Why Thuja Hedges Are Disappearing From French Planning Permissions

Across France, a formerly fashionable evergreen hedge is gradually disappearing from planning approvals, to the confusion of many householders.

Once the standard answer for screening out neighbours, it is now regarded as both a fire hazard and an ecological cul-de-sac. Using local planning regulations, councils are increasingly telling residents that this favoured hedge is no longer acceptable on garden boundaries.

From suburban favourite to planning outcast

For decades, the thuja hedge was synonymous with suburban privacy. Thick, evergreen and quick to create a natural screen, it bordered thousands of plots on post-war housing developments.

There is still no France-wide prohibition on planting thuja. No French legislation expressly bans it from private gardens. However, an increasing number of communes are discreetly ruling it out through their Plan Local d’Urbanisme (PLU), the legally binding planning framework governing local development.

On the ground, the shift looks simple: apply for a tall evergreen screen in your front garden, and the planning officer sends you back to the drawing board.

These refusals stem from a combination of ecological worries, concerns over fire safety, and the decline of extensive hedges planted during the 1970s and 1980s. To local authorities, this once-valued “green wall” is increasingly seen not as an attractive garden element but as a potential liability.

How local planning rules can ban a hedge

The legal mechanism is technical, yet effective. Article L151-23 of the French Urban Planning Code permits a PLU to establish planting requirements, particularly beside roads, along plot boundaries and within new housing schemes. It can therefore require particular plants while excluding others.

In reality, many PLU documents now identify “single-species thuja hedges” as planting to be avoided. This wording is aimed at long, uniform conifer walls rather than isolated ornamental thuja planted elsewhere in a garden.

A householder who disregards the regulations and installs a prohibited hedge may receive a formal notice from the council, be required to remove it, and face a fine. Penalties can be as high as €1,500, although most town halls favour discussion and gradual replacement, particularly where hedges have been in place for many years.

Officials tend to act on recent projects, using enforcement as a last resort once advice and warnings have failed.

The position is more straightforward on new developments. Developers have to comply from the beginning, commonly replacing previous planting schedules with “mixed native hedges” and giving purchasers clear guidance.

Why wildlife campaigners call thuja ‘green concrete’

Gardeners have traditionally appreciated thuja for its predictability. It grows upright, responds well to clipping, and remains green in winter. Those qualities are far less helpful for biodiversity.

Wildlife organisations including the Ligue pour la Protection des Oiseaux (LPO) characterise long stretches of thuja as a “green concrete” barrier. The concern is not so much the tree itself, but its typical use: densely planted, all of one age, and frequently extending for dozens of metres.

When its small, scale-shaped leaves drop and rot, they release tannins that make the ground more acidic. Soil pH in many such hedges can fall below 5.0. At this level, soil organisms are suppressed and numerous wild plants and insects are deterred from establishing themselves.

A mature, mixed hedge can shelter dozens of mammal and bird species, while a wall of thuja offers little but shade and silence.

Research referenced by specialists indicates that a varied rural hedge may support about 35 mammal species, several bat species, hundreds of insects and scores of nesting birds. By comparison, France has already seen a substantial decline in common farmland birds, with approximately one-third of nesting species threatened.

Where every garden boundary in an area consists of the same sterile conifer, wildlife corridors disappear. Birds can perch in the hedge but find it difficult to feed, nest or access varied shelter. Invertebrates, which are essential to pollination and healthy soil, are similarly excluded.

Thuja as a garden fire hazard

Climate change introduces a further concern. As summers become warmer and drier, evergreen hedges around homes have moved up the agenda in fire-prevention strategies, particularly across southern and western France.

Thuja foliage contains thujone, a highly flammable essential oil. Once a hedge has dried out, its compact mass of fine branches and resin-rich scales can ignite extremely rapidly.

Fire experts report that a long, dry thuja hedge can catch fire in under three seconds and produce flames above 800°C.

When positioned close to homes, garages or parked vehicles, these hedges can act as fuses between structures. In windy conditions, they may carry fire along a street frontage, greatly complicating firefighters’ efforts.

Many hedges now raising alarm date back to the housebuilding boom of the 1970s. Often propagated from just a handful of cultivars and spaced every 80 centimetres, they are approaching the end of their 40-year lifespan. Alongside the fire risk, disease is an issue: the fungal pathogen Coryneum is believed to have destroyed a significant share of older hedges.

What if your hedge suddenly appears on the blacklist?

