Lettuce is generally ready to harvest depending on the type and growing conditions, typically between 30 to 70 days after planting. The best time of day to pick lettuce is in the afternoon or evening when nitrate content in the leaves is lower. Here are key harvest times by variety:

• Lamb’s lettuce can be harvested as early as late February and can continue through winter.
• Loose leaf or cut-and-come-again lettuce can be harvested from late April or early May.
• Butterhead, oak leaf, and romaine lettuces are ready between May and September.
• Iceberg lettuce is typically harvested from July to September.
• Batavia lettuce can be harvested from June to October.

For romaine lettuce, the leaves are ready about 65-70 days after planting seeds, but outer leaves can be harvested earlier (around 21 days) using a cut- and-come-again method. The lettuce leaves should have a vibrant green color and the head should feel firm for firm varieties. Bolting (flowering) is a sign to harvest immediately as leaves become bitter. Avoid harvesting when leaves are wet or in the rain to prevent spoilage. In summary, lettuce readiness varies by type and how it is grown, with most ready within 1 to 3 months, and there are methods to harvest leaves progressively before full maturity for ongoing yield.