organic – flowering bean organic gardens

In this interview, I chat to Iain Tolhurst from the UK about using woodchip
on his farm.

I discovered Iain Tolhurst’s work when I Googled Veganic in 2016. Tolhurst grows certified organic food on leased land for a box scheme and farm shop in the UK. He has been growing without using animal inputs such as manures and blood and bone, on just under 20 acres (about 8 hectares) for 35 years. His farm was described in George Monbiot’s 2022 book Regenesis as “a genuinely regenerative, organic system”¹ using no artificial or livestock inputs and creating a space for diversity and wildlife to return.

Tolhurst grows about 100 different varieties of vegetables on his farm. He uses a system of long seven-year rotations and times the planting of the various crops to fit their differing fertility needs. When a plot is at the end of five years, he takes it out of production for two years to build the soil fertility using green manures of legumes and wildflowers to which he also adds ramial woodchip.

It was his use of woodchip that I was particularly interested in when I asked for an interview. Woodchip offers a good addition to the growing toolkit of alternative solutions to using manures, other animal inputs or artificial fertilisers in gardens and growing systems.

Woodchip at Tolhurst Organics

While we are used to seeing woodchips around fruit trees, on ornamental perennial beds and in forest gardens, using it in vegetable beds often raises questions about nitrogen lockup and soil health. Nitrogen lockup can occur when a carbon-rich material, such as woodchip, creates an imbalance in the soil. However, Tolhurst agreed to the interview as he wanted to highlight the potential of using woodchip in horticultural growing systems.

At Tolhurst’s farm, they use woodchips in various ways; as a propagation substrate, a seedling mix, applying it directly to the plots to build fertility and as a weed suppressant on pathways in tunnel houses. However, he explains, the key to the system working and avoiding nitrogen lockup, is to use different forms of woodchip, appling it correctly, and timing the harvest of the woodchip.

Tolhurst sources the woodchip for the farm from local arborists and it comes from a mix of trees, usually from local gardens. Using local material also reduces the carbon footprint of transport, an issue with many fertilisers. Tolhurst explains that the woodchip is very different from wood shavings or sawdust, as using these would cause issues as they are difficult to compost.

Woodchips and composting

Once the woodchip arrives on the farm, it is composted in a long pile called a windrow. This is turned four times in the first year, after which it is applied directly in the tunnel houses as compost.

To make a seed-raising mix, they also keep some of this composted woodchip and continue composting it for another six months to two years. At this stage, it becomes very crumbly and there is not much visible woodchip left. They then grade it and add a little vermiculite. In Tolhurst’s experience he says, it acts as well as any peat-based material. Finding an alternative to peat-based material has been important in their search for alternative fertility-building materials, especially in potting mixes.

Ramial woodchip

Ramial woodchip is an exciting development in growing systems and growers are experimenting with its use. Ramial woodchip is chipped branch wood sourced from branches less than 7cm in diameter and excludes any wood from the tree trunk. The reason for using chipped branch wood is it has a lower carbon-to-nitrogen ratio than trunk wood and, as the chip is applied fresh, it retains many of the tree’s nutrients and energy in the chip.

Tolhurst explains that he uses ramial woodchip in very modest amounts and adds this into the green manure phase of the growing system. Because they are in the UK, most of their ramial woodchip is harvested in winter and this works well as many of their indigenous trees are deciduous.

At Flowering Bean Organic Gardens, we are exploring using ramial woodchip from introduced deciduous trees and may experiment with some branches from native non-deciduous trees. Not scientific, but certainly a fun to experiment to see what happens in our growing system.

A mixed cover crop that has had ramial woodchip added for fertility
Flowering Bean Organic Gardens

Woodchips on pathways

The other application of woodchips at Tolhurst Organics is the more traditional use of woodchips on pathways. The advantage, Tolhurst explains, is that the woodchip suppresses weeds and adds fertility as it breaks down and the fertility moves across into the beds carried by microorganisms. They lay it about 7cm thick and it reduces weeds for about 2 to 3 years before it is topped up again.

