Lawn (Cool Season)

Cool-season lawns in New Hampshire and Vermont — typically Kentucky bluegrass, perennial ryegrass, fine fescue, and tall fescue — have a growth pattern that is the inverse of warm-season grasses: they grow most actively in spring and fall when temperatures are 60-75°F, and slow dramatically or go dormant during summer heat. This growth cycle dictates a fertilization schedule that many homeowners get exactly backwards. The single most important fertilization window is late summer through early fall (late August to early October), not spring. Fall feeding fuels root development, thickens the turf canopy, and stores carbohydrates in the crown and root system that fuel the earliest spring green-up. Heavy spring fertilization — which many homeowners favor because of the immediate visual payoff — actually produces excessive top growth at the expense of root depth, increases thatch accumulation, and makes the lawn more susceptible to summer heat stress, drought, and fungal diseases like brown patch. Nitrogen is the nutrient that most limits turf growth, and a well-maintained New England lawn needs 2-4 pounds of actual nitrogen per 1,000 square feet annually, divided across 3-4 applications. Potassium is the second most important nutrient, building cold tolerance and disease resistance. Phosphorus requirements are usually met by existing soil reserves, and many northeastern states now restrict phosphorus in lawn fertilizer to reduce waterway runoff unless a soil test documents a deficiency. Slow-release nitrogen sources are strongly preferred over quick-release formulas, providing steady feeding over 6-8 weeks without the surge-and-crash growth pattern that stresses turf.