“The annuals in my containers seem to have stopped growing, and the foliage of the plants has a bit of an off-green color and is even looking a bit yellow. The containers are in full sun with sun-loving annuals. What can I do to help my plants and get my color back for the rest of the summer?”
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— Wendy Leyton, Lombard
I will assume you used a high-quality growing medium for your containers and did not use garden soil. A lightweight commercial soilless growing medium needs to be used in containers to ensure proper drainage and aeration for the annuals to grow properly.
Your containers also need to have drainage holes in the bottom, or water can back up in the pots and cause your plants to stop growing with off-color foliage. Eventually the plants will die from too much water in this situation.
It is likely your containers need to be fertilized. The more frequent watering of containers with established annuals during the hot summer days will leach nutrients out of the medium, resulting in “hungry” plants that will have reduced growth and off-color foliage like you are describing.
Use a liquid fertilizer to give your containers a boost. Fertilizing once every three to four weeks should be adequate to bring your plants around. Over-fertilizing can result in large, green plants with reduced flowering.
Fertilize when the growing medium is moist to avoid burning your plants. Try adding a granular slow-release fertilizer when you plant your containers next year. These fertilizers slowly release nutrients over a period of time and can be beneficial for container gardening.
On occasion, I will see a bed of annuals in a garden that is stunted and not flowering well. Overwatering and wet soils, as well as sun annuals planted in too much shade, can cause this too, but if these scenarios can be ruled out, then a liquid feed for annuals growing in a bed can be beneficial, too.
For more plant advice, contact the Plant Information Service at the Chicago Botanic Garden at [email protected]. Tim Johnson is senior director of horticulture at the Chicago Botanic Garden.