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I've been offered several deliveries of fresh wood chip from a local tree surgeon. This is ideal as we are planning on building new 'no dig' veg beds ready for use in the Spring (~5 months away).

I understand that wood chips, no matter what type, need to be left to rot for a few months before use, to avoid 'nitrogen robbing' and (in some cases) phytotoxin breakdown.

The plan is to use wood chips for the paths and 15cm of manure for the veg beds, all laid over a double-layer of cardboard (i.e. 'no dig' beds).

My question is, since we won't be planting any veg for a while yet, is it okay to prepare the paths and beds now, or do we still need to let the wood chip rot in a pile for a few months before putting down as paths? I'm not sure whether (a) effective rotting only occurs when in a large pile and/or (b) 'nitrogen robbing' would still affect the manure we would be setting the wood chip down alongside, even though we won't be planting anything into it just yet.

The reason for asking this (rather than waiting until Spring) is I have spare time now to make the beds, but will be much more busy in the Spring. If I can prepare the beds now, that would be a better use of time.

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There is absolutely no need to let wood chips sit before using them as a mulch. The "nitrogen-robbing" you refer to does happen, but it happens only at the soil-mulch interface and not below the soil surface, where the plant roots are. Here's some info to back up my statement. As the chips decay, the bacteria that "robbed" the N die, releasing it back into the soil. At that point, the cycle is self-repeating, so you won't need to add any amendments after that unless you feel the need to.

You especially have nothing to worry about since the chips are being used for paths. If it matters, I've been using chips for over 15 years now, in ornamental gardens, and have absolutely never had any issues. And my soil is great :)

I'm more concerned about your desire to use cardboard in your garden beds. This is actually a terrible idea - the science behind this is quite clear. First, here's some information from about 10 years ago for reference. The author is Linda Chalker-Scott, a professor emerita from Washington State University and a respected biologist.

Now, for more modern information. This is from a blog maintained by the horticulture professors at the same university. Here's the relevant post. To pull a little bit of this information into this answer, one of the biggest issues with cardboard is its ability to reduce oxygen movement into the soil, it also can cause issues with water and insects; this is noted in both references I've included. Be sure to read the comments section, as Dr. Chalker-Scott addresses Charles Dowding, a proponent of using cardboard, in her comments.

You can easily go no-dig without cardboard. Here's my method for my vegetable garden. This is anecdotal! But it has worked for decades for me (Zone 5, USA - min temp in winter is about -15F to -20F).

For plants (rather than direct seeding):

  1. If desired, fertilize the soil.
  2. Plant the crop - tomatoes, cucurbits, whatever.
  3. Water the new plants.
  4. Put down an organic mulch (note that I don't use wood chips in my vegetable garden). For a mulch, I use cocoa bean hulls because they're relatively inexpensive in my area. Other options would be rice hulls, weed-free straw, shredded leaves, shredded newspaper (ONLY use shredded paper!)

For direct-seeded plants like carrots, beets, etc., I don't mulch until the seeds are up and have put out their second set of leaves. I then mulch much heavier between the rows than up against the seedlings, using the same mulch as above.

So - that's all there is to it. I never turn my soil over. If you use compost, then you can work it into the soil a bit if you want when you apply it, but other than that you should never need to dig anything with this method.

Will you get weeds? Sure, a few, especially around the edges of the bed where the mulch may be a bit thin, but after a couple of years of building tilth through composting and mulching, the weeds are a breeze to pull out.

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  • What a detailed answer! Thanks! Oct 15 '20 at 17:38
  • Thanks Jurp. Note that these beds are for vegetables, and the first article you linked states "The research does show that there might be an issue with shallow rooted plants like annuals and vegetables so don’t use chips there". On the subject of cardboard, we are based in the UK where mulches on top of the soil such as straw tend to attract slugs. Dowding's cardboard method is intended to be completely buried, so many of the issues mentioned in the second article don't apply. I guess the method's applicability needs to be taken in regional context. Any thoughts on phytotoxin breakdown? Oct 15 '20 at 19:13
  • Your post said you were using the chips for paths, which is why I answered as I did; besides, the comments in that first article recommend using the chips as actual mulch in the vegetable garden. I don't use them because I would probably bury them over time, which DOES steal nitrogen from the soil. Also, they would tend to be a reservoir for septoria wilt, which is common where I live. As for Dowding's method, burying the cardboard will absolutely cause the same issues with impermeability and oxygen exchange with the soil beneath the cardboard; it may help break it down sooner, though.
    – Jurp
    Oct 15 '20 at 20:07
  • Oh yeah - phytotoxins... As far as wood chips go, there's nothing to worry about. From Dr. L-C (s3.wp.wsu.edu/uploads/sites/403/2015/03/toxic-yard-waste.pdf). You're more likely to get phytotoxicity from young compost. You could also get some toxicity from the cardboard, depending on if it was treated for permeability, the glues used to construct the original box from the cardboard, and what kind of inks were used on the printing, if any.
    – Jurp
    Oct 15 '20 at 20:11

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