Mountain Ash trees signal the change of the season

Two trees, more than any others, tell us that summer is coming to an end and autumn is on its way – not with foliage color but with bold and brilliant berries. Both are Mountain Ash trees. One is the true native Western species (Sorbus scopulina). The other, its nearly identical but bigger brother, the European Mountain Ash (Sorbus aucuparia) actually is native to Siberia and Western Asia. Interestingly, it has naturalized here, long enough ago that its landed immigrant status has changed in the minds of most plants people and now is considered a full-fledge arbor citizen.   

If you see these colorful trees this month, their delicate branches sagging with berry clusters in richly saturated orange to red, the only real clue you’ll have as to what you are seeing is the size of the tree. The Western native grows as a large shrub or small tree, to 15 feet in height with an equal width. The European plant can reach 40 feet in height, sometimes even taller, with a spread of 25 feet.

Unless you are digging the plant in the wild or buying it from a nursery which specializes in native plants, it is more than likely you are getting the European Ash. And who really knows? Could it be that seed-carrying fruits went one way or another across the Bering land bridge in the bellies of birds or mammals or the pockets of migrants some 12,000 years ago and, indeed, the plants are the same?

Both have handsome compound leaves made up of 15 or so leaflets. The leaves are reminiscent of the fronds of the Royal Fern (Osmunda regalis). The leaves, olive green above, gray green below, are carried on strong, but not stocky, upright branches that stretch up and out forming a dense oval to round crown. The dark brown bark is handsome, closer to smooth than rugged. As winter approaches, the leaves turn, yellow to red. The fruits, which develop from puffs of creamy spring flowers, hang on into winter.

Mountain Ash trees need good, well-drained soil and some seasonal chill. Actually the best berry set comes in the coldest Northwest climates, spawning the theory that a heavy fruit crop in the mild Puget Sound region heralds a cold winter coming.

Buy plants now, through the winter, to put in the ground upon purchase. A cultivated variety S.a. ‘Cardinal Royal’ has especially large, bright red berries. For a slightly more narrow, upright form, look for Sa.’Fastigiata’. Site the plant where you’ll be able to see it out a window or as you go into or out of your house. And if an errant branch needs snipping off, wait until it sets fruit, then bring it inside to enjoy. It will be as eye-catching in a vase as any flower and will help set the mood for Halloween and Thanksgiving ahead.