Seems a zone 8B at 24.8F would be the min.These usually form a subterranean caudex, So with a dry bed during the winter months maybe a little lower.

This a link to the article you were referring to,I have never tried this but some people say this helps?Anyone here tried this?

12' x 12' x 8'Actually looks better from the inside, This was constructed of all recycled materials, (even the lumber came from a neighbors scrap pile...

Hottest here in Central KS was 48.3C , 119F in 1936Back in the "Dust Bowl Days"Last year seemed to avg. low 90's Great weather for outdoor planted P...