Autumn colour change is nature’s way of preparing plants for winter. As temperatures cool and daylight decreases, trees and shrubs adapt by ceasing to manufacture food through photosynthesis. Thus chlorophyll, the green leaf pigment used to capture sunlight, is no longer needed and breaks down, exposing underlying pigments such as the carotenoids, which result in the brilliant yellow and gold hues of trees such as paper birch and maidenhair. (Another pigment group, called the anthocyanins, produce the reds and oranges of maples and burning bush.)
Gold and yellow fall leaves offer a fleeting but spectacular display, especially when combined with other perennials, shrubs and trees that turn orange or red.
Here are some excellent plants with which to dust your garden in autumn gold; though many tolerate part shade, a sunny site produces the best fall colour. A good foliage show is also triggered by warm days followed by cool (below 7°C) nights. Too much rain dilutes autumn colour, while an early freeze halts it.
Maidenhair tree (Ginkgo biloba)
Height, 15 to 18 m; spread, 3 to 12 m. Average garden soil; full sun; pest-free. Zone 4 (shown at top)
Often called a living fossil because its lineage has been traced back to the dinosaur age, the maidenhair tree has unique, fan-shaped leaves that turn butter yellow in fall. Salt tolerant and pollution tolerant, it’s a handsome large tree for city gardens provided a male variety is chosen, as female trees bear fleshy, foul-smelling fruit. For restricted spaces, the narrowly upright Princeton Sentry maidenhair tree (‘PNI 2720’) is a good choice; ‘Autumn Gold’ has brilliant fall colour.
Paper birch (Betula papyrifera)
Height, 18 m; spread, 12 m. Moist, well-drained, slightly acidic soil; full sun. Zone 2
One of autumn’s loveliest sights is the shimmering white trunk and fluttering yellow leaves of our native paper birch framed against a clear blue sky. To evoke the northern forest, consider planting a Red Sunset red maple (Acer rubrum ‘Franksred’) nearby.
Autumn Joy sedum (Sedum ‘Herbstfreude’)
Height, 45 to 60 cm; spread, 45 cm. Average garden soil; full sun. Zone 2
Many sedums turn yellow in fall, but Autumn Joy is one of the most dependable for seasonal colour, with long-lasting, bronze red flowers that stand out against the pale yellow leaves.
Eastern redbud (Cercis canadensis)
Height, 8 m; spread, 6 to 9 m. Average garden soil; part to full sun. Zone 4
This small, often multi-stemmed native tree is a delight in spring when tiny, pink flowers cloak its dark, low-sweeping branches. Large, heart-shaped leaves open soon after and turn yellow in fall. An excellent choice as a backdrop to other native shrubs such as Fothergilla spp. and oakleaf hydrangea (Hydrangea quercifolia).
Photo, above right: Larch (Larix laricinia)