JARS v62n3 - We Learn Something New Every Day

We Learn Something New Every Day
E. White Smith
Portland, Oregon

After having a real nice three-week stretch of warm sunny weather in late February and early March, we then went back to the cold rainy weather that we like so well here in Oregon. During the week of April 5th we had some light frost here at our nursery, but the frost often did not bother us too much because we have lots of overhead tree cover which protects the plants and flowers. I was out cutting trusses for the early Portland Chapter truss show and had about twenty good ones so far when I was walking down to the greenhouse to see if there were any vireyas in bloom that I could use.

The path to our greenhouse is in open sky so everything along it had been damaged by frost, except for Rhododendron aureum (was named R. chrysanthum at one time) which was in bloom. I cut a nice truss and went on to the greenhouse. Then I got to thinking, why didn't aureum have frost damage? Something is going on that I had not noticed before? Okay, R. aureum is native to the Siberian-Mongolian mountains and Manchuria, south to Japan and Korea - cold harsh places. In my mind, maybe or probably, this species has adapted to the cold by not letting its flowers be damaged by frost and cold. Badly frosted flowers probably can't set seed and that is the only reason the flowers are there, right? If plants of R. aureum are to survive over millions of years it needs an extra advantage which I think is flowers that resist a bit of frost. Oh sure, bad frost will get them, but... Also this species blooms over a long period of time which also would be a big help in the plant's ability to set seed.

I can't think of any other species rhododendron that has flowers that can survive frost in an open sky area. The flowers of R. mucronulatum , which is closely allied to R. dauricum , certainly can't survive frost, but they bloom over a long period of time so they do get a chance to set seed. I am thinking that R. aureum must have special genes to protect its flowers.

I learned another thing that same week. A big plant of R. macabeanum was blooming for the first time, and as I walked by it earlier in the week I thought I should get an umbrella and tape it to a stick and put it over the truss to protect it from the frost that was coming. But I didn't do it. What a shame. I did cut the truss for the early truss show even though it had been frosted. It was a perfect truss with very large leaves, the best I have ever seen on a macabeanum . Three weeks later the truss sitting in a vase on our front counter still looks good, except for the frost damage. And we are still learning.