|Lettuce (Lactuca sativa)|
Most people group lettuce into two broad categories, leaf and head, but according to the University of Illinois Extension there are five distinct types of lettuce. (Find a complete description of leaf, romaine, crisphead, butterhead and stem lettuces and recommended varieties for each on the Extension page.) No matter what type of lettuce you plant, it is important to know that all varieties prefer cool air and soil temperatures, with a few varieties willing to tolerate warm temps. Because of this preference, lettuce is a perfect choice for a northern gardener to include in their backyard garden! :D When mid to late summer approaches & temperatures start to head up to 80F+, most lettuce will bolt (shoot up a flower stalk), and become bitter to the taste. Consider extending the life of your spring crop by mulching the soil when temperatures start to rise. You may also want to plan your garden so that the lettuce is shaded by a larger plant or one of your vertical structures, for a vining crop like pole beans or cucumbers, when the mid-summer heat arrives.
Lettuce seed is small and should be individually seeded or broadly scattered and quickly thinned to at least 3 inches apart for leaf lettuce, 6 for a loose head and 12 for a firm head variety. Some seed companies sell seed packets which include filler to help you scatter the seed thinner, but most often the gardener will still need to thin to get optimal growth and harvest. (My best experience was to plant according to a square foot gardening plan which was 9-12 individual seeds in a one foot square patch.) Seeds should be placed about 1/4 in deep.
Lettuce can be started indoors 4-6 weeks prior to the average last frost for a spring garden or mid summer (for us northerners) for a fall crop. Starting seedlings indoors works especially well for fall gardens since high temperatures can hang on late into the summer some years. Plant seedlings outdoors when temperatures constantly stay in the 70's or cooler in the fall.
Harvest as soon as the leaves are big enough to eat. Cut off the whole plant or pull off individual leaves for a continual harvest. Leaves will be most crisp in the morning, but can be harvested throughout the day if you desire a fresh salad for a late day meal. Rinse leaves in cool water and dry with a towel or salad spinner before serving or storing. Storage life for fresh lettuce is about one week in a refrigerator.
Happy Gardening! :)