|'White Summer', a white-seeded heirloom variety also known as 'Hubbard's Market', 'All-Year-Round', and 'Top Notch', is a butterhead or cabbaging lettuce with dark green, crinkled leaves whose edges are straight. This is an excellent variety to grow farther North. In the South, it is best grown as a fall lettuce. Start from seed 4 to 6 weeks before average last frost date. Sow seeds 1/4 inch deep in wide rows and thin to 8 to 12 inches apart. Thinned seedlings can be replanted. Keep soil moist but not soggy. Protect from rabbits and slugs. Extend the harvest season by planting successive crops. Summer heat causes lettuce to bolt. Pick outer leaves as they grow or harvest all at once. Harvesting when weather or day temperature is cooler will result in crisper leaves. Do not harvest lettuces until you are ready to use it.