Color Changes in Arborvitae

Conifer Chameleons

• Discovered in Australia in 1989, "Morgan" (Thuja orientalis "Morgan") has quickly become popular in home landscaping. During summer, "Morgan" displays typical emerald- or lime-green foliage, but as winter approaches, its leaves mutate into a lovely, deep purple. Then, early spring brings forth a startling copper color. As temperatures warm in U.S. Department of Agriculture plant hardiness zones 5 to 8, "Morgan" regains its summer green. Only slightly more subdued than "Morgan," Fire Chief" (Thuja occidentalis "Fire Chief"), also called "Congabe," boasts bright golden foliage in spring and summer, turning deep red in autumn. A sport of the popular "Rheingold" variety (Thuja occidentalis "Rheingold"), "Fire Chief" is more intensely colored. It thrives in USDA zones 4 through 8. Both of these newer arborvitae varieties remain compact, "Morgan" slowly growing to 3 feet tall and "Fire Chief" topping out at 4 feet.

More Color Shifters

• A few of the smaller western red cedars change foliage color seasonally or with age. "Collyer's Gold" (Thuja plicata "Collyer's Gold"), eventually reaching a height of 4 to 6 feet, features foliage that emerges yellow but becomes bright green as it ages. New growth on "Stoneham Gold" (Thuja plicata "Stoneham Gold"), a 6-foot dwarf, comes in yellow-orange but later turns green. Bronzing in the winter, "Whipcord" (Thuja plicata "Whipcord") starts off with bright green, thread-like foliage and grows slowly to 5 feet tall. All of these hybrids flourish in USDA zones 5b to 10.

Autumn Needle Shedding

• Perhaps belying its designation as evergreen, arborvitae loses older growth during the autumn. Some gardeners fear that their plants are sick when they see a significant shedding of needles at the same time. To tell whether an arborvitae suffers from stress or is just in the midst of the normal fall drop, note the location of the needles losing pigment. If they are in the interior of the plant, blame the autumn cycle. Leaves turning yellow and dropping in patches from the outside of the conifer may signal a disease or insect problem. Save needles from the autumn drop to mulch your garden.

Color-Changing Process

• Most trees show green foliage in summer due to the action of chlorophyll inside the leaves that works with the sun's energy to manufacture simple sugars from water and carbon dioxide. The sugars supply carbohydrates needed for the trees' growth and development. With the shorter days of fall, replacement of the pigment chlorophyll slows. As the chlorophyll supply dwindles, other pigments are unveiled. These new pigments, often in brilliant colors, form in the sap of leaf cells in late summer. For their creation, sugars in the plant must break down in the presence of bright light.