Home » Design & Construction

Building a specialist tree propagation facility for woodland restoration

At Coed Talylan, in Bannau Brycheiniog National Park, we are developing a specialist tree nursery designed to produce native woodland trees with beneficial fungal associations.

The MycoTree Nursery combines conventional tree propagation with experimental growing techniques, sustainable construction and the development of locally produced, peat-free growing media.

Our aim is to create a practical, resource-efficient nursery capable of producing trees for woodland restoration while providing facilities for research into mycorrhizal fungi and their role in tree establishment.

The project is being developed with support from the Bannau Brycheiniog Local Nature Partnership, whose funding is helping us establish the infrastructure and equipment needed to begin nursery production.

The nursery comprises a partially submerged propagation greenhouse, outdoor air-pruning beds, extensive growing beds, two caterpillar tunnels, storage facilities and a dedicated composting system.

1. The Walipini: A Dug-in Propagation Greenhouse

At the centre of the nursery is a 6 × 4 metre dug-in greenhouse, known as a walipini.

A walipini is a partially submerged greenhouse that uses the surrounding ground to moderate internal temperatures. The thermal mass of the earth can help reduce temperature fluctuations, potentially providing more stable growing conditions than a conventional above-ground greenhouse.

Our walipini is an experiment in adapting this approach to specialist tree propagation, combining earthbag construction with modern glazing, irrigation and propagation equipment.

Earthbag construction

The greenhouse incorporates retaining walls constructed from earthbags filled with compacted soil.

Earthbag construction uses readily available materials and relatively simple building techniques to create substantial walls with significant thermal mass.

The walls are approximately 350–400 mm thick and constructed on compacted gravel foundations. They retain the surrounding soil, allowing the greenhouse floor to sit below ground level.

The retaining walls will be finished with protective plaster, while drainage and waterproofing measures will help prevent moisture penetrating the structure. As the walls retain substantial quantities of soil, their stability and drainage are important considerations in the construction.

Above the walls, a timber framework supports a sloping roof constructed from 25 mm multiwall polycarbonate glazing.

The greenhouse has been designed to maximise natural light while taking advantage of the thermal properties of the surrounding ground.

We will monitor the greenhouse’s performance to evaluate its effectiveness for propagation, particularly during the colder months.

Internal propagation facilities

The interior is designed to maximise propagation capacity within the relatively small 24 m² footprint.

A combination of tiered shelving and a central heated bench provides almost 25 m² of growing surface.

Rear wall shelving

Three tiers of shelving extend along the full 6-metre rear wall. Each shelf is 600 mm deep, providing a total of 10.8 m² of growing surface.

Front wall shelving

Three tiers of shelving extend for 5 metres along the front wall, leaving space for access. Each shelf is 600 mm deep, providing a further 9 m².

Central heated propagation bench

A central propagation bench measures 4 × 1.2 metres, providing 4.8 m² of growing surface.

The bench incorporates heating to maintain suitable root-zone temperatures during germination and early seedling development.

An automated irrigation system will provide controlled watering throughout the propagation area.

The tiered shelving provides considerable additional growing space, although light availability and access will influence how the different levels are used.

The walipini will be used for seed germination, early seedling development and experimental mycorrhizal inoculation.

In particular, it will provide an environment in which different propagation media and fungal inoculation treatments can be compared.

2. Outdoor Air-Pruning Beds

Alongside the walipini, we are constructing six raised air-pruning beds.

Each bed measures 1.2 × 2.4 metres, giving a total of 17.28 m² of air-pruning growing surface.

The beds are constructed using timber frames supporting a raised mesh growing surface.

How air pruning works

Air pruning is a method of encouraging the development of healthy, well-branched root systems.

When a growing root reaches the exposed underside of the growing medium, the root tip dries out and stops extending. This encourages additional root branching further back along the root.

The process helps prevent the development of long, circling or poorly branched roots.

By encouraging the growth of numerous fine roots, air-pruning systems can produce trees that are better equipped for transplanting.

Our beds will be used to investigate how different growing media and microbial inoculation treatments influence root development.

They will also allow us to compare the performance of trees grown using different propagation systems.

