Rethinking Sun Tolerance
Reprinted from the 1994 Eugene Chapter newsletter; condensed for publication in the Journal
I consider 9 to 5 to be full sun because that is the most sun that I can get in my garden. I was very interested to see what plants did take full sun after I cut down four oak trees.
All the information I can find indicates that Rhododendron auriculatum , 'September Song', 'Frank Galsworthy', 'Swamp Beauty', 'Ivory Ruffles' and 'Exbury Calstocker' all need some afternoon shade. The plants mentioned above did not burn a leaf or turn yellow (except those about to fail anyway). Even 'Tweety Bird' had full sun from 9 until 2:30. One leaf scorched because I didn't have enough water on it, but the rest have very dark green leaves.
How can this be? After thinking on the subject for some time now, I have come to the conclusion that most rhodies will take full sun if they are planted so that they are well drained and get plenty of water. Why I say this is because the first rhodies I planted were in poor draining clay soil. If I watered them sparingly, even if they were sun tolerant, they had burned and scorched leaves. The next year I watered them well and some died from overwatering in the poorly draining soil. That is why I now put plenty of cedar bark in the soil when I plant them. If they get enough water they don't burn and I have no problem with the roots rotting.
There is nothing scientific about this information, but I truly believe that the way a plant is planted and cared for will make the difference whether it will take full sun or not, with a few exceptions.