I have grown a few different species of these, and have so far been kind of disappointed by the lack of good fall color, even though I have seen trees in other gardens and in photos that colored quite well. I wonder if anyone can recommend a particular variety that might excel in this category?
Buy in autumn dress. 'Joseph Rock' is usually pretty good. As always, site conditions will affect results as well as genetic makeup of seed-raised plants. Exposure can be important, the same specimen turning reddish in sun but only yellow if shaded enough. One often sees vine maples back in the woods not coloring like those on the edge of the road, although this phenomenon is far from uniform. Elsewhere on Camano we have fairly large vine maples planted some time ago that seldom color at all well, the fact this species seems to be essentially absent as a wild plant from the island might be a hint. However, they certainly grew well here, after being planted - we are also getting spontaneous seedlings in recent years.
Fall is a good time of year to visit the Brian O. Mulligan Sorbus Collection at the Washington Park Arboretum, Seattle, to see what different kinds look like. It is easily found and accessed, right off of Arboretum Drive, with several parking areas nearby. To produce a listing that includes "Japanese and Chinese rowans" that have succeeded in UK collections, go to rhs.org > plant finder, type "sorbus agm" into the search box.
Thank you Ron & Michael. I vividly recall seeing that Sorbus collection at the Arboretum many years ago - in fact that was probably what motivated me to plant this tree. I guess I need to make a fall trip to appreciate the autumn show.
The only Sorbus I've got here is alnifolia, which has a reputation for developing very nice color. I've even read some articles that list it as a top 10 tree for fall color. This is its 6th or 7th fall since planting, and it has yet to produce nice color. Its growing in full sun with loamy sand soil on the acidic side. Its a very nice tree, but fall color thus far has been disappointing. I think Ron's advice for buying in fall is very good. I just purchased a native Carpinus after seeing its spectacular color. The other one I have was purchased in spring and has rather drab color.
My experience with S. alnifolia is exactly as you describe. Not only that, but it suffers from rust or some such fungal disease to a far greater extent than the other varieties I have grown.
On the other hand, street tree planting of S. alnifolia in Mt Vernon, WA (near Camano Island, in the next county to the north) has produced showy displays of numerous fruits in fall. There are many others planted in Seattle, where I have not noticed a particular problem with foliage diseases on that species myself. The dominant one here, of course, is naturalized, even weedy S. aucuparia which vastly outnumbers all others on local properties. As with certain common rose cultivars, variation between sites is seen, with a scablike condition immediately noticeable on some individuals and not others. With planting of Rosaceous plants generally the potential is always there for bugs or blights to develop; apart from inherent susceptibilities most popular groups have significant problems in existence just because they are popular, plenty of material being around to support abnormally high levels of their pests and pathogens to build up.
Ron, I've seen some attractive sorbus planted as street trees in downtown Mt. Vernon, but I don't think the one's I noticed (near the R.R. tracks & I-5) were alnifolia.
This is nice colour on three Sorbus alnifolia catty-corner from me in Vancouver's West End. I'm including a close-up of the leaves and fruits from summer two years ago. I was so excited to have guessed the ID back then, and the Parks Board and a posting in the forums confirmed it for me.
