Lettuce is a short growing season plant, that is why it is more and more popular as a spring vegetable cultivated under the cover. It is mainly grown on substrates such as mineral wool and hydroponic systems. In heated greenhouses, lettuce can be produced all year round. Seedling production lasts from 3 to 6 weeks. Optimal germination temperature is within a range from 18°C to 20°C.
Similarly to other crops, light is one of the most important production factors. Light deficiency might be particularly harmful for seedling and lettuce at the time of the head increase.
Inappropriate lighting, can cause the internodes to lengthen and slow the absorption of nitrogen compounds. Lettuce belongs to the long day. To ensure its optimal growth conditions, it needs at least 12 hours of light access. Especially in autumn and winter periods, it is necessary to use additional lighting sources.