Great shrubs

February 18, 2014

Suggestions for shrubs from the Spring 2014 issue of Seasons, the member magazine of The Morton Arboretum.

Shade stars

oakleaf hydrangea (Hydrangea quercifolia)The Japanese maple is seductively lovely. Small and easy to find a spot for, relatively shade-tolerant, with beautiful lacy foliage that turns brilliant red or yellow in fall, the hundreds of cultivars of Acer palmatum are hard to resist.

But Midwestern gardeners may find Japanese maples’ beauty doesn’t come easy, says Kunso Kim, head of collections and curator at The Morton Arboretum. This species prefers relatively acid soil, which is hard to come by in the Chicago region. It needs excellent drainage but steady soil moisture and protection from drying winds. “It’s quite picky,” Kim says.

For a shade-tolerant, garden-sized plant that has all-season interest and beautiful fall color but is not so fragile, he recommends shrubs such as oakleaf hydrangea (Hydrangea quercifolia, at right) or viburnums such as Northern Burgundy™ arrowwood viburnum (Viburnum dentatum ‘Morton’).

If you have room for a larger tree—more like 20 to 30 feet—he would love you to consider some of the interesting but uncommon maples to be found at the Arboretum. The snakebark maples, for example, such as Acer tegmentosum, have fascinating sinuous streaks running down the bark.

He especially loves a group of Chinese and Korean trees called trifoliate maples, whose leaves, made up of three leaflets, are totally unlike the familiar five-pointed shape on the Canadian flag. Among them is three-flowered maple (Acer triflorum), with brilliant red to orange fall color, while paperbark maple (Acer griseum) has handsome coppery peeling bark as well as leaves that turn brilliant scarlet in fall.

Golden rush

ForsythiaWhen golden-yellow forsythias burst into bloom, Chicagoans know winter is finally over.

This shrub earns its place in so many gardens because it’s such a sign of spring and it’s so hardy and long-lived. Once established, forsythia is “pretty resilient,” says Todd Jacobson, head of horticulture at The Morton Arboretum.

The ancestral forsythia species are mostly large shrubs from eastern Asia. But many hybrids and cultivars have been developed that are more compact or more cold-hardy, or bloom in different shades of yellow from pale lemon to deep gold, Jacobson says.

After it has bloomed, a forsythia spends the rest of the season as an unremarkable shrub with deep green leaves on arching branches that give it an overall fountain or vase shape. Jacobson recommends planting it where it will form a background to other shrubs or perennials.

Few pests or diseases trouble a forsythia. Because it blooms so early, the flowers can be nipped by a late frost, but it won’t harm the plant.

The biggest problem with a forsythia is that over time its vigorous growth can turn it into a tangled, overbearing monster. You can tame it, Jacobson says, by pruning out about a third of the biggest, oldest stems each year as needed.

Or take the more drastic step of rejuvenation pruning, which involves cutting all the stems back within an inch or two of the ground. The shrub will grow back, and then you can keep it under control by regularly removing the oldest stems.