How Free and Plentiful Woodchips can Help Your Organic, Earth-friendly – and Peat-free – Garden Grow

Mounds of woodchips are everywhere nowadays, they’re free for the taking – and they can help you go peat-free. Inspired by a pioneering vegan-organic vegetable grower, I’m now coveting every fresh mound of chips I find.

By John Walker. Published in The Telegraph, 23rd January 2016

have developed a more than passing interest in those mounds of fresh woodchips you see piled up along roadsides and on embankments. These are the pulverised remains of the shoots and branches of trees and shrubs deemed too puny to turn into useful firewood. This brash, which can’t be left lying around, is fed into large, noisy shredders, which spew it back out as chips of various sizes. The piles are bright and noticeable at first, but gradually fade and sink as nature begins its reclamation work. In 12-18 months you’ll have a job even finding them again.

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Fresh woodchips are light in colour and easy to spot, but soon darken as nature begins to reclaim them.

My growing interest in woodchips is driven by my insatiable gardening curiosity: they’re just sitting there, free for the taking, so what could I do with them? Shredded prunings make a great weed-blocking mulch when spread over the soil around permanent plantings (aim for 1-2in/2.5-5cm deep), so that’s one option. Sappy summer trimmings are a good source of “greens” to go into a compost bin or heap (they’ll help a big hot heap to cook). But what else? On excavating a roadside heap that, several months before, had bloomed with a wonderful crop of toadstools, I unearthed dark woody crumbs, coated in fungal hyphae, with a divine, earthy scent. Not long after that, a serendipitous visit to an innovative market gardener nudged the penny through the slot.

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Locally sourced and peat-free compost based on woodchips at work in Iain Tolhurst’s propagation greenhouse.

Iain Tolhurst (“Tolly”) has been an organic grower for 40 years. Tolhurst Organic Partnership, near Whitchurch-on-Thames in Oxfordshire, grows seasonal vegetables on two acres of the Hardwick Estate. Tolly is a pioneering grower who is constantly refining and testing his growing methods. Today, the fertility of the market garden’s soil is generated almost entirely within the holding itself, making the whole growing process a kind of “closed loop” – the epitome of the joined-up approach taken by savvy organic gardeners.

Closing the loop has been crucial to Tolly’s goal of growing not just organically, but vegan-organically, meaning that no animal inputs of any kind – manure, dried blood or ground-up hooves and bones – are used to grow his crops.

Soil fertility is maintained by growing some of it, in the form of sunshine-harvesting green manures which are dug back into the soil, and by adding lashings of home-made compost, of which, as we all know, there is never enough. But all that all changed when a local tree surgeon asked Tolly if he could make use of the chipped remains of trees and shrubs which would otherwise go (for a fee) to landfill sites. As trailer-loads of woodchips began turning up, Tolly set about working out what to do with them.

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As piles of woodchips cool down after their initial hot and steaming phase, fungi soon move in coating the chips with pale mycelium.

First, he lines them up in big windrows roughly 6 x 10ft (2 x 3m) tall and wide. They soon heat up, releasing plumes of steam. As they gradually cool down, they’re turned, a couple of times in summer, then again in winter. The heat is released as micro-organisms start breaking the chips down. When the heaps cool, and the woodchips turn darker, they’re soon invaded by fungal mycelium, and flushes of toadstools often appear.

All of this is nature doing its stuff – transforming complex organic materials into something which can be used again. At the start of his growing career, Tolly made the easy mistake of incorporating fresh sawdust into the soil, which starved it of nitrogen and damaged the crops, so he knew that woodchips needed time to get them ready to use.

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Fresh woodchips, with added shredded leaves (top), and how they look 18 months later after fungi have begun their work.

Digging into a windrow after 18-24 months brings up handfuls of dark, sweet-smelling chips with a distinctive ‘mushroom’ aroma. To make a sowing/potting mix, Tolly uses a ½in (1cm) mesh sieve to gather the finer crumbs, which he mixes three parts woodchips to one part perlite, plus some lime (and an organic fertiliser if needed).

