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The best time to plant grass seed depends on your local climate and whether you have cool-season or warm-season grass.

For cool-season grasses (like tall fescue), the ideal time to seed is late summer or early fall (typically August and September). During this period, the soil is still warm from the summer, but the air is cooler, creating optimal conditions for germination and root establishment before winter. There is also less competition from weeds. Spring is a secondary option, but cooler soil temperatures, the risk of a late frost, and less time for the grass to mature before summer heat can make it less successful.

For warm-season grasses (like St. Augustine), the best time to plant is from late spring through mid-summer (typically May and June), when temperatures are consistently between 75 and 90 degrees Fahrenheit.

In general, it is best to avoid seeding during winter or early spring, as cold soil and air can prevent seeds from germinating. For recommendations tailored to your specific grass type and climate, consider consulting a local lawn care professional.

First, you should figure out whether you have dormant or dead grass. Dead grass won’t come back, so you’ll have to reseed if you’re hoping for a lush lawn. However, grass can go dormant if it hasn’t received enough water or if temperatures are too cold. If it’s still decently warm outside, you can revive dormant grass by watering it. But if it’s mid-January in New England, for example, you’ll need to wait until the weather warms up again. If you want to keep grass green in winter, consider a grass like Kentucky bluegrass, which maintains its color year-round.

Adding seed to existing grass is often known as overseeding, as opposed to reseeding. Reseeding refers to the process of filling in bare or dying patches of lawn—or in some cases, full lawns—whereas reseeding supports existing lawns to prevent thinning. Overseeding is an ideal annual lawn care practice for grass fighting drought, disease, weeds, or pest issues.

Provided you're using an appropriate starter fertilizer for grass seed, you can put down seeds and fertilizer at the same time. However, putting them down separately, one after the other, on the same day will help to avoid over- or under-applying the lawn food. Avoid using a fertilizer with weed control elements, as these will likely keep the grass seeds from starting.