Should I be adding fertilizer?
Each lawn is different - different grass varieties, different soils, different pH, different nutrients, maybe even some weeds and pests. All of these characteristics need to be considered before applying any product to your lawn, whether it's lime, fertilizer, or something to address a pest. The best way to learn about your lawn and what it needs is to do a soil test. A soil test from the University of Maine will not only tell you the current soil conditions of your lawn, but will also tell you how to correct any conditions that are poor in your soil.
You don't want to assume that your lawn needs fertilizer as it could be a waste of your time and money while also harming our local water bodies like Capisic Brook, the Fore River, and Casco Bay. If you are leaving your grass clippings while mowing, have clover in your yard, use compost tea, or topdress with compost, your soil might already have all of the nutrients it needs but another soil condition, like pH, is making it harder for your lawn to grow.