Gardening with Woodchips: What, Why, How and Who?
With permaculture, we can grow plants using imaginative techniques and materials, negating or diminishing the need for synthesised chemical additions to the soil and using nature and the ‘soil food web’ as our guide. Because we need to ‘Observe and Interact’ with what is going on in our system before adding things in, every site is unique and so what works for one person may be ineffective in a different place. However, the beauty of the internet is that we can swiftly gather information about the pros and cons or any particular technique, and then decide for ourselves if it would be useful for our system. Bearing this in mind, this article shall look at one particular soil-building technique – the use of wood-chips – and explore the benefits as well as the possible challenges of inputting woodchips into your design. I will also go over where and who to get woodchips from and low-cost methods of creating them yourself.
What are woodchips?
Woodchips are small pieces of wood, the production of which forms part of a number of international industries whose raw material is trees. They are created to make paper, textiles, wood products such as chipboard, (see for example 1) and, increasingly, fuel, as well as fertiliser in the form of biochar (2) . Since trees come from forests a lot of this industry is involved in destruction of forest habitats. In spite of this, woodchips are generally defined as a “renewable resource” because theoretically you can just plant more trees (3). However, most timber-related industries, though they replant forests they have felled, do so with monoculture plantations which are not supportive to the ecosystems which they replace (2, 3). The FAO estimates that every year, 7 million hectares of “intact forest landscapes” are cut down (4), with 37% of this destruction being to feed the wood products industry (agricultural expansion comes in at a close second as the cause of 28% of deforestation) (5).
With figures such as these, it is important to investigate where your woodchips come from and ensure that using them is not contributing to behaviour with which you disagree. This may be true even if you are following the ‘Produce No Waste’ principle and collecting woodchips which are seen as a byproduct of a different process and would otherwise be dumped or disposed of. A possible example could be the worrying new trend for ‘biochar plantations’, that is, tree plantations which are specially planted so that they can be cut down and burned, supposedly to help sequester carbon in the soil (2). Critics of this trend abound including George Monbiot on this website (2), and although such processes may well create woodchips as a byproduct you may not necessarily want to support them at all, even if it is simply by taking their waste.
Why would I want woodchips in my garden design?
The most common way of using woodchips for gardening is to spread them on the ground as mulch. Mulch is a wondrous substance which can be made from more or less any organic material and provides a multitude of benefits, thus fulfilling the ‘Multiple functions for Each Element’ (5) and ‘Multiple Elements for Each Function’ (6) principles. What exactly are the functions which woodchips as mulch can have? There appears to be a lot of disagreement out there, though most sources seem to agree that they provide moisture retention and shade for your plants (see for example 7). Susan Vinskofski of Learning and Yearning (8) provides a comprehensive look at why you would want to use woodchips, what people say about them and the results of her own research.
“Of all the mulches we’ve used,” she says, “Woodchips are the least forgiving. They need to be used properly, or they can cause disaster” (9).
She makes it clear that the problems of mulching with woodchips come from using them improperly or in a way which causes imbalance with other elements. For example, although woodchip mulch, over time, adds to the nitrogen content of soil and thus provides more nutrients for growing plants, there is a nitrogen deficiency “at the point where mulch and soil meet” and so if you do not plant below the soil then your plants may not do so well. Vinskofski and others (7, 9) talk of making up for this nitrogen deficiency by adding some kind of high-nitrogen substance to the top layer of soil. She recommends blood meal (9) although this comes along with a whole set of ethical questions.
Another ‘problem’ is that woodchip mulch, over time, creates fungal-dominated soil, which some people claim is not as nutritious for annual plants as bacteria-dominated soil. Vinskofski quotes horticulturalist and professor Dr. Linda Chalker-Scott in questioning this contention, saying “basically, all non-grass species are mycorrhizal” (9)
so unless you are growing grass crops then this should not be a problem for you.
Where can I get them?
As mentioned above, woodchip production is a major global industry and as such, buying woodchips which have been specially produced for the purpose of gardening or landscaping almost definitely contravenes the Earthcare ethic in that you probably would prefer to be encouraging biodiversity rather than monoculture plantation-cropping and forest clearance, as well, of course, as the fact that buying the woodchips in the first place represents an energy stream flowing out whereas in all probability you can find other mulch alternatives for free. However, there are also many industries which produce woodchips as waste from which you may well be able to obtain them. For example, you could ask for unwanted woodchips from:
• A local tree surgery service in your area
• A local carpenter, if there happen to be any left where you live
• The management organisation of any public forests or parks in your area, as they will probably be responsible for cutting down or pruning trees as part of the land management, and may well have access to large machines for doing so.
These are just a few options- once you start looking around, your imagination is the only limit. When obtaining woodchips in this way it is probably a good idea to find out what kind of tree they come from (or become skilled enough at recognising the wood that you can tell this yourself) as there are some species of trees whose wood produces chemicals which can inhibit plant growth in some species (called allelopathy) (10) so you will probably want to avoid these. Some of the most common allelopathic tree species are Black Walnut (Juglans Nigra), Ailanthus or Tree-of-Heaven (Ailanthus Altissima) and Fragrant Sumac (Rhus Aromaticus) (10). These species inhibit plant growth in some species but can be good companions for others so it depends on what you wish to mulch with the woodchips. Toby Hemenway provides some useful information about allelopathic tree species and possible guilds in his book Gaia’s Garden (11).
Another concern with the wood you choose is to check that no chemicals or treatment agents have been used on it.
Do it yourself?
