Tom Thumb Organic Lettuce Seeds 4098 Heirloom Vegetable. Here is a miniature butterhead type lettuce about the size of a tennis ball that is ideal for individual salads. Dark green fleshy leaves wrap around a creamy yellow mild flavoured interior. Tom Thumb tolerates high temperatures and resists bolting. This often overlooked lettuce has been grown for over 150 years â€“ that should tell you how good it is!