Freshish wood chips as filler for bottom of raised vege garden

Question

I have built a raised bed (about 60cm high) and want to fill it so I can start growing stuff. Unfortunately the cost of vege mix/garden mix is quite high - so I'm wanting to add something as a filler.

I have a considerable amount of wood chips which I managed to get for free when the neighbour cut down trees (wood chips has been sitting for a little over a month). I'm seriously considering filling the bottom half to 2 thirds of the bed with this mulch - but I'm very concerned about their absorption of nitrogen - and then covering it with vege mix for the top 1/3rd to half, and growing stuff.

The only thing I've been able to find online - which says its OK - is https://backyardgardengeek.com/bark-or-mulch-in-bottom-of-raised-beds/ - but I'm not convinced

Is it a mistake to do this, and are there common veges that are better/I should steer away from for the first year if I do proceed? (FYI, its spring here. I'm in the equivalent of US hardiness zone 9b I believe)

Answer 1

I think it would work OK, it would certainly drain well. You would be more or less making a Hügelkultur. This study found adding a layer of wood chips under the soil did not reduce Nitrogen availability, but they also had twice as much topsoil as you're intending, and used equal parts leaf mould and woodchips. I would try to get my hands on a load of fresh manure or something to mix in if I could. It would be a big improvement.

You will also want to think about what plants you will be planting there, and how deep their roots can reach. I think you want at least 30 cm of soil for the roots to go down into, and maybe much more. I'm not sure how well the wood chips would serve as a growth medium by themselves, but I've worked very large amounts of wood chips into the under-layer of garden beds I have double dug with great success. I hope your more severe version is successful too :-).