Part 2: Care and maintenance of trees in small spaces
In part 1 we focused on species selection and planting in small spaces. But what can be done for trees already established in the ground? Is it possible to limit the ultimate size of a tree once it is planted? Let’s find out about care and maintenance of trees in small spaces.
Care and maintenance of trees in small spaces – a long-term commitment?
Unfortunately it’s not possible to stop a living tree from growing. But the good news is that there are practical techniques to limit and reduce the size of trees; even very mature specimens can be gradually reduced to a more practical height over the course of several years, and proactive upkeep of newly planted trees can enable them to be retained at a manageable size indefinitely.
However prevention is better than cure, so we recommend opting for species and spacings that are appropriate for your site at the outset rather than taking on a commitment to regular pruning which may not be sustainable over the lifespan of the trees. The following information should be treated as applicable for existing trees rather than as NHS Forest’s recommendations for long-term maintenance of any new trees that we are supplying for planting on healthcare sites.
Pruning to Restrict Tree Size
Selective pruning is the best way to manually control the size of trees, improving their health, shape, and appearance. This method – sometimes called ‘crown reduction’ – decreases the height and spread of the canopy, increases airflow and sunlight penetration, and reduces susceptibility to wind damage.
For most native deciduous species pruning should be undertaken in the early winter months after the leaves have fallen and the trees are dormant (the main exception to this rule of thumb are species prone to fungal diseases; to reduce the risk of silver leaf it is important to prune productive fruit trees and Prunus species such as bird and wild cherry in mid-summer). With the exception of dead branches, trees should never be pruned when they are just starting to produce leaves in the spring.
Pruning can begin as soon as the trees have been planted. Aim to shorten the lateral growth and create a more open form, focusing on diseased or damaged branches. Much like a human haircut, you should aim to leave the tree looking its best with a balanced and even distribution of branches on all sides. Removing lower branches will allow access for mowing, mulching and enjoying the shade of the tree.
Pruning is best attempted in stages, evaluating the effect on the aesthetics of the tree. It is prudent to prune a little and often before excessive growth becomes a problem as heavy cutting can put trees under unnecessary stress, particularly if removing more than 25% of the canopy at a time.
Unless a tree is already severely damaged, avoid ‘topping’ it by indiscriminately removing its upper parent branches. While this may instinctively feel like the most immediate way to restrict the height, indiscriminate heading cuts leaving only the smaller lateral branches creates an unnatural look and can be detrimental to the tree, reducing its sturdiness and increasing vulnerability to pests and diseases.
When removing branches with a diameter exceeding 10 cm or if pruning a tree will require extensive use of ladders, it would be sensible to consider employing a professional arborist.
Pollarding is an intensive method of pruning that may be used to keep trees smaller than they would naturally grow; it is an annual process requiring trees to be recut to maintain their pollarded form. Pruning in this way permanently changes a tree’s shape resulting in a distinctive outline with twiggy regrowth radiating from the cut branches and an enlarged ‘pollard head’. The technique can be applied to both young and mature trees but is not suited for all species as some may produce hazardous regrowth that can break off and fall to the ground.
Pollarding can be considered where a tree has outgrown its allotted space, retaining a consistent height and span. It can also be used to reduce shading or to create clearance from overhead cables. A professional arborist will be best placed to advise on suitability for specific trees.
Coppicing is another type of pruning where a tree is cut to ground level to facilitate regeneration of new stems from the base, coppicing creates a multi-stemmed shrubby plant without a trunk. It is commonly used in hedging to increase the density of foliage. Maintaining a coppiced tree will require regular recutting and will result in a permanently change to the form of the tree; as such it would be prudent to consult a professional arborist before undertaking coppicing, particularly if the trees are well established.
Growth Regulating Compounds
Growth regulators are products containing synthetic hormones used to influence the development of plants. Specialist formulations for trees are applied to the soil at the base of the stem to be absorbed by the roots. It’s important to check concentrations carefully as even very small amounts can have a significant impact – we suggest consulting an arboriculturist if you are unsure.
Using growth regulators will not stop growth entirely and does not eliminate the need for other maintenance – but slowing development for a couple of growing seasons can help newly planted trees to establish, reduce the need for pruning and watering, and could be considered as part of the wider strategy for keeping trees to size in their early years post-planting.
Replacing Felled Trees
While some are long-lived, no tree can live forever and there will be situations where felling becomes necessary because a tree has become a safety hazard or is unsustainable due to its location or condition. If replanting in the same location it will be necessary to remove as many of the roots and other residual material as possible to avoid depleting nitrogen in the soil and may harbour pests and pathogens from the previous tree.
Consider which species will be better suited to the available space (see part 1 of this blog for some smaller native trees) or whether planting in another location may be more sustainable. Depending on the size of the tree that was felled, the 3-2-1 rule may be used for a recommended number of replacement trees to replant; (at least) 3 replacement trees for a large tree, 2 for a medium-sized tree, and 1 for a small tree.
Relocating Mature Trees?
It is possible to transplant established trees of almost any size, but the process is often costly, labour intensive and comes with no guarantee of success. Trees suffer stress when uprooted, and the loss of too many roots in the course of relocation may even kill a tree outright. Although this could be considered for particularly unique and treasured specimen trees, NHS Forest generally does not recommend this approach.
Thank you for reading about the care and maintenance of trees in small spaces, and just a reminder that we have fully funded tree bundles available for NHS sites in England. This includes the Urban mix – our smallest multi-species bundle specifically for sites with limited space for planting. For more information or to request tree bundles for your site please visit our tree planting page.