Fertilizers may be granular, formulated for slow release, or soluble in water. Granular fertilizers are common for field applications. Slow release is most often used as a top dressing for container or field grown plants. One application can last many months.
Soluble fertilizers are usually made as stock solutions and applied using an injector that dilutes the fertilizer to the proper concentration. Fertilizers are usually applied soon after cuttings root or seedling emerge.