What is the lowest temperature my 7-foot pencil cactus can tolerate here in Chicago?
Lowest Temp Pencil Cactus Can Tolerate in Chicago
Euphorbia's are temperature sensative and will drop leaves and/or segments if they get too cold. I lost heat in a greenhouse last winter with temps at 10*F outside. The greenhouse temp dropped to 22 for one night. All euphorbia's dropped leaves, some perished completely, and the 2 big pencils lost a lot of segments. Any night temperature above 55*F. will be sufficient for your plant.
The plant will survive in temperatures down to 40*F., but will not grow. Any legnth of time under 40*F. on a regular basis will leave you with an unhappy camper.