Growing up I was told mountain ash berries were poisonous. I'm sure the lie wasn't intentional...my family just didn't know any better. They weren't foragers, after all. Realizing I could cook with the berries gave me the thrill of discovery, as did learning that our mountain ash is the rowan of Lord of the Rings fame. It's the little things.
Mountain ash berries (Sorbus americana) are a classic jelly fruit, tart and full of pectin. Our recent snowfall makes this the perfect time to pick them because the berries (actually pomes) sweeten after a frost. If you live somewhere warm, you can put them in the freezer for a few days to make the fruit more palatable.
Raw berries are juicy and highly astringent. They also contain parasorbic acid, which can cause indigestion, but cooking converts this to sorbic acid, which is entirely benign. The cooked fruit makes a not-too-sweet jelly, traditionally used as an accompaniment to meat, but it's also good with cheese, the sharper the better.
As a landscape tree the mountain ash is relatively short-lived, rarely making it beyond 25-30 years old. In a traditional, in-ground garden that might be an undesirable characteristic, but in containers it's perfectly alright. Even long-lived trees need periodic replacement and root pruning in a containerized growing environment. Small white flowers are very fragrant in late spring/early summer, and they attract lots of pollinators to the garden.
Two thumbs up.