The real challenge here in Denmark is not just the cold, its certainly also our damp, gray winters. Lack of sunshine and surplus of water in the form of fog, rain and rain is by far the most limiting factor. This actually goes for both our summers and winters!
For some of the most cold hardy, northern species I have developed a simple solution. A roof, made of thin plastic used for polytunnels provides the plants with a rain cover borth during the winter but also during the summer and despite the fact that the sides are open, the temperature in the summer are raised a few degrees, enough to provide the plants with much better conditions. The perfect ventilation also reduces the risk for any evil fungus attack, an otherwise common cause of cactusdeath here.
The plants chosen for this project are mainly very northern species of opuntioids from Canada, northern US states, pediocacti and some Escobaria vivipara forms. Also forms of Echinocereus from Kansas, Oklahoma and Colorado are tested here.
Very simple setup!
Opuntia fragilis from Illinois.
Opuntia fragilis from Minnesota.