If you have a lot of woody material on your site which you would like to make use of, for example if you have been pruning your trees or cutting some trees down, you may also wish to consider converting your own woody matter to woodchips. If you are interested in this option it is important to think about the energy efficiency of such an endeavour, and what is the most efficient way to create woodchips on your site. If you have a woodchipping machine already this is clearly a viable option, though it’s worth considering whether the organic matter created by the woodchips you produce is enough to offset the usage of whatever fuel you use to power the machine. If someone else has a woodchipping machine, for example a local arborist or landscape gardener, which they use anyway for their work, it may be more energy efficient to ask them to chip your wood for you. However, there may well be more effective and beneficial ways to use your wood, which do not involve high-energy-input techniques, for example to create animal habitats (12), to use as firewood, or as part of a hugelkultur bed (13).
So you have a source which will not cause detriment to the environment and you are ready to face the challenge of mulching with woodchips. So what is the best way to use them? Firstly, it is important to remember that, as with any permaculture technique, every site is different and every plant species has its own unique requirements. You may find woodchip mulching in one part of your site does not work, while in another place it does wonders. Susan Vinskofski has these tips for planting with woodchip mulching:
• Spread the woodchip mulch at least 2-3 inches deep
• Plant seedlings in the soil just below the woodchips
• It may be too difficult to move the woodchip layer for seeds which are small or closely spaced, such as carrots (Daucus Carota), beetroots (Beta Vulgaris), spinach (Spinacia Oleracea) and onions (Allium Cepa), so maybe use a different mulch material if you are planning to grow these kind of crops
• Squash (Cucurbita spp.) grow particularly well in woodchips- in Vinskofski’s garden “4 acorn squash plants grown in a woodchip garden produced over 50 squash” (9).
Much room in the chips
Another application of woodchips is to use them for mushroom cultivation. There are many ways to do this, one of the most simple being to simply obtain something which is inoculated with the mushroom spores (spawn) which you wish to grow and ‘planting’ the spores on pre-soaked woodchips placed in a shady spot on your site (14). There are many benefits to growing mushrooms, including adding biodiversity, food resilience for you with a new edible crop, and even the possibilities of bioremediation or cleaning the soil or water on your site (15). For more information you could check out (14) or (16).
Woodchips can be a great mulch resource which can add nutrients to your soil, provide moisture retention for your plants and suppress weeds. However, it seems they are only a useful option – in terms of energy efficiency and environmental protection – if you have a way of obtaining woodchips which are a byproduct of a different process. Since there are many sources like this for woodchips you may well be able to find them in your area. If you do not, remember that there are many other ways of making mulch.
1. Sixta, H (ed), 2006. Handbook of Pulp. Available online here: http://onlinelibrary.wiley.com/doi/10.1002/9783527619887.fmatter/pdf
2. Monbiot, G, 2009. ‘Woodchips with Everything’. Permacultrue News, 25/3/09. https://permaculturenews.org/2009/03/25/woodchips-with-everything/
3. Li, H, 2014. ‘Burning wood for energy leads to debate over its carbon emissions’. Unearthed Mag, 9/5/14. https://unearthedmag.wordpress.com/2014/05/09/burning-wood-for-energy-leads-to-debate-over-its-carbon-emissions/
4. Rainforest Action Network, 2016. ‘How Many Trees Are Cut Down Each Year?’ https://www.ran.org/how_many_trees_are_cut_down_every_year
5. Eliades, A, 2017. ‘Each Important Function is Supported by Many Elements’. Deep Green Permaculture, 2017. https://deepgreenpermaculture.com/permaculture/permaculture-design-principles/3-each-important-function-is-supported-by-many-elements/
6. Eliades, A, 2017. ‘Each Element Performs Many Functions’. Deep Green Permaculture, 2017. https://deepgreenpermaculture.com/permaculture/permaculture-design-principles/2-each-element-performs-many-functions/
7. Pleasant, B, 2010. ‘Building Garden Soil with Wood Mulch’. Mother Earth News, Oct/Nov 2010. http://www.motherearthnews.com/organic-gardening/gardening-techniques/building-garden-soil-wood-mulch-zmaz10onzraw
8. Learning and Yearning, 2010. ‘About’. http://learningandyearning.com/about/
9. Vinskovski, S, 2015. ‘Using Wood Chips in a Vegetable Garden’. Learning and Yearning, 12/4/15. http://learningandyearning.com/wood-chips
10. Reza, S, 2016. ‘Plant Allelopathy’. Permaculture News, 21/1/16. https://permaculturenews.org/2016/01/21/plant-allelopathy/
11. Hemenway, T, 2006. Gaia’s Garden: A Guide to Home-Scale Permaculture. Chelsea Green: New York City, USA.
12. Wild About Gardens, 2017. ‘Log Pile’. http://wildaboutgardens.org.uk/habitats/log-pile.aspx
13. Miles, M, 2010. ‘The Art and Science of Making a Hugelkultur Bed – Transforming Woody Debris into a Garden Resource’. Permaculture News, 3/8/10. https://permaculturenews.org/2010/08/03/the-art-and-science-of-making-a-hugelkultur-bed-transforming-woody-debris-into-a-garden-resource/
14. Bradley, K, 2013. ‘Making a Woodchip Mushroom Garden’. Milkwood Permaculture, 10/1/13. https://www.milkwood.net/2013/07/10/making-a-wood-chip-mushroom-garden/
15. Rhodes, C, 2014. ‘Mycoremediation (Bioremediation with Fungi) – Using Mushrooms to Clean the Earth. A Mini Review’. Resilience, 7/7/14. http://www.resilience.org/stories/2014-07-07/mycoremediation-bioremediation-with-fungi-growing-mushrooms-to-clean-the-earth-a-mini-review/
16. Mushroom Mountain, 2017. ‘Grow At Home: Log and Stump Cultivation’ http://mushroommountain.com/p/cultivation