Written by Spirekassen 15 Sep 2022 08:25

Cultivating lettuce in the greenhouse



We have entered the first month of Autumn. The days are getting shorter and the nights longer. Soon you will be removing your tomato plants, cucumber plants and chilli plants. They are probably looking tired after a long summer. However, you can continue to use the greenhouse for cultivation by having lettuce the next couple of months. Lettuce can survive the cold and still be thriving.

The secret of lettuce

Lettuce (Lactuca sativa) has a secret you should know. This lettuce plant counts the number of daylight hours in a day. This means that the plant can feel whether we are headed for summer or winter. This is important to know when you are deciding which seeds you want to sow for your winter lettuce cultivation in the greenhouse.

Lettuce can be divided into three main groups

Long-day plants, short-day plants and day-neutral plants. If you sow one of the varieties that does not belong to the current season, it will quickly start to bolt, get a bitter taste and set seeds. Lettuce that is bolting does not taste good at all.

You should choose short-day varieties or day-neutral varieties for lettuce cultivation during winter

If you choose the right variety for the season, you can cultivate lettuce most of the year. During autumn and winter, lettuce can easily be cultivated in a greenhouse.




Good to know about lettuce

Seeds from lettuce germinate ideally in temperatures below 20 degrees Celsius. In September, the temperature may still be too high especially in the greenhouse. Therefore, you should begin cultivating in the greenhouse when the weather is not that great. If you sow lettuce seeds in a very hot greenhouse for example in August, you may experience that the seeds do not germinate. The lettuce seed will go into hormonal seed dormancy due to the heat. Nature is extraordinary. The seed dormancy prevents the seed to germinate in a climate that is too warm in which the lettuce cannot survive. The hormonal seed dormancy ends when it gets cold and will then begin to germinate again when the climate is more optimal for the lettuce.

Therefore, you should check the temperature in the greenhouse a couple of times, so you get an idea of what the temperature is throughout the day before you sow. The temperature should not be above 25 degrees for longer periods. If that is the case, wait before you begin the lettuce cultivation in the greenhouse.

The easy varieties

If you are a novice when it comes to cultivating lettuce, Spirekassen recommends choosing the varieties that are ‘cut and come again’-varieties. It is for example the frisée lettuce. These you can sow in rows without having to thin out during growth. You can just cut off the lettuce leaves you need, and the plant will make new shoots with new leaves.


Where to cultivate lettuce in the greenhouse

  • Sow in garden beds
  • Sow in capillary boxes (you can easily reuse the old growbags)
  • Sow in pots which can be taken inside the kitchen
  • Sow in large trays and large pots

Good to know

In general, lettuce can survive near freezing temperatures without major problems. There may be individual differences in varieties. Especially iceberg lettuce is cold tolerant and can survive below freezing.

Lettuce must be hardened so it can get used to the cold before it can be cultivated in the greenhouse during winter. Therefore, you cannot put lettuce, that you have bought in the supermarket, in the greenhouse and expect it to thrive and grow.

The origin of lettuce

Lettuce was first cultivated in Ancient Egypt for production of lettuce oil. The oil was extracted from lettuce seeds. Back then lettuce was not seen as a leaf vegetable. Later in 2680 BC people began to cultivate lettuce for the leaves.

Lettuce has also had a religious and medical importance for centuries. Originally Europe and North America dominated the lettuce market, however, in the end of the 20th century the consumption of lettuce had spread to all over the world. From 2017 the production of lettuce and chicory worldwide were 27 million tons of which 56 percent was from China.