Lettuce - Webbs Wonderful This is a crisp, tender, medium sized iceberg type with large firm hearts and succulent leaves. It is slow to run to seed. Sow outdoors thinly from March to July where they are to crop, 1.5cm deep, directly into finely-prepared, fertile, moisture-retentive soil, which has already been watered. Allow 30cm between rows. Early sowings may benefit from cloche protection. Seedlings usually appear in 7-14 days. Thin out to 20cm apart. Water well until plants are established. Regular sowings, made every two to three weeks, will ensure a continuous supply. Harvest from May to October.