3. Outdoor Nursery Growing Area

The main nursery growing area occupies a fenced enclosure measuring 50 × 30 metres, providing a total area of 1,500 m².

The enclosure will be protected by deer-proof and rabbit-proof fencing to prevent browsing damage to young trees.

A 2-metre-wide access track runs around the inside perimeter, providing access for nursery operations, equipment and the movement of planting stock.

This leaves an internal growing area measuring approximately 46 × 26 metres.

The site is divided into two main growing sections, accommodating outdoor nursery beds, caterpillar tunnels and supporting propagation facilities.

Outdoor growing beds

The main outdoor growing beds are designed for raising young trees to a suitable size for bare-root planting.

The planned growing beds measure:

• Length: 12 metres
• Width: 1.2 metres
• Paths between beds: 400 mm

The layout allows for 29 beds across the 46-metre internal width of the enclosure.

Each bed provides 14.4 m² of growing space.

The total planned growing area is therefore:

29 beds × 14.4 m² = 417.6 m²

This provides a substantial growing area for producing native woodland trees.

The nursery’s initial production will concentrate on our Native Woodland Restoration Pack, comprising sessile oak, silver birch, rowan, hazel, hawthorn and holly.

Based on an indicative planting density of 40–50 seedlings per square metre, the outdoor beds have a theoretical standing capacity of approximately 16,700–20,900 young trees.

Actual production will depend on individual species, growing conditions, spacing requirements and the time needed to produce suitable planting stock.

As the nursery develops, we will refine these estimates based on practical growing experience.

Caterpillar tunnels

Two caterpillar tunnels, each measuring approximately 20 × 4 metres, will provide an additional 160 m² of protected growing area.

These lightweight tunnel structures offer a flexible alternative to conventional polytunnels.

They can be erected and moved relatively easily, providing seasonal protection for growing beds without requiring permanent foundations.

The tunnels will be used for seedling establishment, propagation and growing species that benefit from additional protection during the early stages of development.

They will also provide opportunities for experimental trials comparing growth under protected and outdoor conditions.

4. Irrigation and Water Management

Reliable irrigation is essential for nursery production, particularly during germination and the development of young root systems.

The nursery will incorporate a combination of stored water, gravity-fed distribution and automated irrigation.

The infrastructure includes water storage capacity of approximately 3,000 litres, supplying the nursery’s irrigation system.

Within the walipini, automated watering will allow greater control over the moisture conditions experienced by seedlings and propagation trays.

Outdoor growing beds and caterpillar tunnels will also be supplied through the irrigation network.

Water management is particularly important for our mycorrhizal research, as moisture availability influences both root development and the establishment of fungal associations.

By monitoring irrigation and growing conditions, we aim to develop efficient propagation techniques that make appropriate use of available water.

5. Storage and Working Facilities

The nursery will include a dedicated storage shelter and working area.

This will provide space for the equipment and materials required for tree propagation and nursery management, including seed trays, propagation containers, tools, irrigation components and growing media.

The working area will also support the preparation of propagation substrates and the handling of planting stock.

Having these facilities immediately adjacent to the growing areas will make nursery operations more efficient, particularly during the busy periods of seed sowing, transplanting and lifting bare-root trees.

6. Producing Our Own Peat-Free Compost

A central objective of MycoTree Nursery is to develop a system for producing our own peat-free propagation media.

Commercial horticultural growing media often depend on materials that require significant processing and transport.

We want to investigate how locally available organic resources can be used to produce high-quality growing media suitable for native tree propagation.

The nursery will incorporate large composting bays alongside a woodland leafmould production system.

Woodland leafmould production

We are developing a system of composting cylinders constructed from recycled stock fencing and Mypex membrane.

These cylinders will be located within the woodland and used to accumulate fallen leaves and other suitable organic material.

The material will be left to decompose naturally over approximately one to two years.

As decomposition progresses, the leaves break down into a dark, friable material known as leafmould.

Leafmould can provide an important component of peat-free growing media, improving moisture retention and contributing organic matter.

We will investigate blending mature leafmould with other materials to produce growing media with suitable drainage, aeration and nutrient characteristics.

