Like a Straight Answer

[Prospector]

Winter hardy info is hard to come by and what is out there is confusing.

Desert-tropicals.com lists most Lobivias, Rebutias and Echinopsis as not frost hardy.

But the Tucson Cactus and Succulent Society in their 123 care of cactus list, show most of them as hardy down to 18F.

Now 18F is the same in Arizona as it is any place in the world. 18F is 18F.

Both lists agree on the amount of direct sun
Why are they so far off on temps?

So what/which list do you go by?

Thanks

Frank

[stephen.prout@uk]

can i ask a similer question about the uk because ive read that minus temps in the southern states last for just the early morning were as here they can last for most of the day so what plants can i have outdoors in my garden.

[hablu]

The big difference is humidity. Where I live it's up to 80 - 90 % during fall and wintertime. Even now in summer with nice weather today it was above 60%. I don't know about humiditylevels in Tucson. Here it makes that I always have to keep temps above the freezingpoint, whatever deserttropicals says about frosttolerance.
greets Harry

[iann]

The Desert Tropicals hardiness data is both very generic and very approximate but you are also misinterpreting it. Desert Tropicals gives most Rebutias and many Echinopsis as zone 9b (winter lows down to 25F or -4C). This is certainly very conservative, I have overwintered Rebutia seedlings and they have experienced regular frost and occasional temperatures lower than -4C.

Desert Tropicals also gives a minimum average temperature for all species, usually around 50F (10C) which would suggest that a frosty night is only safe when the day is well above freezing. Cacti are certainly better able to take just a few hours of frost between warmer sunny days but there are species, Rebutias included. that can take some frost day and night at least for a while.