Perennial ryegrass (Lolium perenne) is a smart choice for a lawn grass in many areas of the country because it is attractive, easy to establish and can stand up to foot traffic. The short-lived perennial may not be the best grass for northern regions, though, because it suffers some degree of winter injury in U.S. Department of Agriculture plant hardiness zone 5 and below. With proper seeding techniques, perennial ryegrass germinates quickly and makes vigorous early growth.
You can successfully plant perennial ryegrass whenever temperatures are mild and moisture is abundant. This cool-season grass can't thrive in hot, dry conditions, so the seeding date should allow ample time for the grass to become established before it is stressed by heat or drought. Ryegrass can germinate and grow during chilly weather, but where weed pressure is high, it is best to till the soil first then plant the seed when soil temperatures have risen to perhaps 55 degrees Fahrenheit. This helps the ryegrass compete against weeds.
Late summer or early fall is often the best time to plant ryegrass seed. Weeds are much less of a problem at this time of year, and you have plenty of time during the preceding summer months for cultivation and seedbed preparation. Also, air temperatures are decreasing to a range that supports vigorous ryegrass growth, but the soil is still warm enough for rapid germination. As a general guideline, you should plant ryegrass seed about 30 days before the first frost, when temperatures are mild but enough warm days remain to allow for adequate growth before winter.
You may think that spring is the best time to sow seeds of all kinds, but this is not always the case. A wet spring delays seedbed preparation, and excessive rainfall can leave you with cold, wet soil that causes seeds to rot instead of germinate. Also, a cool spring followed by hot, dry weather in early summer is tough on perennial ryegrass, which ceases to grow at temperatures above 85 degrees F. Nevertheless, spring may be a more reliable seeding time in areas where the fall is subject to low rainfall or early bouts of severely cold weather. You usually want to try your first spring sowing as soon as the soil is prepared and warm enough to allow for decent germination -- usually between 50 and 60 degrees F.
Perennial ryegrass is a good candidate for frost seeding. With this technique, you can get a good stand of grass without much labor, and the labor comes at a time when you are not busy with other garden and lawn chores. Frost seeding simply means broadcasting the seeds onto an unprepared soil surface in late winter or very early spring. You should spread the seed after snow has melted but when the soil is still freezing during the night and thawing during the day. This freeze/thaw cycle helps to work the tiny grass seeds into the soil and protect them until the soil warms up enough for good germination.