Lettuce is a hardy crop that can be started throughout the growing season. It prefers cool temperatures, growing best at 16°C to 19&degC. Approximately 900 seeds / gram.
Hints:

Plant 7 mm [1/4"] deep in rows 30 to 60 cm [12-24"] apart.

Thin to 20 cm [8"] rows.

Plant 2 to 3 times deeper in the fall for the earliest spring lettuce.

Grand Rapids - 45 days. Plants large, erect and compact. Leaves bright green, broad with waved and frilled margins. One of the most popular loose-leafed varieties for home gardens and greenhouse forcing. Tipburn resistant and slow bolting.