Why Are Evergreens Evergreen?

By Joanne K, Extension Master Gardener Volunteer, Pitt County Extension Office

Year-round evergreens form the bones of the garden whether as trees or shrubs thanks to the wide variety in their sizes, shapes, and textures. In winter, evergreens are even more prominent providing structure, color, and visual interest in the landscape when few flowers are blooming and deciduous trees and shrubs are bare.

Why are evergreens green in winter?

Tough evergreen needles are coated with a waxy layer allowing them to conserve moisture so that they lose less water during dry periods. Evergreen needles are actually hollow tubes with internal pores that can resist water loss. The small surface area of the needles also reduces moisture loss.

Japanese Plum Yew, Cephalotaxus harringtonia - Yews are noted for their soft needles unlike the usual prickly conifer needles.

During the winter, evergreen growth slows down but doesn't stop. Thanks to the retained moisture, they make chlorophyll all year and stay green. Chlorophyll allows them to produce sugar in winter protecting tree cells from freezing in cold temperatures. This is because sugar with other components lowers the freezing point of water in the cells providing that protection.

Evergreen conifers do lose their needles gradually since they only last about 2 to 5 years. The older needles turn brown or yellow when they are shaded out by new growth at the branch tips. Since the dying needles are close to the trunk, the trees always look green thanks to the new growth at the branch tips.

Broad-leaf evergreen plants like hollies have a thick, waxy covering called the cuticle. This coating has several layers that help to form the shiny, leathery texture and thorny spines of holly leaves. The cuticle also reduces water loss helping to prevent the leaves from freezing.

Burford Chinese Holly, Ilex cornuta 'Burfordii' - This tough holly cultivar tolerates heat, drought, and poor soil.

Dwarf Yaupon Holly, Ilex vomitoria, 'Nana' - Vomitoria refers to the practice of Native Americans using the leaves to make a vomit-inducing beverage to purge and purify themselves.

This frost protection allows holly leaves to photosynthesize to produce food and stay green during the winter. Hollies may also curl their leaves when the temperatures drop to preserve moisture and resist drying winds.

Thanks to their dense growth evergreens are also particularly valuable in winter for the survival of wildlife like birds and small animals. They provide shelter in their dense foliage from adverse weather and predators and food when other sources of nutrition are scarce. Photosynthesis releases oxygen and removes carbon dioxide from the air.

East Palatka Holly, Ilex x attenuata, 'East Palatka', Native - Its bright red berries are both ornamental and food for birds.

Hollywood Chinese Juniper, Juniperus chinensis 'Kaizuka' - Junipers can be tall trees, small shrubs, or ground cover.

Holly Tea Olive, Osmanthus heterophyllus - The sweet fragrant flowers of Osmanthus appear in late fall to early winter.

Western Arborvitae, Thuja plicata, 'Green Giant' - This evergreen doesn't have needles but soft, flat foliage with overlapping scales.

By adding evergreens to your landscape you'll enjoy year-round beauty and structure in your garden while benefiting the environment as well.

All of the evergreens pictured can be seen in the Walking Garden at the Pitt County Arboretum. All photos are by Joanne K.