Become a Smarter Gardener in 2019: Fertilizing Annual Flowers

Photo: Julie Weisenhorn, UMN Extension

Annual flowers give us summer long blooms, but these plants have a shallow, temporary root systems that require additional water and regular fertilizer. If you have been disappointed with flowers on annuals, it may be due to a lack of fertilizer, or possibly a lack of water or sunlight.

What kind of fertilizer?

Begonias, impatiens, petunias (especially wave petunias) and even geraniums, an easy to grow, carefree annual, grow larger and with more flowers when they have regular fertilizer. I use a slow release fertilizer in the planting hole when I plant annual flowers and then use a liquid fertilizer once a week throughout the summer.

Photo: Julie Weisenhorn, UMN Extension

Plants in the ground can get by with less water and fertilizer, but plants in containers will require your constant attention all summer, daily watering and weekly fertilizer is a standard to consider using. I use a complete fertilizer for the slow release and liquid feeding. An analysis of 20-20-20 is a common ratio for liquid fertilizer, with nitrogen, phosphorus and potassium respectively being the three
elements in this analysis.

Read more about fertilizing container plants, here!

Using a fertilizer injector at the end of your hose is an easy way to apply the liquid fertilizer. My annuals are in containers with soil that I have been reusing for a few years, so the nutrient level is low. A flower bed in the ground in garden soil may be much higher in nutrients and the only way to know is to have a soil test, and apply fertilizer according to the recommendations from the soil testing lab.

Help annuals look great with a little more attention...

Some people fertilize “weekly weakly” or with a dilute fertilizer on a weekly basis. This can be a good practice for indoor houseplants or slow growing plants that are growing on a year round basis.

Our summer annuals, especially container plants, may need more than the “weekly weakly” fertilizer. Weekly liquid fertilizer at normal rates is a good rule of thumb for actively growing annual flowers.

The water leaching out of my flower containers falls to the ground into another flower bed. Smart conscientious gardeners start with a soil test to know what nutrient levels are in their soil. Using nutrients only on plants that need them is a responsibly and conscientious way to garden.

Author: Mary H. Meyer, Extension Horticulturist and Professor