Urban trees planted in poor quality soil using a method inspired by a Japanese botanist return higher survival rates than standard approaches, which could make it more cost-effective to establish trees, according to new trial results.
The ‘Trees Outside Woodland’ project, a partnership led by The Tree Council, Defra, and Natural England, with Kent County Council, Chichester District Council, Cornwall Council, Norfolk County Council, and Shropshire Council, seeks to identify cost-effective methods that could be adopted by local authorities to increase tree canopy cover in England.
Jon Stokes, Director of Trees, Science & Research at The Tree Council said: “In the first three years after planting, the survival rates of young trees in urban areas can be very low. We therefore set out to test alternative planting methods to see if we could identify practices which improved survival rates and which made trees less vulnerable to issues such as vandalism. Solving this puzzle is key to helping local authorities deliver successful and cost-effective tree planting, unlocking all the benefits that urban trees have to offer. One of the methods which we trialled was the Miyawaki method”.
The Miyawaki method, developed by Japanese botanist Dr Akira Miyawaki, involves high density planting in specially prepared soil. It has had great results in Japan, where it was first used to plant trees in the 1970s. However, when this project began, in 2020, it was almost unknown in the UK. This project has tested the approach’s viability and cost effectiveness compared to standard planting methods[i].
The Trees Outside Woodland project planted 16 different trial sites across four local authorities, with a variety of native tree and shrub species planted densely at 3-5 trees per square metre in prepared and enhanced soil, alongside a control plot using more typical planting methods.
Trial sites with public access were chosen, such as recreational parks, with characteristics such as high air pollution, below average tree cover, or high levels of deprivation, where trees could make a real difference.
One of Kent County Council’s trials, at Park Wood, is in an open recreation area that was previously a builder’s yard, with contaminated soil from construction waste, such as sand and bricks. Analysis in 2024, following establishment of the plot in 2021, reported a very high 99% survival rate in the area planted using the Miyawaki method. Today, the trees resemble a dense thicket, with some trees reaching 15 ft and providing habitat and food for birds, and have suffered no vandalism at all. In comparison, there is a good 82% survival rate in the control at this site, but visibly slower growth with trees at waist to shoulder height and having suffered from having stems snapped.
As Rob Thomas, Kent County Council’s Cabinet Member for Environment, said: “I am thrilled that KCC is among the first to trial an adapted version of the Miyawaki tree planting method, and that it has been such a success for Kent.
“The trees that have been planted by the Miyawaki method have proven to be fast-growing, resilient to the stressors of urban areas and are boosting our local ecosystem.
‘I look forward to working with Defra, the Tree Council and other partners to see what the future holds for the Miyawaki method in Kent.”
Across all the 16 trials, the average cost of the Miyawaki method was £9.66 per survived tree, against £50.32 for standard planting methods. This reflects the greater survival rates across the trials of the Miyawaki methods, with a 79% survival rate compared to 47% for the standard planting methods.
The Miyawaki method is a relatively intensive way of planting trees, but these trials indicate that it can be a very effective tool to establish young trees in areas facing challenges such as poor soils and vandalism.
Natural England Chair Tony Juniper said: “There are many good reasons for having more trees in our towns and cities. Native deciduous species support wildlife, such as insects, birds and bats, and bring shade in summer while letting in light in winter. Trees help combat air pollution and enrich green spaces to promote mental health benefits. All of that adds up to huge social benefit and invites the question of how we can support local authorities in getting more trees close to where most of us live.”
“This study is looking for answers and the results will help inform future decision making to increase successful and reliable young tree establishment and protect newly planted trees so that they grow and thrive in local areas and provide benefits for generations to come.”
This project will monitor these trials until September 2025, after which further research will be needed to understand how they perform over the longer term.
[i] Standard planting methods here means the standard approach taken by the four participating local authorities for planting in these sorts of settings. There was therefore some variation in the exact method used, but it was typically pit or notch planting into uncultivated ground at a density of one tree per square metre, mulched and watered when planted.
- Read the full report recently published on The Tree Council website.
- The Trees Outside Woodland project is a 5 year, £4.8 million R&D project, funded by HM Government’s Shared Outcomes Fund.
- The project is exploring novel ways to reduce the costs of tree planting in our cities, towns and countryside and increase the supply of locally produced, biosecure tree stock through a series of ambitious pilot studies. This will support efforts to tackle and mitigate climate change, tackle biodiversity loss and promote greater health and wellbeing by establishing trees within communities.
- The project is a collaboration between Defra, The Tree Council, Natural England, and five local authorities in England.
- The Miyawaki method trials form one part of the project’s Urban Tree Establishment pilot. This pilot also investigated the relationship between trees and utilities and trialled natural colonisation methods in urban areas. Ongoing trials are investigating the effects of the individual elements that make up the Miyawaki method.
- Read more information on the Urban Tree Establishment pilot.
- Read more information on the Trees Outside Woodland project.
