Next you review which type of fertilizer is best suited under the specific circumstances. Then you make your choice.
When it comes to lawns, I personally would use an organic product in spring on both cool and warm season lawns. This gives a gradual feeding early, just enough to keep cool season lawns green and growing through summer but without inducing a flush growth which can deplete storage reserves.
Warm season grass should not be fertilized too early in spring, and the slow release rate of organic fertilizers in cool soil matches the warm season root growth very nicely.
During hot summer months, using organic fertilizers provides some security for warm season gardeners as salt based fertilizers can burn lawns during the hottest months. Slow release coated fertilizers are preferred if synthetic sources are pursued. A cool season lawn should not be fertilized in summer with either synthetic or organic fertilizers.
In early fall, soil temperatures are typically warm enough to support either organic or synthetic fertilizers.
In late fall, warm season grass should not be fertilized. Cool season lawns benefit tremendously from a single application with a quick release fertilizer after the top growth stops, but while the grass is still green (November). Using an organic, or a slow release coated synthetic, fertilizer at this time will just leave the product suspended until next spring which defeats the purpose of the application. A soluble quick release synthetic fertilizer like ammonium nitrate or urea is here the best choice by far.
