My knockouts have not bloomed for 2 years. I had my soil tested and it is over optimum in all categories, NPK. pH is 7.1. Should I add nothing? A local nursery recommended Dr. Earth Flower Girl Bloom Booster, which is 1-9-2. Good idea or no because I already have high Phosphate?
Knockout Roses Not Blooming
I would stick with feeding your roses a well balanced fertilizer. The Dr. Earth would be okay since it is relatively low on the nitrogen end. Rosebushes not bloom can be caused by high nitrogen fertilizers which encourage more foliage growth and few to no blooms. It can also be caused by too much shade and not enough good sunlight. At least 6 hours of good sunlight is needed. It can also be caused by tiny pests that get at the buds in their smallest of form and thus cause them to fall off. It may be time to try a systemic approach and see if that allows the buds to form and blooms to come. I would try treating all the rosebushes with some Bayer Tree & Shrub Granules. Apply per the label instructions for Ornamentals/Roses. It has some food in with it for the roses to help give them strength too. After that treatment, in about two weeks, water all the rosebushes with some water that has a product called Super Thrive in the water. The super thrive provides great vitamins and hormones for the rosebushes overall health that will encourage bloom production.