This gives a low-input, home-made compost, made with free, locally-sourced materials that are unlikely to be contaminated by pesticides (trees aren’t usually sprayed). Only the lime and vermiculite comes from outside the loop, and he’s looking for something more local and less energy-intensive to replace the latter. This mix is used to fill multi-cell trays for raising crops for transplanting later. Matured woodchips are also used as soil improver for Tolly’s fields and polytunnels, where they’re spread over the surface and gradually become incorporated into the soil. Now you know why I covet those roadside heaps.

Now I’m busy experimenting – sieving out the crumbs from some older woodchip heaps to use in my own DIY potting mixes. I’ve had success with a 50:50 mix of mature leaf mould and worm-worked compost from my “cool” dalek-type bins. Plants grow like mad, but hungry feeders can quickly exhaust the food supply, and the pots become quite lightweight as they dry out. I’m deploying the matured woodchips to add bulk and have now settled on a basic mix comprising one part each of leaf mould, compost and sieved woodchips – it looks like a winner to me.

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Any non-thorny woody prunings which will pass through a garden shredder can be stored and matured, ready for garden use.

Roadsides aren’t the safest places to forage for your garden’s fertility, so I’m keen to take a tip from Tolly and corner my own home-grown woodchip supply. I’m using a 3ft (90cm) tall and wide mesh cage (like those used to rot down leaves). Anything woody (but not thorny) that’s passed through my electric shredder goes into this. A repurposed “builder bag” would also do the job nicely. If you’re thinking you’ll never have enough material to make it worthwhile, ask the neighbours (or a tree surgeon) to donate their prunings/shreddings. You can add to your stockpile anytime; I have willow and hazel that need trimming right now. Shredded conifers can go in, too (much of the raw woodchip Tolly gets is from vanquished leylandii). If you prefer to cheat, you can bag up fresh woodchips whenever you see them.

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Toadstools bloom on piles of fresh woodchips as fungi set to work on breaking them down.

As your hoard grows, it will get hot inside; the bigger the heap, the hotter it gets. I’m not planning to doggedly turn mine; there is nothing to kill off in woodchips, such as weed seeds, so they can be left to quietly do their own thing.

I’m expecting to see toadstools at some point, as fungi begin breaking down the woody fragments, but that’s nothing to worry about, and they’ll gradually sink as they age. Once the cage is full, I’ll leave it alone for at least 18 months (there’s no need to cover it) before sieving it. The only hitch I can foresee is that once the first cage is full, I’ll be itching to build and fill another.

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4 Responses to How Free and Plentiful Woodchips can Help Your Organic, Earth-friendly – and Peat-free – Garden Grow

  1. Susi Batstone says:

    Excellent! Have you ever tried adding symbiotic fungi to the wood chip piles or mulch? Stropharia rugosannulata (garden giant, wine cap) assists the decomposition and formulation of glomalin, is of benefit to many crops as root assistant and protector, and fruits with big, edible mushrooms!

    Regarding thorny trimmings – roses, hawthorn, bramble and blackthorn – no good to shred? Bonfire best option?

  2. John Walker says:

    Thanks, Susi. No, I haven’t quite gotten around to it; by the time I do wild fungi have usually staked their claim. But it’s a solid idea: grow edible mushrooms at the same time as turning woodchips into compost…

    Since I write that article I’ve been having success with composting down green brambles passed through an impact (i.e. noisy) shredder, so I’m keen to extend that to other thorny material. The worst you can do with thorny material is shred it and then stack it out of the way, where it’ll be a home for wildlife while it’s thorns are gradually blunted by decay.

    Frankly, for me a bonfire in the garden is the very last resort. We should be putting woody material (thorny or not) to much better use, not polluting the air with wood smoke that’s really not good for anyone’s respiratory system. Avoiding bonfires is good for hedgehogs and other wildlife, too.

  3. Colin Hynson says:

    I’ve been offered a pile of woodchips and I was thinking of using them as a mulch around my raspberry canes. I have difficulty controlling grass and weeds growing around my raspberry bushes. I have cut the canes back and then pulled up as much grass as I could. I now want to scatter the woodchips to stop the weeds/grass coming through. Does that sound like a good idea?

    • John Walker says:

      That sounds fine, Colin. Aim for at least a 2in (5cm) deep layer of mulch, but try and keep this away from the actual bases of the canes (i.e. don’t swamp them in deep mulch). You might not eradicate all the grass, but it should be weakened by the mulch layer and you can gradually ease it out – loosen the roots first and get them out, too.

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