Would you like to winterise your greenhouse? It is almost always a little warmer inside than outdoors – but it will only remain permanently frost-free if the greenhouse is heated. Good insulation and air circulation are indispensable. Here are the best tips for successful overwintering.
Until around mid-December, your potted plants will be fine even in simple greenhouses – provided a heating system maintains the minimum temperature for sensitive plant species. As you can imagine, however, this turns into expensive fun in the long run. In a winter-proof greenhouse, on the other hand, the Mediterranean plants will get well into the next year with reasonable heating costs.
Winterising the greenhouse: Insulate with film
The classic solution is a barrier made of insulating film (wrap). The insulating skin is usually attached to the inner skin of the house using special fastening clips. The film is available on rolls of different widths to cut to size yourself or as a complete set including fixing material especially for individual greenhouse models.
Attached to the inside, the film is protected from sun, wind, hail and frost. When attached to the outside, it can bridge slight leaks in the greenhouse. A tarpaulin made of one piece protects it from the weather. If mainly deciduous plants are overwintered, it does not necessarily have to be translucent.
Winterise the greenhouse: Insulate the floor
The greenhouse is insulated with foil, the plants do not stand directly on the ground, and every hole in the cover, no matter how small, has been plugged. And yet it is still uncomfortably cold underfoot inside? Then it would make sense to also permanently cover the foundation with insulating panels (for example Styrodur). This also saves heating costs.
To do this, uncover the foundation all around, lay the boards and fill in the soil again. Lightly cover the upper end of the boards with some soil. If your house stands on a wall base, it should be insulated at least during the winter months. If necessary, also from the inside – for the sake of a nicer appearance.
Ensure good air circulation
Always keep things moving! This is especially true for the greenhouse air. This is because a steady breeze prevents stagnant, moist air, which promotes the outbreak of fungal diseases.
An ordinary heater without a fan creates a certain amount of circulation, but only as long as it is running. However, the warm air collects mainly at the top, while oleander and co. may keep their “cold feet”.
A fan heater distributes the heat more evenly – it transports the warm air from the ridge to the ground. In a winter-proof greenhouse, it is best placed low (for example on a low greenhouse table) and in the rear third of the house – with due distance to the insulating foil.
How to keep your plants standing well
Even a small house has room for dozens of potted plants. They no longer grow now, and many receive a light pruning or are tied together before wintering. They can therefore stand pot to pot. In addition, lower potted plants can be placed on their edges.
If air can still pass through the crowns, even a third tier is conceivable. The lowest tier stands well on disposable pallets, which are sometimes given away free of charge by DIY stores. Underneath, the air can circulate, which limits the formation of mould and other fungal diseases.
Another advantage is to place a layer of insulating boards made of rigid foam on the pallets – this helps against cold feet.
Sick plants must stay outside
Pests in the winter quarters, such as aphids, scale insects and spider mites, can take their toll on potted plants. There they also manage to colonise previously healthy plants – although not as quickly as in summer. Moreover, they have practically no enemies under glass. Before putting them in the greenhouse or at the latest before closing the doors of the winter-proof quarters, it is therefore advisable to take a close look at each plant. Then treat infested plants with approved agents (for example, with rapeseed oil preparations).