How does pollarding work? What works well in a permaculture design for harvesting botanical supplies such as bark, flowers, fruit and leaves from trees? Which trees pollard best? In Part 1 of this blog I focused on pollarding as a useful approach, and here in Part 2 I will consider more detail including examples of medicinal trees to pollard.
How does pollarding work?
Pollarding promotes regrowth by removing the upper part of the leading stem or trunk. Repeated cutting of the central leader stem and/or upper branches, forms one or more dense heads of regrowth. This practice of pruning the upper stem and branches effectively maintains the tree in a partially juvenile state. Fresh regrowth may be prolific due to the upsurge in tree growth hormones reaching buds and shoots. In normal growth auxins from the terminal (apical) bud move towards the roots and inhibit cytokinins moving upwards to produce growth of lateral buds. When the leading bud is removed the dormant buds are stimulated by cytokinins from the roots and they start to grow. The new growth produces many shoots and it is common to see very large leaves produced this way.
How about conifers?
Conifers often do not have the adventitious buds which can sprout from the side or under the bark as shoots when the leader is removed. This means that most conifers cannot be easily pollarded although there are exceptions such as ginkgo, juniper and yew. However, some conifers are cut when young and then a new leader may grow up from an existing branch. We discovered this in managing young Douglas fir (Pseudotsuga menziesii), by pollarding above a number of side branches. Yew can be trimmed back to form hedges or ornamental shapes. Ginkgo can be pollarded although much commercial production of ginkgo leaf is based on coppice cultivation.
Are there any disadvantages?
Pollarding is usually carried out once a tree achieves the required height and is well-established. However, pollarding a tree when it is too old can result in failure to grow. And pollarding may not be advisable for trees in shaded areas as recovery may be problematic, forcing the plant to produce long spindly shoots to reach the light, and become stressed. Some trees can produce a multitude of stems which may not be the desired outcome if becoming too crowded so that disease is encouraged.
In choosing height there is a need to consider future harvesting and cutting operations. In lime (Tilia x europea) trees, pollarding may be quite high when placed along a road or track, but be aware that steps will be needed for access above 1.5-2 m. It is not advisable to use a chain saw above head height and this can be a health and safety worry. The height of the first pollarding cut may also be determined by existing branches on a tree, since these will grow more strongly as a result of the removal of the leader (unless also cut back). Although pollarding may look severe initially, a younger tree will soon regrow. In subsequent years, the new growth can be cut back to the pollarded area, or just above previous pollarding cuts.
Shaping a pollarded tree
If the first pollard cut is of a single stem then a number of branches can arise from this point. These branches can then be cut in subsequent years, and the base of each branch will gradually thicken each year. The growth at the top of the stem or the end of each branch from repeated pruning produces a mass of scar tissue, or knuckle, from which new shoots arise each year. Ongoing management involves repeated pollarding on a regular cycle as well as thinning when appropriate or cutting out any dead or spindly branches. To maintain shape there is a need to be able to follow through with a regular cycle of pollarding. If pollarding is not repeated, the branches will just continue to grow larger. The tree may become hazardous due to heavy branches with poor attachment, and this can be costly to put right.
Some medicinal trees to consider
Alder buckthorn (Frangula alnus) – pollarding of the established tree at 1.5 m produces spreading spindly branches in woodland – may be better growth in more light. The branches can be pollarded and harvested after 2-3 years for bark.
Bird cherry (Prunus padus) – pollarding at about 1.5 m produces a few vigorous and upright stems ideal for bark – the tree is also likely to produce side shoots lower down the stem – if pollarding is not repeated it forms a new leader – needs to be cut back every 2-3 years
Elder (Sambucus nigra) – pollarding at 1 m or more in height gives vigorous growth of numerous stems and flowers and fruit are produced in the second year – so pollarding should be carried out every other year.
Hawthorn (Crataegus monogyna) – pollarded at 1.5 m will produced many crossing spindly and thorny stems – needs further pruning and may not be an ideal candidate for pollarding and perhaps better as a hedge cut alternate years to produce 1 year-old stems for flowers and fruits.
Ginkgo (Ginkgo biloba) – pollarded at 1.5 m makes a bushier plant with good leaf production, and in subsequent years whole branches can be pruned out in summer for harvest of leaves.
Lime (Tilia x europea and other species) – pollarding at 2 m produces a well-rounded head of branches which can then be pollarded again to desired shape – but only a couple of our trees started to flower after 14-15 years so we could not establish whether pollarding successful to gain flower harvests.
White willow (Salix alba) – pollarding of an established tree at 1 m produces very vigorous growth and copious stems. Best to thin these stems to avoid overcrowding in the first year, then harvest all in the second year for bark. Less vigorous is violet willow (Salix daphnoides) with more active ingredients in the bark.
Many other trees could be pollarded for medicinal supplies including eucalyptus, horsechestnut, mulberry. You can see more about the medicinal cultivation and uses of individual tree species in The Medicinal Forest Garden Handbook (2020)