No matter the quality of the soil in your hanging basket, it is simply unable to contain enough energy to sustain quality plant life for an entire season, especially with multiple plants crowded into a small pot. In fact, without added nutrients, most flowering baskets begin to fail by mid-summer, if not earlier.
FERTILIZING: The key to fertilizing hanging baskets is a slow, steady approach. All potted annual plants need to be fertilized in order to keep their strength and vitality. Eventually, the soil in your basket runs out of available nutrients for the plants. Fertilize one time per week.
COMPOST TEA: Compost tea is a great all-purpose liquid fertilizer. To make, simply mix a few shovelfuls of fresh or bagged compost in a 5 gallon bucket with water and allow it to steep for about 7 days. Be sure to stir the mixture daily to help the water absorb the nutrients from the compost. Strain the Compost Tea into another container for watering. Put the leftover compost into your flower beds.
WORM CASTING TEA: Just like Compost Tea, Worm Casting Tea is a perfectly balanced, nutrient-filled fertilizer. You can purchase bags of worm castings at most garden centers. Just mix 1/2 cup of castings with 1 gallon of water. Let it steep for 24 hours, and then water plants.
FISH EMULSION: Fish emulsion is another great choice for potted plants. It can be purchased in liquid form. Just dilute for a quick and easy liquid fertilizer.
WATER: It cannot be stressed enough that your baskets get watered regularly at the same time each day and are not allowed to dry out. As temperatures soar, you may need to water twice per day, especially for smaller baskets.
DEADHEADING & TRIMMING: It is also important to deadhead spent blooms on a regular basis to promote new blooms and to trim your plants when they become scraggly around mid-Summer.