Re: sunlight tolerance

 

The sun is stronger as the sun approaches a vertical position overhead (zenith). It only reaches the full zenith in the tropics (exactly where in the tropics depends on the time of year). As you go farther from the tropics, the sun's intensity actually becomes less, thought the number of daylight hours, of course, increases further north during the summer. Clear and/or thin air increases the intensity of sunlight independent of location of the sun in the sky. These considerations do influence how much direct sun an iris can tolerate. In it's native northern habitat, Iris setosa grows in full sun but here in California I give it some afternoon shade.

I don't recall if I have ever scorched I. tectorum leaves, but I have to be quite careful of I. japonica, I. confusa, and I. wattii. At least on hot days, they cannot take full afternoon sun here.

Ken Walker
Concord, California USA

On 4/28/2015 11:40 AM, Yana Maltais y*@shaw.ca [iris-species] wrote:
 

From my limited knowledge of sun rays and angles, there is the issue of the further north one is the stronger the sun in the summer.  My area also hits 40 degrees at times in the summer.  Although not super cold in winter, less these days than previous decades.  -15 C for short periods is usually the coldest now.

Yana


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