides of the container. As you prepare to transplant the marigolds into your garden, cut fertilizer doses in half. Always follow application rates suggested on the fertilizer packaging and avoid ammonium-containing fertilizers that can cause root damage.

Other Nutrients

• Other nutrients may provide more beneficial effects for your marigolds. Phosphorus encourages the development of flowers and healthy root systems. Potassium helps plants to resist environmental stresses, like drought or a pest problem. When starting marigolds from seed, fertilizers high in potassium help to achieve healthy plants. Use caution when applying fertilizers that contain micronutrients, as some marigolds have a high sensitivity to overapplication of micronutrients.