The woodland also provides other potential organic materials, including naturally accumulated moss and decaying vegetation, although collection will need to be managed carefully to avoid damaging woodland habitats or depleting their organic matter.

Composting and propagation substrates

Large composting bays will provide additional capacity for processing organic materials and preparing growing media.

An important part of the project will be evaluating different compost formulations for native tree propagation.

This includes investigating mixtures containing leafmould, composted woody material, mineral components and other locally available substrates.

We are particularly interested in understanding how these materials influence root development and the establishment of beneficial microorganisms.

Alongside the production of growing media, we will investigate methods for introducing locally sourced mycorrhizal fungi into propagation substrates.

The intention is to develop growing systems that support both healthy tree growth and the formation of appropriate fungal associations.

7. Integrating Mycorrhizal Inoculation into Nursery Production

What distinguishes MycoTree Nursery from a conventional tree nursery is our intention to integrate beneficial fungi into the propagation process.

The nursery infrastructure has been designed to accommodate experimental inoculation techniques at different stages of tree production.

Within the walipini, we will investigate methods of introducing mycorrhizal fungi during germination and early root development.

These include the use of locally sourced fungal spores, cultivated fungal inoculants and carefully controlled trials using woodland soil collected from around established host trees.

We are also developing techniques for propagating arbuscular mycorrhizal fungi using living host plants.

The outdoor growing beds and air-pruning systems will allow us to monitor the subsequent development of inoculated trees and compare their growth with untreated control plants.

By examining root colonisation, growth and establishment, we aim to identify practical inoculation methods that can be incorporated into routine nursery production.

Our longer-term ambition is to supply bare-root trees with verified mycorrhizal associations, alongside fungal inoculants that can be applied during planting.

The development of these techniques is described in more detail on our Mycorrhizal Fungi & Inoculants project page.

8. Sustainable Construction and Resource Efficiency

The nursery is being developed with an emphasis on resource efficiency, appropriate technology and practical experimentation.

Several elements of the design reflect this approach.

The walipini uses the thermal properties of the ground to moderate growing conditions, potentially reducing the energy needed for propagation.

Earthbag construction provides an opportunity to investigate alternative building techniques using relatively inexpensive materials.

The air-pruning beds are constructed using timber and galvanised mesh, creating a durable system for producing trees with well-developed root systems.

The caterpillar tunnels provide flexible growing space without requiring permanent structures.

Locally produced peat-free compost will help reduce reliance on imported growing media, while stored water and efficient irrigation will support responsible water management.

These approaches are intended not only to make the nursery more resource-efficient but also to demonstrate practical techniques that other small-scale nurseries and community woodland projects could adopt.

9. Project Development and Funding

The development of MycoTree Nursery is supported by funding from the Bannau Brycheiniog Local Nature Partnership.

This support is helping us establish the nursery infrastructure, including propagation facilities, outdoor growing systems and associated equipment.

The project is being developed in stages.

The initial construction work includes the earthbag walipini, its timber framing and glazing, internal propagation benches, irrigation and finishing.

Alongside this, we are establishing the fenced outdoor growing area, drainage, air-pruning beds, caterpillar tunnels and supporting facilities.

The composting systems will develop alongside the nursery, gradually increasing our capacity to produce locally sourced growing media.

As these facilities become operational, we will begin establishing the first tree crops and developing our experimental inoculation programme.

The nursery will continue to evolve as we gain experience and evaluate different propagation methods.

10. Learning, Volunteering and Collaboration

The construction and development of MycoTree Nursery also provide opportunities for practical learning and community involvement.

We are particularly interested in sharing experience of earthbag construction, alternative greenhouse design, tree propagation and peat-free compost production.

As the nursery develops, we intend to provide opportunities for volunteers, students and researchers to participate in propagation, nursery management and applied mycology.

The facilities will complement the wider conservation and educational activities taking place at Coed Talylan.

By combining practical nursery production with experimentation and knowledge-sharing, we hope to develop a facility that contributes to woodland restoration while helping others explore the possibilities of fungal-assisted tree propagation.

Follow our project updates to see the nursery taking shape, or get in touch if you would like to be involved.