By our calculations, you should look at sowing Organic Heirloom Lettuce Seed Mix about 53 days before your last frost date.
Start in flats or direct seed. Cold frames extend season. Fertile, composted soil that is loose, not too acid, well-drained, and in good tilth with adequate nitrogen and moisture promotes fast growth for best flavor. In hot climates use shade cloth mid day to keep plants cool. Plant every three weeks for continuous harvest.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Organic Heirloom Lettuce Seed Mix is a half hardy plant.