Spot the worm! Woodchip pile full of worms at Flowering Bean Organic Gardens

Talking to Tolhurst and learning more about the innovations on his farm, was certainly inspiring and I know there are many here in Aotearoa trying out new systems and ideas in both commercial and residential gardens. I hope this interview inspires and provides an introduction to the huge topic of using woodchips for fertility.

Happy gardening and growing!

Monbiot, G. (2022). Regenesis. Allen Lane ↩︎

Further information

For anyone wanting to do a deep dive into using woodchip in gardens and farms, I found the Woodchip Handbook, A Complete Guide for Farmers, Gardeners and Landscapers by Ben Raskin and published by Chelsea Green Publishing had lots of great information.

Don’t forget to always consider your safety when working with woodchip and compost materials. Here are some links to more more information about protecting your health when working with composting material.

Toi te Ora Public Health Protect yourself from Legionnaires’ disease when gardening

WorkSafe Legionnaires’ disease and legionellosis

What are perennials?

Perennials are plants that grow for more than two years and, while we often think of perennials as trees and shrubs, some vegetables are also perennial. Perennials can be evergreen and keep their leaves all year round, or herbaceous, i.e. their tops die down in winter and their roots stay alive and come away in spring.

Why plant perennial vegetables?

In the garden, perennial vegetables offer some advantages over annuals. Once planted, you rarely need to disturb the soil which means soil life and microorganisms can do their thing while you nurture the plants above the soil and harvest their goodies. Perennials also provide habitat for animals as you are not replanting and disturbing them as often. Some perennials can survive long dry periods as they have deep root systems so the plants are better adapted to tap into deeper stores of water in tough climate times.

Designing with perennial vegetables

Decisions in the garden are continuous. However, initial planning design for perennials is important because some, like asparagus, you may have for 20 years or more.

One of the best bits of advice I have had is to consider water needs when planting perennials. Perennials generally require less water than annuals, so if you group annuals together it allows you to target your water use towards them and less on the perennials.

Perennials often require less maintenance, so they can be a little further away in areas you visit less often, such as the boarders of your garden. However, it is also wise to check whether they have the potential to take over a space and so require a bit of thought before planting.

Asparagus pushing through the soil surface

Mulching, weed control and fertilising

Perennials benefit from a good mulch. Mulching adds nutrients, helps retain moisture in summer, reduces leaching from heavy rainfall and reduces weed competition. Some perennials can be cut back and used as a mulch, which also returns some nutrients back to the soil. Asparagus fronds are a good example, they can be chopped and dropped in place when they turn yellow in late autumn. You can read more about mulching here.

Weeds can be hard to eradicate with perennials as you don’t want to disturb and cut the roots of the plants trying to pull out deep rooted weeds. Weeds can also get well established before you notice them as you tend to check perennials less often than annuals. Getting to the weeds early and providing a good layer of mulch can both help with weed control. Although I must admit, my asparagus seems to be surviving the onslaught of weeds that I never seem to get to!

Perennials do need feeding, especially when you are harvesting from the plants. Well made compost and mulching increases organic matter and both help feed your plants. I also use a good quality seaweed fertiliser.

Some perennials can be cut back to provide compost materials. For example, once the Jerusalem artichokes have finished flowering and die back, I prune them down and use them as a carbon source in my compost.

The lush growth of asparagus in summer with
flowering jerusalem artichokes in the background.

Sourcing perennial vegetables

Perennial vegetables are not always easy to source, but the search is worth it. Most of our perennial vegetables have come from specialty stores and some from friends. We grow asparagus, sorrel, jerusalem artichoke and New Zealand spinach. Some plants are available in general garden stores, but it is worth looking at online specialty growers and definitely your friend’s and neighbour’s gardens.

Dividing perennials and sharing them around serves two functions, keeps you and your friends supplied in plants and also stops overcrowding.

Happy gardening

Tag: organic

Woodchip to build fertility