Thuja hedge: specialists warn of serious consequences for gardens

The mood is now shifting: specialists are warning of serious consequences for gardens.

In many residential areas, a familiar sight is currently disappearing: dark-green walls of arborvitae are developing gaps, turning brown and dying back bit by bit. Once seen as the ideal solution for screening and marking property boundaries, they are proving problematic for water management and biodiversity in a changing climate. Agronomists and landscape architects are now speaking with surprising clarity: the era of the Thuja hedge is ending – more quickly than many amateur gardeners wish to admit.

How the Thuja became a garden favourite – and why it is now failing

The classic Thuja hedge was perfectly suited to the housebuilding boom of the 1970s and 1980s: inexpensive, fast-growing and dense throughout the year. Anyone wanting privacy could order 20, 30 or 50 plants, place them in a row, and their green wall was complete.

That very concept is now working against the shrub. Thuja has one major weakness: its root system remains extremely shallow. During prolonged dry spells, it can barely access water from deeper layers of soil.

Specialist bodies report that Thuja hedges can draw up to around 60 per cent more water than hedges made up of native woody plants – a genuine problem, especially in summer.

Anyone who spends days each year standing beside the hedge with a hose, only to see brown patches appear regardless, experiences this dilemma first-hand: high water consumption, yet no dependable privacy screen.

Why the green wall is an ecological misstep

Alongside the issue of water, there is another, less obvious concern: the ecosystem behind the hedge. Compared with mixed or native hedges, Thuja is regarded as almost “lifeless”.

• Hardly any insect species use Thuja as a food plant.
• Its dense, uniform foliage provides suitable nesting sites for only a small number of bird species.
• Soil beneath old hedges is often depleted, compacted and lacking in life.

Many local authorities are already responding. A number of development plans now include restrictions on hedges consisting solely of Thuja, and in some cases new planting is effectively prevented. Some towns and councils even support their removal by offering grants for taking out old Thuja rows and planting diverse, “living” hedges instead.

Stress, beetles and total failure: what is now tipping Thuja populations over the edge

As drought becomes more frequent, these already thirsty hedges come under severe stress. Weakened plants release chemical signals that practically attract pest insects. One particularly troublesome example is a specialised boring beetle that targets Thuja and related species.

Its larvae enter beneath the bark, tunnel through the plant’s conductive tissue and thereby interrupt water transport. From the outside, this may initially look like harmless browning in isolated areas, while the process is already advancing rapidly within.

Once a Thuja hedge is heavily infested with boring beetles, specialist bodies consider the plants virtually beyond saving – no reliable treatments are available for the concealed larvae.

Affected shrubs then die slowly “from the inside out”. Brown sections spread, shoots become brittle and gaps develop, until eventually more dead material than living green growth remains.

Reading the warning signs: when a Thuja hedge has no future

Many garden owners hope for a long time that their hedge will “somehow recover”. However, there are clear warning signs for which specialists advise a radical solution:

• large brown patches that move from the inside outwards
• shoots that are completely dried out but still covered in brown scales
• visible feeding tunnels beneath the bark when the upper layer is lifted
• no fresh growth at all on older, woody sections

One key issue is that Thuja produces virtually no new growth from old wood. Once a gap has formed, it will generally remain permanently. A hedge that once provided full privacy then turns into an uneven patchwork.

Anyone wishing to avoid depriving birds of breeding sites should choose the timing of removal carefully. Authorities recommend avoiding extensive removal of woody plants during the main breeding season – roughly from mid-March until the end of July – wherever possible.

How to remove Thuja hedges properly – and restore the soil

Once the decision has been made, considerable work lies ahead. The hedge should be removed completely rather than simply cut off close to ground level. The root stumps also need to come out; otherwise, the soil remains densely threaded with old roots that hinder new plants.

After digging everything out:

• Loosen the soil deeply and break up compaction.
• Work in plenty of mature compost or well-rotted manure.
• Allow the ground to rest for several weeks so that its structure and soil life can stabilise.

In many cases, it is worthwhile raising the soil level slightly with loose soil, particularly on heavy, compacted clay soils. This helps new woody plants establish their roots more easily and reduces waterlogging after heavy rain.

Suitable Thuja replacements: living alternatives for privacy screening

Landscape gardeners now advise mixed or natural-style hedges almost unanimously. They may be a little less perfectly straight, but they are more resilient to weather extremes and considerably more valuable to wildlife.

Examples for a mixed hedge

Plant	Characteristic
Laurustinus (Viburnum tinus)	Semi-evergreen, with white flowers in winter and spring
Photinia	Red new foliage, year-round privacy screening
Privet	Tolerates pruning very well and is popular with birds
Hornbeam	Tolerant, retaining some brown leaves for winter screening
Hazel	Nuts for squirrels and birds, with an open growth habit
Dogwood species	Colourful bark and berries for birds
Hawthorn	Thorny, ideal protection for birds and rich flowering
Miscanthus & other ornamental grasses	Break up the appearance, gain height quickly and need little maintenance

Such mixed hedges do not have to be planned rigidly. Three to five species are enough to create a far more resilient mini ecosystem. Many of these woody plants need less water and can shade the soil more effectively.

Measurements show that natural, diverse hedges can retain substantially more soil moisture during heatwaves than a dense belt of Thuja – in some cases around one third more.

What a new hedge offers the climate, wildlife and neighbours

Saying goodbye to a row of Thuja can be difficult for some garden owners, as it was considered a dependable, neat privacy screen – hardly any fallen leaves, few flower remnants and a crisp edge. The good news is that a well-planned alternative brings benefits in many areas.

Mixed hedges:

• store more CO₂ through their differing growth forms
• supply insects with pollen and nectar from spring through to autumn
• provide nesting places and food for songbirds
• break the wind more effectively because they do not act like a solid wall
• protect the soil from drying out and erosion

For neighbours, a varied hedge can even be more pleasant because it lets through more light and appears less imposing. At the same time, privacy remains intact when species of varying heights and dense growth habits are combined.

Who benefits most from the radical approach

Anyone living in an area affected by recurring water shortages, watering bans or strict garden-design requirements should assess their Thuja hedge realistically. Older stands that are already weakened use a great deal of water while no longer delivering reliable privacy. In these circumstances, consistent removal may even make more economic sense than investing every year in watering and emergency pruning.

The hedge is also often the biggest opportunity for people who want to adapt their garden more closely to climate protection and biodiversity. Rather than relying on a single conifer species, replanting creates a structurally varied zone that positively attracts small mammals, birds and insects.

There is another point that is frequently underestimated: children learn far more about nature from a living hedge that flowers and bears fruit than from a monotonous conifer wall. Anyone who sees their garden in future as a small habitat rather than simply a demarcated plot will take more pleasure in the new hedge with every season – and will eventually not miss the old row of Thuja.