Thuja hedges: why they are now failing in gardens

For decades, they have been a familiar feature of many terraced-house gardens and suburbs: perfectly straight, dark-green Thuja hedges used as an inexpensive privacy screen. Yet these former garden favourites are now failing in large numbers. Experts warn that the issue goes beyond “just” dried-out branches, and increasingly advise removing the conifer hedges entirely and replacing them with species-rich alternatives.

How Thuja went from garden favourite to problem plant

Thuja, often called arborvitae, was long viewed as an ideal option: it grows quickly, remains dense throughout the year and is easy to clip into shape. During the 1970s and 1980s, new housing estates acquired miles of these hedges. What seemed to be the perfect privacy barrier is now proving to be an ecological and gardening dead end.

The central issue is that Thuja develops a very shallow root system. During summers with little rain, these roots barely reach the deeper, moister layers of soil. The plants quickly experience drought stress, even where their owners water them regularly.

“Studies show that Thuja hedges can consume up to around 60 per cent more water than mixed hedges containing native woody plants.”

This has long been a concern for local authorities and water suppliers. In several areas, planning rules and local by-laws prohibit or restrict new Thuja hedges. Some places also offer grants towards the removal of old conifer hedges and the planting of more diverse replacements.

Why a Thuja hedge is often an ecological desert

From a biodiversity perspective, rows made up solely of Thuja perform poorly. Their rigid greenery offers birds and insects little food and hardly any varied habitat. There are no flowers and no fruit. For many animals, the hedge is simply of no interest.

At the same time, the dense roots, layer of fallen needles and shade suppress other plants nearby. The soil becomes depleted and is often dry and compacted. Anyone trying to create a border directly in front of or behind the hedge frequently struggles with root competition and a lack of water.

• Hardly any flowers – little food for insects
• No fruit – limited food for birds
• Dense shade – poor conditions for underplanting
• High water consumption – added stress during hot spells

Many towns and councils therefore want hedges that do more: provide shade, retain water in the ground more effectively, supply food and shelter for wildlife, and create a more varied appearance.

The hidden threat to weakened Thuja hedges: beetles

Climate-related stress is compounded by another factor: a longhorn or jewel beetle related to bark beetles that specialises in Thuja. Its larvae find ideal conditions in hedges that are drought-stricken and weakened.

The insects tunnel beneath the bark, damaging the channels that carry water and nutrients. As a result, the plant effectively dries out from the inside, even if the soil may still be moist.

“Once a hedge is heavily riddled with larvae, specialist authorities often consider it beyond saving – there is no effective treatment.”

If a damaged hedge is left in place, it becomes a breeding site and a starting point for further damage in its own garden and neighbouring ones. Other conifers, including certain types of cypress, may also be affected.

Warning signs that Thuja is failing

Garden and tree specialists identify several symptoms that call for swift action:

• Brown patches spreading from the inside outwards
• Branches that dry out but retain their brown scales
• Fine tunnels or hollow spaces beneath the bark
• No new growth on older woody sections
• A hedge that looks dull, open and brittle overall

Arborvitae generally does not regrow from old wood. Once gaps develop, they usually remain permanently. Trying to “rejuvenate” the hedge with drastic pruning generally results only in more bare patches.

When Thuja hedges should actually be removed

Anyone noticing several of these forms of damage should not delay for too long. The sooner a severely weakened or infested hedge is removed, the lower the risk of pests spreading over a wider area.

Specialist bodies recommend avoiding major clearance work and severe pruning during the nesting and breeding season. The period from mid-March to the end of July is generally sensitive, as many birds nest in hedges then. Late summer, autumn or very early spring are often the best times for removal.

“Anyone who is unsure should obtain a brief assessment from the local horticultural authority or an arborist before felling – this helps to avoid problems with wildlife protection and neighbours’ rights.”

Restoring the soil after a Thuja hedge

Once the old hedge and its root stumps have been removed, what often remains is an exhausted, compacted strip of ground. For years, the shallow roots will have taken up water and nutrients there. Replanting immediately can therefore quickly lead to stunted growth.

Anyone wanting to enjoy their replacement hedge over the long term should prepare the soil first:

• Thoroughly remove remaining roots, thick layers of needles and stones
• Loosen the ground deeply and, where necessary, incorporate sand or fine grit
• Work in plenty of mature compost, adding some organic fertiliser too if the soil is very poor
• Leave the strip for several weeks to settle and receive rainfall, ideally covered with mulch

Those with sufficient space and time can sow a green manure crop for a year, such as clover, phacelia or lupins. These plants loosen the soil further and add organic matter.

Thuja hedge alternatives now in demand

Landscape planners now place much greater emphasis on mixed hedges made up of different shrub species. This so-called “living” or “country-style” hedge combines flowering plants, fruiting shrubs and evergreen elements.

Popular components include, for example:

• Laurustinus for winter flowers
• Photinia with red new growth for a splash of colour
• Privet as a classic, pruning-tolerant semi-evergreen choice
• Hornbeam for dense hedges that can be shaped
• Hazel shrubs, providing nuts and cover
• Dogwood and hawthorn for flowers, berries and protection for birds
• Ornamental grasses such as Miscanthus, adding movement and structure

These hedges usually require less water than uniform walls of conifers. Different root depths make better use of the soil, while fallen leaves and flowers bring more life to the garden. Measurements show that species-rich hedges can keep the ground noticeably moist for longer during hot periods.

More variety, more benefits: what changes for garden owners

Moving away from a uniform row of Thuja also changes the look of many gardens. Instead of a strict green wall, a living structure emerges with differing heights, colours and flowering periods. Anyone who values complete privacy can skilfully combine evergreen and deciduous species.

The maintenance work is distributed differently: rather than carrying out frequent, hard shaping cuts across an entire wall, gardeners are more likely to make selective, gentle cuts to individual shrubs. Many amateur gardeners report that they need to prune less overall and gain more enjoyment from watching birds and insects.

Practical tips for changing your own garden

People who want to part with their Thuja hedge often face the same question: where should they begin? A planned approach helps to keep costs and workload manageable.

• Check whether local grant schemes are available for hedge replacement
• Obtain quotes from landscaping companies for large hedges
• Divide the hedge length into sections and replace it gradually if the budget is limited
• Choose plants with different mature heights and flowering times
• Include as many native species as possible – they are resilient and valuable to wildlife

There is an additional benefit: replacing a monotonous conifer wall with a layered mixed hedge also improves the microclimate on the property. Wind is broken up, heat builds up less, and the soil does not dry out as quickly. This can be noticeable, particularly in densely built-up residential areas.

In the long term, saying goodbye to a Thuja hedge benefits not only birds, insects and soil organisms, but owners too: the garden becomes more varied, more resilient in the face of weather extremes and often far more interesting than the old dark-green “fortress wall” of the 1980s.