Hildewinteras cold hardiness?

    Has anyone tried keeping Hildewintera-echinopsis hybrids in a cold winter storage?

    Can they take the same temperatures as Trichocerus, lobivias & Echinopsis?

    (I think that the limit for low temperatures of storing Ech-hybrids will be approx. - 5 degrees Celsius, what do you think?)

    Last winter, I forgot some no-name Echinopsis-hybrids in my unheated greenhouse. They were predicted for compost. They began to rot and developed a wooly fungus, but one of them didn't show any sign of rotting and survived. I think, the lowest temperature in the unheated greenhouse was about -17 °C. These hybrids stood on the ground of the greenhouse without any watering during winter.
    In this greenhouse, some Echinocereus stood at the upper level and showed pearls of condensed water on their skin in warmer middays, so the humidity was very high in the greenhouse.