Apparently tectorum is cold hardy, but does not over winter outdoors in cold climates.
I have been growing it for quite some time, over ten years., in Guelph Ontario, Canada. I'm in a cold pocket ag zone 4b, Canadian classification I grow it in an unheated greenhouse, and it gets cold inside, although a couple of degrees warmer then outside, still very cold. One year had -36C (-32F) several times inside greenhouse. Tectorum thrives, gets huge clumps, and has to be divided almost every two years. So the extra gets planted outdoors. I shouldn't bother. Only had it survive once over winter outside. And even then was a barely survived. Just hung on while inside greenhouse grew like a weed.
Inside greenhouse also is interesting for the so called "evergreen" daylilies. In the greenhouse, they stay green all winter ,and I don't get mushy damaged foliage you get outdoors.
So, what is difference? There is protection, somewhat, from the late season cold spells, as inside greenhouse, only marginally warmer during winter, it is quite a bit warmer as in 4-6 degrees during late freezes. Soil is not as we during winter. Just normal to slightly drier then normal. But at same time the humidity is relatively higher. But a big factor seems to be lack of wind. One of damaging factors for a lot of plants in winter is removal of moisture from plant foliage by winds carrying it off. Plants not able to bring moisture up from ground in cold of winter to replace what wind removes. In some respects this is why deciduous trees loose leaves. They could just as well evolved to produce winter hardy leaves, like hollyhock.
So basically, it is not the cold temperature that is problem in surviving winter.
Still tying to figure out what is going on biologically with the evergreen daylillies. Not totally convinced re moisture loss. But it is not freezing temperature which turns the leaves to mush as seen when they are grown outside.
Chuck Chapman
-----Original Message-----
From: Mark Cook hemerocallis1962@gmail.com [iris-species] <iris-species@yahoogroups.com>
To: iris-species@yahoogroups.com
Sent: Sat, May 9, 2020 2:51 pm
Subject: Re: [iris-species] spring weather
Dennis,
Iris tectorum is quite winter cold hardy, but it does not take kindly to
a severe freeze once it is in active growth. Yours should survive, but
they may pout a season or two.
Mark A. Cook
