Adding year-round interest
If you're after colourful stems in winter, I'd recommend silverleaf dogwood (Cornus alba ‘Elegantissima', Zone 2a), which has green, white-edged leaves and burgundy-red branches, and is 2.5 metres tall and wide.
Many gardeners feel that the deciduous shrub staghorn sumac also adds year-round interest. There are a number of similar species and cultivars available, all of which adapt well to poor soil. One to try is the cutleaf staghorn sumac (Rhus typhina ‘Laciniata'), which reaches three metres tall by four metres wide. But be aware that they sucker quite freely, which I find a nuisance but makes them good subjects for covering banks and slopes. Staghorn sumac has an open shape with fuzzy new branches and large, purple-crimson fruit, providing winter food for birds.
I rather like some of the barberries for all-season beauty. The most popular is probably the Japanese barberry. I grow Berberis thunbergii forma atropurpurea ‘Golden Ring' (Zone 4, 1.8 metres tall, two metres wide). The reddish purple leaves have a yellow-green margin. Its multitude of shiny red berries are very effective in the winter landscape, and its small, very sharp spines make it ideal as a barrier hedge-but tricky to handle. Barberries grow best in full sun, will withstand dry conditions and appreciate a well-drained soil.
I have a soft spot for the Pacific northwest native Oregon grapeholly. Its shiny, holly-like leaflets, fragrant yellow flowers and blue fruit are very pleasing, while its evergreen foliage, which turns bronze-coloured in fall and persists through winter, really makes this a four-season shrub. It does best in moist, well-drained, acidic soil and should, wherever possible, be shielded from the wind and hot sun. Tree expert Michael A. Dirr says (in his Manual of Woody Landscape Plants) that it's severely damaged at –29°C. Mine is usually well covered with snow, which protects it at such low temperatures. Leaves above the snow line burn badly, so in spring I carefully cut them off to make room for the lovely new reddish bronze leaves that quickly appear.
Ideal plants for small gardens/edging patios
There are at least nine cultivars and perhaps another six species to hunt for. Suckering cascades mahonia (Mahonia nervosa, 45 by 100 centimetres) and creeping mahonia (M. repens, 30 by 100 centimetres) seem more tender and would require a higher zone than the grapeholly, which is Zone 5. And being shorter, they're ideal for the smaller garden or along the edge of a shady patio.
I'm not partial to roses per se, but I do find that some of the old-fashioned and wild roses hold four-season interest. Among them is the rugosa rose, which has value both as a specimen shrub and as an impenetrable hedge. It has lovely fragrant flowers, lustrous dark green foliage and large, brick-red hips. The two wild roses I have used in a more naturalistic setting are the Virginia rose and the Northeastern-or swamp-rose. I have always fancied Moyes rose (Rosa moyesii, Zones 5 to 7), mainly for its intense blood-red flowers and decorative four-centimetre-long red hips, but I have yet to grow it.
Two viburnums I recommend are the witherod and the highbush cranberry. The former has dark green foliage, creamy white flowers and berries that change from green to pink, then from red to blue before finishing black; it's not unusual to see all these colours in the same fruiting cluster. The highbush cranberry makes a good privacy hedge, as it can reach five metres high and four metres wide. Its clusters of bright red fruit last well into winter and look particularly attractive when covered by a dusting of snow. Both viburnums are easy to grow in moist but well-drained soil in sun or light shade. In my garden, these plants have proved disease-resistant, but in some years have got quite badly attacked by aphids. An early dousing with insecticidal soap works for me.
Photos: Rugosa rose in spring, summer, fall and winter. Ernst Kucklich (spring), Aleksandra Szywala (summer), Ernst Kucklich (fall) and Marilynn McAra (winter).