Many varieties of lettuce are sold in supermarkets. Even more are available for planting in garden centers and seed catalogs. Leaves may share certain characteristics, but ultimately each type of lettuce is best identified by flavor. Some lettuces, such as black-seeded simpson and valerie, are sweet and light, almost melting on the tongue; others, such as arugula and dandelion, are crisp and have bite.
Head lettuces are named because they grow in a head formation. Some, such as iceberg, feature tight leaves that wrap around each other down to the core; these are called crisphead lettuces. Others, such as butterhead and bibb lettuce, have looser heads. These looser heads look something like a rosette. Head lettuces tend to be various shades of green.
Leaf lettuces are all the lettuce types that do not grow in a head formation. This variety encompasses romaine, endive, escarole, red-leaf, green-leaf and oak-leaf lettuces found in supermarket produce sections. Many other leaf lettuces, including black-seeded simpson and valerie, are available to the home gardener. Romaine has long, slightly crisp leaves that are dark green at their rounded tips and fade to lighter green and white toward the base. Endive and escarole have thin, long green leaves with frilly, serrated edges. Red- and green-leaf lettuces are slightly frilly and are so named because they are red and green. Oak-leaf lettuce features light green leaves shaped like the leaves of an oak tree.
Mache, dandelion, chicory, arugula and mesclun are salad greens commonly packaged with lettuces in stores. Mache has tiny round leaves, and may also be referred to as a “microgreen” in the culinary world. Dandelion and chicory are relatives, and have leaves that are very similar in shape: dark green, long and serrated. Arugula looks similar to these two, but is slightly shorter and wider. Mesclun may have deep green or red serrated leaves.
Lettuces are easy to start from seed. All lettuces, no matter the type, grow best in cool weather. Lettuce seeds require light to germinate, so they must be sown with a minimal amount of soil covering them. Leaf lettuces can be harvested a few leaves at a time with no ill effect. Leaves will grow back after they are harvested, as long as a gardener does not harvest all the leaves from a single plant at once. Head lettuces should be harvested whole. All lettuces begin to bolt (send up seed stalks and set seed) when the weather is consistently hot (85 degrees Fahrenheit or above). Leaves become tough and bitter when seed stalks have emerged.
Leaf lettuces are generally more fragile than head lettuces. While a wide variety exist, many of them wilt so quickly once they are picked that it is not feasible to sell them in stores. Gardeners hoping to experience the delicate delights of these types must grow them for themselves.