Lawn care calendar for Connecticut: when to fertilize and seed

Dates and the 3 inch mowing height come from UConn fact sheets and posts; phosphorus is limited by law on established lawns, with an exception for seeding, sodding and overseeding.

Which grasses grow where in Connecticut

UConn says only four cool-season species make an acceptable dense lawn in New England: Kentucky bluegrass, perennial ryegrass, fine fescue and turf-type tall fescue. Kentucky bluegrass is the most widely used. Both bluegrass and ryegrass want fertile, well-drained soil with a pH of 6.0 to 7.0, extra water in hot dry weather and more fertilizer than fescue.

Fine-leaved fescues take the least fertilizer and need as little as four hours of direct sun a day. The guidance for them is a height of 3 inches and a maximum of 2 pounds of nitrogen per 1,000 square feet a year, or 1 pound if clippings are returned. Along roads and sidewalks, fine fescue and turf-type tall fescue tolerate de-icing salt better than bluegrass and ryegrass.

Frost dates from NOAA

Dates are the NOAA 1991-2020 normals for the last spring and first fall 32 F freeze at 50% probability. At Hartford (Bradley International Airport) the last spring frost averages April 21 and the first fall frost October 16. At Bridgeport (Sikorsky Memorial Airport) the dates are April 5 and November 6.

Counting the days between them, the shoreline at Bridgeport averages about 215 frost-free days against 178 inland at Hartford (our arithmetic), a gap of more than five weeks. UConn reminds you that grass wakes when the soil passes 50 F, which is a better trigger than the calendar for spring jobs.

Spring

Sunny areas green first, shade later, and Kentucky bluegrass is slower to green than perennial ryegrass. Spring is a time for checking road-salt damage and sharpening mower blades, since dull blades shred leaf tips, which helps disease develop, and a clean cut heals fastest. Spring seeding gives mixed results: grasses need time to root before hot weather, and young grass may need a deep watering once a week in a dry spell.

Crabgrass is the other spring job. UConn says to keep the lawn at 3 inches, because a taller lawn shades crabgrass seed and keeps it from germinating, and treats herbicides as a tool for places where crabgrass is a chronic problem. Two preventer products let desirable seed grow, so they can go down at seeding. Post-emergent herbicides work best on crabgrass with two to four leaves.

Summer

Cool-season lawns should not be fertilized in summer, especially with fast-release nitrogen, because the grass slows or goes dormant in heat while crabgrass, an annual on a short clock, takes advantage. UConn's photo of a 3 inch lawn beside a lower-cut strip shows crabgrass only in the lower one. Grub control in spring is hard, because the grubs are larger and about to pupate.

Seeding has a hard stop: UConn says the latest date has always been before October 4, since soil below 50 F slows germination and frosts chill the soil well into the morning.

Fall

August 15 through mid-September is the best time to establish or renovate. Aerate first if the lawn is badly compacted, then slice-seed; sod needs about three weeks before the first mowing. Fall is also the time for lime: typically 50 pounds per 1,000 square feet, repeated at 30 day intervals if the pH has a long way to rise, then 50 pounds every other year once it reaches the mid-6s.

September through mid-October is the fertilizing window, with 1 pound of nitrogen per 1,000 square feet, and UConn says to get it down by October 15, because growth slows after that and weather becomes unpredictable. Put the spreader on a calibrated setting and water lightly if no rain is coming, so granules do not stick to the grass.

The phosphorus law

A Connecticut law passed in 2013 limits phosphorus on established lawns, because phosphorus is the number one inland freshwater pollutant in the state and feeds algae and toxic cyanobacteria. Maintenance fertilizers sold in the state usually have analyses such as 30-0-4, 29-0-5 or 10-0-6. UConn says fertilizer containing phosphorus can still be used when seeding, sodding or overseeding. I did not open the statute itself, so check the current section before relying on details such as soil test exceptions.

The lawn fertilizer calculator on this site converts the nitrogen percentage of a bag into pounds of product for your lawn size, which makes the 1 pound target easy to hit with a zero-phosphorus lawn food.