Pollarding

Have you ever seen trees with knobby limbs, bare of all leaves and twigs? It’s called pollarding.

Pollarding is a pruning method that limits the size of trees and shrubs. Unlike shearing, which trims everything past a certain point, pollarding cuts back all new growth. This stimulates regrowth that will bring it back to full size.

Shortly after pollarding... (Charles01) Public Domain

Pollarding was first done by the Romans and we still use it today. The word pollarding comes from ‘poll’ which refers to the top of the head (as any horse enthusiast knows). To ‘poll’ someone was to cut their hair. [I wonder if polling at the voting booth came from the same root - asking what is inside someone’s head. It makes sense, but I digress.]

Originally, trees were pollarded to provide food for livestock and fuel for winter fires. [Peasants were allotted a ration of firewood and other materials from the king’s trees in something called an ‘estover’. Pollarding stimulates vigorous upright growth, which turns into straight boards for boats and fence material. Thinner upright stems were also used to make baskets and garden bowers. Pretty smart for 2,000 years ago, eh?

…and two years later (Charles01) CC BY-SA 3.0

Which trees are pollarded?

Pollarding is not recommended for all types of trees. Many conifers do not handle pruning very well. Their twigs tend to die back to the branch they grew out of, providing entry points for pests and disease. Yew are one exception. Trees that respond well to pollarding are those that tend to send out shoots quickly, a characteristic called ‘epicormic’, including:

• ash (Fraxinus)
• beech (Fagus)
• black locust (Robinia pseudoacacia)
• common lime (Tilia x europaea)
• elder (Sambucus)
• elm (Ulmus)
• gum (Eucalyptus)
• hornbeam (Carpinus)
• horse chestnut (Aesculus)

• linden (Tilia)
• maple (Acer)
• mulberry (Morus)
• oak (Quercus)
• plane (Platanus)
• redbud (Cericis canadensis)
• tree of heaven (Ailanthus altissima)
• tulip tree (Liriodendron)
• willow (Salix)

When & how to pollard trees & shrubs

Pollarding is normally done annually in late winter. Maple trees are pollarded in summer to avoid bleeding sap. In most cases, each year’s pollard cuts should be just above the previous year’s cuts. Because pollarding large trees involves chainsaws and ladders, this is best left to the professionals. Small trees and shrubs can be pollarded with hand pruners and a tree saw. When evaluating a shrub for pollarding (or other pruning) keep in mind the future desired shape and size as you cut. Where each cut occurs, a mass of new stems will appear.

Advantages of pollarding

In addition to size maintenance, pollarding provides other benefits:

• It reduces the top weight of a tree, which is a good idea in areas with strong winds, or for trees, such as Bradford pears (Pyrus calleryana “Bradford"), that tend to get brittle with age. 
• Pollarded trees tend to live longer than their un-pollarded cousins, as they are kept at a juvenile growth stage.
• More sunlight reaches the ground, encouraging more growth and biodiversity.
• Pollarding can reduce the risk of heavy limbs falling on power lines.

Disadvantages of pollarding

Pollarding is stressful to trees and shrubs and it must be done every year or two, to avoid limb breakage. The sprouts that appear after pollarding are attached weakly to the ‘knob’ and may break off. Mature trees that have not previously been pollarded can be killed by the process if it is done incorrectly. Even healthy trees and shrubs are exposed to pests and diseases after pollarding is done.

Whether you use pollarding or not, now you know what all those knobby looking trees are about!