One of the biggest concerns with fertilizing are the control products used. Very strict laws control what products can be sold in the state of Ct.
Each chemical first has to go through years of testing before it can be sold. Many products that are sold can only be sold to licensed companies with certified applicators.
If you use the correct materials as directed and keep your lawn as healthy as possible, the chemicals used are less potent and far less expensive than having to replace a badly damaged lawn.
I use all slow release, granular products which under normal conditions last about 8 weeks. This together with liquid weed control are by far the best way to handle your lawns needs.
This can be done once or twice a year. This helps control your soil ph. Soil is best when kept between 5.5 and 7.5. This can be checked by doing a soil sample. In short, keeping the correct soil ph lets your grass use the fertilizer most efficiently.
I use pelletized lime which is gray in color and goes into the soil quickly.