I have different varieties of semi-cold hardy cacti in my new garden:
Some of the plants I have are the following:
Mammillaria nejapensis
Orocereus trollii
Espostoa melanostele
Notocactus magnificus
Notocactus leninghausii
Opuntia subulata
Mammillaria mystax
Mammillaria hahniana
I bought them because the tag said "hardy to 20F"... however, I believe these plants need to be protected from frost anyway... (if by frost we mean below 32F!)
I was thinking about clear plastic circular tubs that are 7 inch in diameter and 9 inch in height. I would put one on each of the cacti to keep them dry during winter and to protect them from the cold winds.
However, I wonder if cacti need ventilation if they grow under these "cloches?" Should I make holes in the plastic to allow air circulating through? But wouldn't these holes defeat the purpose of protecting the plant from the cold?
What else can I do to protect my new cacti this winter? Last winter the temperature went down to 14F for two consecutive nights.