Homeowners who discover that thuja is prohibited in their commune do not usually face immediate removal. Most PLUs are applied rigorously to new schemes or substantial garden alterations. Existing hedges are generally allowed to remain until they die, are removed, or undergo major changes.

Difficulties arise when an owner wishes to lengthen the hedge or replace it with the same species once it has been taken out. Planning controls can then apply in full. Councils may reject applications or make garden grants conditional on planting alternative species.

Local advisers generally promote one main option: replacing ageing thuja rows with a “country hedge” comprising several native shrubs and small trees. This solution addresses fire safety and biodiversity simultaneously.

Replacing a thuja hedge without ruining your garden

Changing a conifer wall into a mixed, living hedge is a substantial undertaking. It normally requires machinery, soil restoration and time. Garden professionals commonly recommend these steps:

• Remove stumps and major roots mechanically to prevent regrowth and create open planting trenches.
• Improve the ground with roughly 50 litres of well-rotted compost for every metre of hedge.
• Apply agricultural lime to raise the pH gradually and offset years of acidity.
• Do not shred thuja cuttings for mulch, because their terpenes may prevent fresh seeds from germinating.
• Take branches to a green-waste recycling centre, or compost them separately over a long period with additional nitrogen-rich material.

After the soil has been restored, councils often advise planting at least four different native species. Typical combinations include:

Species	Main benefit
Hornbeam	Thick foliage for privacy and tolerates hard pruning
Dogwood	Winter-coloured stems and berries for birds
Hawthorn	Flowers for pollinators and thorny nesting cover
Hazel	Nuts for wildlife, light shade and fast growth

Regional and departmental programmes sometimes support these schemes, offering grants per plant for hedges that meet biodiversity requirements. This financial assistance can help households facing the expense of removing dozens of mature conifers.

Pruning rules, bird nesting and the right time to cut

In France, hedge-related discussions often overlap with wildlife-protection requirements. Many gardeners are unaware that strong guidance, and in some cases local by-laws, governs hedge cutting during nesting periods.

Birds generally nest from spring until early summer. Severe pruning at this time can destroy nests, eggs and chicks, potentially bringing wildlife-protection law into play. This is also part of the reasoning behind recommendations for new mixed hedges.

Specialists usually suggest reserving major hedge cuts for late autumn or early winter, ideally between November and December.

Minor trims beyond this period may still be permitted, depending on local regulations. However, extensive reshaping and mechanical flailing are discouraged while birds are breeding. Choosing plants that retain a neat form after one substantial winter cut can lessen the tension between appearance and ecology.

What a ‘country hedge’ really means

The expression “country hedge”, often used in French planning paperwork, can be confusing for urban residents. It does not describe an untidy, uncontrollable thicket. Instead, it means an organised hedge combining native species selected to suit the local climate and soil.

Such hedges are intended to perform several roles: offering privacy, reducing wind, feeding birds and insects, and connecting wildlife habitats through suburbs and farmland. They can be clipped on the garden-facing side while being allowed a looser shape towards the road or open fields.

In fire terms, a mixed hedge generally has a less consistent structure and moisture level than a continuous row of thuja. It can still burn if neglected and completely dry, but fire usually travels more slowly, giving residents and firefighters additional time to respond.

Practical situations for concerned homeowners

Consider a common example: a 30-metre thuja hedge planted in 1985, now sparse at its base and marked by brown, diseased sections. The commune revises its PLU and includes thuja among plants to avoid for new boundaries.

If the owner leaves the hedge untouched, the council may take no immediate action. Yet when it becomes dangerous during storms or sections visibly die, removal is likely to become unavoidable. Replanting with thuja at that stage is likely to be refused.

By arranging a phased replacement - taking out and replanting five to ten metres at a time over a number of years - the owner can retain some privacy while gradually moving to a more robust, compliant hedge. Country-hedge grants may reduce the financial burden.

A different case concerns a new home on an undeveloped plot. In this instance, the rules are clear from the outset: the developer or purchaser submits a planting proposal, and the council identifies unsuitable species. A failure to adapt may hold up project approval or later extensions.

For gardeners in other countries

Although these changes are taking place in France, the argument over conifer hedges extends further afield. In the UK and parts of North America, similar concerns are being raised about uniform evergreen screens and their impact on neighbours, wildlife and fire safety.

Thuja, Leyland cypress and other vigorous conifers can still have a place when used sparingly. The message from French communes is not chiefly about prohibiting a single plant, but about diversifying garden boundaries, checking local rules carefully, and treating hedges as living infrastructure rather than simply green fences.