Suggests Jeremy Prescott

Trees are amongst the jewels of Dulwich - but there is a dilemma about planting them. Whilst well-chosen trees do not cause problems, put it in the wrong place and within a few years a raft of fiercely tree-protecting rules and bureaucracy kick in, which can cause prolonged misery and cost for the planter or - more likely - their successors.

What are the rules?

The regulatory system is unhelpfully asymmetrical - no licence is needed to plant, but rafts of protections apply thereafter.

If you are in Southwark’s conservation area, as much of the Dulwich Estate is, permission is required for all work on trees over 7.5cm diameter at breast height - that’s just 3 inches in old money, a tree of perhaps only ten years old. “Work” includes removal. Permission is always required for work on trees subject to a tree preservation order. More information and an application form is on Southwark Council’s website.

Householders within the Dulwich Estate’s Scheme of Management require additional, written permission (by way of a licence) for work on all trees other than fruit trees, shrubs or seedlings, with no size specification. More positively, the Scheme’s Tree Consultant is available to provide advice - free of charge - on householders’ trees, including pruning, shaping and the selection of new or replacement trees.

What’s the problem with trees?

The sub-soil in Dulwich is heavy clay, which shrinks in dry periods. This can cause subsidence - normally in very long dry spells during the summer months - and structural damage which can be aggravated by tree transpiration and root activity. Other problems include damage to or blocking of drains, particularly older drains with poor seals, and physical damage such as lifting and falling branches or structural failures of the trunk. Shading and overhanging can also be an issue.

The RHS rule of thumb is that soil drying for high water demand trees will extend outwards to a distance equivalent to the height of the tree, and perhaps half of the height for intermediate or lower demanding trees. Root systems can extend much further.

Tall hedges can also contribute to soil drying, where it is suggested that the height of the hedge is kept below its distance from the building.

Choosing new trees

In choosing a new or replacement tree, do please make sure that you are aware of its mature size of and choose one appropriate to the space available in your own garden - and you need also to consider the impact of the fully-grown tree on your neighbours and their properties. Unless you have a larger garden, “forest” trees such as oak, beech, horse chestnut, cypress, ash and plane, all with large branch and root systems, should be avoided, as should eucalyptus, willow and poplar trees which have extensive, water-seeking roots that can seek out and access drains, and all high-water demanding trees (most of the foregoing).

Advice on what trees (and hedges) to consider is available from Dulwich Estate’s helpful Tree Consultant, from garden centres (but do read the label and do your own research as well) and from the RHS. Please make sure your garden designer is abreast of the issue. Google “RHS trees for smaller gardens” for practical advice and considerations (height and spread/season of interest/lowering/fruiting/foliage/colourful stems or bark/weeping, particular locations, containers) and an extensive range of specific ideas.

Tree, hedge and building issues?

Issues with trees and subsidence can prove a nightmare, involving your own or your neighbours’ insurance companies, tree experts and the protecting bodies, and disputes with neighbours.

A now departed neighbour of ours planted a Dawn Redwood (metasequoia) about 15 feet from our property. Only discovered in China in the 1940s, it was a popular tree in the 1970s when I suspect he planted it. It’s now 20 metres high with a wide - and widening - buttress. Specimens in cultivation have grown to 40-45 metres so far with the potential to grow to even greater heights, 60 metres (200 feet) being mentioned. It’s the sort of tree whose label the now departed neighbour cannot even have glanced at.

The Society encourages residents to plant trees, which are very much help preserve Dulwich’s heritage and reputation - but please do choose and position them with care.