Lettuce is undoubtedly one of the most popular fresh vegetables and can be found in the garden, including greenhouses and cold frames, be harvested from late April to November.
Lettuce owes its refreshing and stimulating effect to its lemon content- and malic acid and a bitter substance, which is mainly located in the veins of the leaves. The veins of the leaves must therefore be eaten as well. The head formation is based on a growth inhibition of the young shoot, which initially develops numerous leaves without any visible growth in length, the, overlapping and pressed tightly together, form the more or less solid head. By certain external influences, z.B. the day length, this growth inhibition is lifted, the sprout pierces the leaf canopy and "shoots" into bloom. According to this growth behavior, lettuce is divided into two groups. First, the so-called long-day forms, where firing is triggered by the long tag. This includes all varieties for cultivation under glass and plastic as well as the earliest outdoor and winter varieties.
Second, the tag-neutral forms, whose shooting is not affected by the length of the day. This includes all early summer- and summer varieties.