The two most common problems when geraniums are not blooming well are too little light or too much fertilizer. Geraniums are sun loving plants and need four to six hours of sunlight a day. Without enough sunlight, the plants will tend to grow taller in order to reach for additional light. The number and size of flowers is often directly related to the amount of sun the plant gets.
When geraniums get to much fertilizer, the plants tend to be large, green and lush with fewer blooms. When geraniums are planted in containers, fertilizer should only be applied approximately once every three to five weeks. Any water soluble fertilizer should be sufficient.
Geraniums planted in an outdoor garden area need to be fertilized even less frequently, approximately once every four to six weeks. It is better to under fertilize than over fertilize geraniums.