By David Salman, Founder of High Country Gardens
I've been gardening in the high desert of New Mexico for more than three decades. And I've gained a healthy respect for the strength and intensity of our sunshine. A shade loving plant in too much sun quickly becomes a puff of smoke. So early on, I found it to be very important to define what sun or shade conditions mean to gardeners here, especially to those who've moved from areas with more benign and less sunny climates.
The intensity of sunshine varies considerably as one moves across the U.S. This is a huge continent with pronounced regional differences in elevation, heat, humidity, cloud cover, and the resulting intensity of the sun's rays. Full sun conditions in Ohio are radically different than in New Mexico. In Ohio, cloud cover is more consistent. Along with the humid, hazy skies, the strength of the sun's rays are greatly diluted by the time they reach the ground, whereas in the high elevation areas of New Mexico, our 300+ days of cloudless skies and lack of humidity and haze fail to dull the strength of our intense sunshine.
Elevation generally has a huge effect on the sun's intensity; the higher above sea level, the stronger the sunshine, and the higher the ultra-violet wavelengths. You don't tan at 7,000 ft. elevation; you burn.