Of all the techniques, greenhouse cultivation is undoubtedly the most effective for prolonging the vegetable garden season outdoors during the winter season. Here are some tips for adventurous urban farmers who want to experience greenhouse cultivation in the Nordic country.
A first method is to grow the vegetables in tunnels covered with plastic wrap. Such a tunnel is in fact made up of one or two thin transparent polyethylene membranes installed on metal or plastic hoops – flexible plastic pipe usually works very well – attached securely to the floor or to the container in which we grow vegetables. For example, you can plant carrots, kales, leeks or onions in August, cover them with a tunnel in mid-autumn and then harvest them during the winter, or even, in some cases, in the spring. next.
The polyethylene film lets in sunlight and keeps enough heat at night for some edible plants to thrive even in the dead of winter. The earth absorbs heat during the day and re-emits it at night in the form of infrared radiation, helping to keep the air under the plastic wrap warm enough to prevent plants from being affected by the cold.
Although the snow accumulated on the sides of the tunnel makes an excellent insulator, it may sometimes be necessary to cover the ground at the base of certain more sensitive vegetables with a mulch of shredded fallen leaves or straw to create a second insulating barrier, especially during the very cold periods of winter. You can also install a heating cable on the ground to ensure the integrity of the vegetable plants during the coldest periods of winter.
An ingenious way to grow vegetables in the off-season in a northern setting is to do so under two stacked greenhouses. This technique developed by Eliot Coleman, owner of the Four Seasons farm located in Harborside in the State of Maine, consists in cultivating the vegetable plants under tunnels covered with polyethylene or agrotextile, themselves installed in a greenhouse made of polyethylene more big.
During the coldest winter days, it is then possible to heat the interior of the tunnels using an electrical system. By keeping the temperature slightly above freezing at night, around 5 ° C, you can grow most leafy vegetables, such as Swiss chard, spinach, kale, lettuce, radish and rocket.
However, if you don’t heat up more, it becomes very difficult, if not impossible, to grow tomatoes and cucumbers during the winter months. In this particular case, it is often more profitable and economical to grow edible plants of tropical origin under artificial lighting inside the house or in any other heated building.
In winter, the cold deters pests and significantly slows down the growth of unwanted grasses. In addition, since there is practically no evaporation, the soil remains permanently moist. Although growing in a double greenhouse requires little intervention, however, care must be taken to provide plenty of compost to the vegetable plants when planting.