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Growing Conifers

Conifers for Containers/Hedges

by R. William Thomas

Conifers that you plan to plant in containers should be drought resistant and fully hardy—both the roots and the tops. Root hardiness is the key to successful container gardening with conifers. The roots of container-bound plants are exposed to much lower winter temperatures than roots in the ground. A good rule of thumb: if a plant is listed as hardy one or two USDA hardiness zones to your north, it is probably safe to grow in a container in your area.

Water stress is the other major challenge for container gardeners. Good drainage is essential, as is avoiding drought. Evergreens use water year round, and the soil in the container should never be allowed to completely dry out. This is as true in winter as in summer. Water whenever the soil is dry to the touch, anytime the soil is not frozen. Mulching not only helps reduce water stress but also helps insulate the soil from severe temperature swings.

The easiest conifers to train as hedges are those, such as yews, that resprout on old wood.

The easiest conifers to train as hedges are those, such as yews, that resprout on old wood.

Rot-resistant wood, such as cypress or teak, is the ideal material for containers. It has some insulating properties, doesn't dry out quickly and is not damaged by freezing and thawing. Pots made of plastic, fiberglass and other synthetic materials are resistant to cracking and don't dry out quickly. Concrete has both those advantages and is long lasting, attractive and paintable. Clay and terra cotta are not recommended for winter use in Canada and the northern half of the U.S. because they are easily cracked by freezing and thawing.

The following genera are some of the best choices for containers—especially the shrubby and dwarf plants, which look attractive alone or mixed with flowers and vines.

Conifers for Hedges

Almost any conifer can be trained as a hedge. The easiest ones to use are those that shear very well and resprout on old wood, such as plants in the following three genera:

Cephalotaxus (Plum Yew) Taxus (Yew) Thuja (Arborvitae)

Other conifers that tolerate shearing well but do not resprout on old wood include:

Pines, spruces and firs can be sheared in spring when the new growth has just emerged and is still soft, but not at any other time of the year. For this reason, they are much more difficult to maintain as hedges. If you don't mind the work, though, you can create a very unique hedge using these plants.

R. William Thomas is Education Division Manager at Longwood Gardens, where he teaches several classes on woody plants, including conifers. He is past president of the American Conifer Society and editor of Trees and Shrubs (Hearst Books, 1992).