Shrubs

What this group is

Woody plants that keep their stems through winter and are multi-stemmed rather than single-trunked, ranging here from New Jersey tea at three feet to elderberry and buttonbush at ten or twelve.

The evergreen ones hold their leaves year round: inkberry in the East, and toyon, manzanita, California lilac, and Oregon grape in the West. The deciduous majority drop them, and several are worth as much bare as leafed, which is the whole argument for red-twig dogwood and winterberry.

Why the layer matters

A yard with lawn and a few trees has two vegetation layers. A woodland edge has four, and the shrub layer is where a large share of songbirds nest, where small animals move under cover, and where much of the fruit is produced.

Adding shrubs changes a yard's habitat value more per plant than almost any other decision, and it fixes the design problem of a garden that vanishes in November.

The buying details that decide everything

Three things determine whether a shrub does what you bought it for, and none of them are usually on the tag.

Some species are dioecious: individual plants are male or female, and only females fruit. Winterberry, inkberry, and spicebush are all dioecious, and a planting of females with no male nearby produces nothing at all. Winterberry goes further and needs a male whose bloom time matches the female's, so pairing an early female with a late male fails just as completely.

Others are not dioecious but fruit far better with cross-pollination. Arrowwood viburnum and American beautyberry both do. Two plants beat one, and two genetically different plants beat two copies of the same named clone.

Pruning timing depends on where next year's flower buds sit. Oakleaf hydrangea flowers on old wood and sets its buds the previous summer, so a late-winter cutback removes the entire display. Smooth hydrangea, American beautyberry, and buttonbush flower on new wood and can be cut hard in late winter with no loss. Getting this backwards is the most common reason a healthy shrub does not flower.

Cultivars, and one clear case to avoid

Named selections are convenient and often better shaped than wild forms. Two cautions are worth carrying.

Fully sterile flower forms produce no usable pollen or nectar. A mophead hydrangea in full bloom is, to an insect, an empty display, and the lacecap form of the same species is not.

Purple- and gold-leaved selections of native shrubs have in several published trials been measurably less usable to leaf-feeding insects than the green wild type. Where the shrub is meant to work rather than only to look good, the straight species is the safer purchase.

Sources: Mt. Cuba Center (native shrub trials including Physocarpus, Hydrangea, and Ilex); Doug Tallamy and University of Delaware research on native woody plants, cultivars, and caterpillar use; Lady Bird Johnson Wildflower Center, University of Texas at Austin (species profiles and pollination requirements).