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Using Woodchips in Allotment & Garden

This email from a newsletter reader raises the question of how best to use woodchips on an allotment. Woodchips are a really useful resource but you need to use them properly for best effect.


Woodchips used to cover paths between raised beds.

On my allotment we have access to fresh wood chips and there is disagreement about how best to use them. I advocate spreading it on paths that are slippery and letting it decompose there for a few years before using as a mulch. I’m a no dig gardener. I’ve found that if a pile of wood chip is up hill from a veg bed the run off will make the crop suffer… lack of nitrogen I think.
Some gardeners want to dig it in to the clay soil after a season in a pile just thinking to improve structure, but I am worried about what else it will do the the life in the soil
I’d welcome your opinion

Woodchips Carbon Nitrogen Ratio

I use wood chips a lot, can’t get enough of them, but you do need to keep in mind that they are very high carbon but low nitrogen. The C:N ratio is usually around 500:1. This means that they can be useful in composting as a brown if you’ve a surplus of greens – but use frugally because of the super-high carbon.

This high carbon means they are great for paths. Their decomposition sucks in nitrogen which means most weeds and grasses just can’t grow. Some deep-rooted weeds may be able to grow through them if they’re already established.

Once decomposed and no longer actively sucking in nitrogen they become a humus rich material which can be used as a mulch or soil improver.

Back to Eden

You may have heard of ‘Back to Eden’ gardening which is basically growing through a mulch of woodchips. Obviously this retains water and prevents weeds growing. Having sat through a video on the subject, I noted that it was mixed with chicken manure which is very high in nitrogen.

There are some claims that a woodchip mulch sucks little nitrogen from the soil as only the base is in contact with the soil. I admit I’ve not tried it but that’s because I find it very hard to believe.

Woodchip Compost

I’m quite interested in regenerative agriculture and follow Richard Perkins videos about his permaculture farm in Sweden. This year they’ve had a load of compost made from woodchips which he’s quite pleased with if only because of it helping to retain water in their drought. They grow on a no-dig method adding 5 cm of compost to their beds each year.

Adding decomposed woodchip compost to the soil, whether clay or sand, will improve it by adding humus. A pure woodchip compost will be low in nutrients but humus alone is a benefit to any soil.

Improving Clay Soils

I believe the key to improving a clay soil is most often increasing the pH. The addition of lime improves flocculation – the formation of particles – which makes the soil more friable and open.

Adding partly decomposed woodchips to a clay soil will eventually improve it so long as the clay isn’t so solid as to form an anaerobic layer above it, preventing decomposition. As the woodchips decompose they will be utilising available nitrogen so the soil will be depleted with a negative effect on plant growth. Quite what the effect of removing nitrogen from the soil’s eco-system would be I don’t know but I can’t see it being beneficial.

I did find adding large amounts of turkey litter beneficial to a clay soil. This is effectively small woodchips or large particle sawdust which is mixed with nitrogen rich droppings. It was added as a 20 cm layer in the bottom of a trench above forked open clay sub-soil. The topsoil being replaced over the litter.

So my opinion is that adding partly rotted woodchips to the soil will, at best, have a negative effect on crop growth for a season unless balanced with a high nitrogen source. Far better to use it on paths and then use it as a soil improver when it has rotted. In effect the paths become a sheet composter.

Posted in Allotment Garden Diary
6 comments on “Using Woodchips in Allotment & Garden
  1. Julie Peel says:

    Thanks for this. I also use no-dig and have access to a lot of woodchips so use them on my paths. My soil is sandy loam and pretty acid so overly free drainage is more of a problem, unlike clay. I was very interested in the idea that the chips actively suppress weeds on paths owing to nitrogen depletion. I do still get some annuals as well as a lot of couch and bindweed coming through the woodchips and all the tap rooted weeds, but this is my first year on the allotment so I’ll see what happens next year.

    As a matter of interest, do you think it’s worth trying to compost the woodchips with chicken manure separately from my other compost bins? No dig does need a LOT of compost. I have had to buy most of it in this year (as my first) and am not sure I will generate enough of my own to fulfil what I’ll need next year, so this could be a cheaper source if it might work?

    • John Harrison says:

      Hi Julie – You could build a pile of woodchips + chicken manure and just leave them. I did similar with woodchips and sulphate of ammonia and it took 2 years to become a usable soil conditioner if not a good compost.
      Incidentally, I’d fork the soil to open it (just rock the fork rather than turning the soil) in the winter and then lime it if I was you. The acidity makes a larger difference than most imagine to plant ability to utilise nutrients.

  2. Keith Singleton says:

    We make a product using bark that has been granulated and composted mixed with composted manure and seaweed (properly composted wood chip mixed with a little sulphate of ammonia works as well in addition or in lieu of the bark) This can be used as a nutritious mulch or dug into the soil. Worms then work 24/7 to mix this into the soil in the process aerating heavy clay soils and improving the water holding capacity of poor or sandy soils. It works great as a planting compost when added to the soil taken out of the planting holes and greatly assists in preventing stress to the newly planted shrub or tree. It is called Just Naturally and Just Naturally Plus which is further enriched with Fish Blood and Bone.

  3. Julie Peel says:

    Thanks both for that. I’ll give it a go and also add lime this autumn. Nothing to lose even if it does take a couple of years to rot down.

  4. Steven Dean Stillwell says:

    Having read this article on fresh wood chips now has me wondering about the wisdom behind a raised bed idea using logs. The logs were not only used as the edging (risers) of the bed, but also were to be added to the base of the raised bed. There was a dig and save of the topsoil layer, then another foot was dug out and saved separately. After the soils were removed from the bed foot print a layer of logs was placed in the bottom of the foot print, then the extra foot of soil dug out and reserved was put back in the footprint of the bed, finally topping with the reserved topsoil and first addition of compost.

    The argument in favor stated that the buried logs, as they decomposed, would assist in maintaining a constant level of moisture. It sounded plausible and I was going to try it in the next bed I convert to raised from a traditional bed. Would be interested in your thoughts now that I have read your information about wood chips – fresh wood in particular.

    • John Harrison says:

      Sounds like you’re talking about Hügelkultur which I’ve no experience of. Could be worth doing a bed and seeing how it does compared with a more conventional bed if you’re in a fairly dry area.

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