Spring is the best time to fertilize flowering plants and I use a slow release plant food like Osmocote every spring around perennial plants. Then I use Osmocote around annual plants when they are added later in the spring but also use a fast acting liquid plant food on annual plants in mid summer if they look like they are pale green or lack blooms. It does depend on what type of flowers you are growing as some flowers such as roses are very hungry plants while others like lavender require very little fertilizer to no fertilizer. Keep growing, Marianne Binetti