[header] How to fertilize flowers [title] Determine when to fertilize. [step] The type of flower you wish to fertilize, whether it is an annual or perennial, and whether it is new growth or an established plant will all play a role in determining when you need to fertilize. Determine the best time to fertilize your specific flowering plants. 
[substeps] Fertilize the soil for annuals, as well as any new planting, during bed preparation. Fertilize established perennials and ornamental grasses as soon as their growth resumes in the spring.