Annual ryegrass (Lolium multiflorum Lam.) is a common cool-season forage in the southeastern US that is often overseeded into established perennial pastures. Yield is typically greater in early spring than winter, and management to achieve greater growth during late autumn/winter could increase total seasonal production. A field experiment was conducted to determine ryegrass dry matter yield as affected by seeding date and irrigation during early seedling development. Ninety-six plots were established at 2-week seeding-date (S-n) intervals (16 plots/date) at the E.V. Smith Research Center Plant Breeding Unit in Tallassee, AL, beginning in September and ending in November 2008, 2009 and 2010. Cultivars were Marshall, Gulf, Shiwasuaoba, and the experimental SWIPAR. The experimental design was a randomized complete block (n = 4) with split-plot restriction on randomization in which irrigation treatments (+, –) were assigned to main plots and cultivars were assigned to subplots. Immediately after seeding, 2.54 cm of water were applied via a drip system to irrigated plots. Water was applied for 2 weeks thereafter based on evapotranspiration (ET), and was gradually reduced to 65% ET. Plots were harvested when forage canopy height reached 20 cm. A total seasonal yield loss of 786, 2,149 and 5,145 kg/ha in 2008, 2009 and 2010, respectively, was observed for plots seeded each day prior to S-3. An inferred yield loss of 2,335, 2,605 and 7,652 kg/ha in 2008, 2009 and 2010, respectively, was observed for each day’s delay in seeding past S-3. Data are interpreted to mean that maximum seasonal yield can be achieved with earlier seeding of annual ryegrass, and that later seedings cannot attain the yield potential of earlier dates.