When woodchips aren't working

I've built some new raised beds this year; 6 beds, each 10ftx4ft, each 1ft tall. They are on an area that has historically been grass, reeds, docks, creeping buttercup and alike, but it's the only flat, sunny part of our landscape. It's also very compacted, stony (really stony) soil, and gets very wet in the winter. I thought I would look to improve the soil, in order that in future years it has not only less compaction but also more life, so it can cope better when it's wet. The wet is also why I've made the beds a full 1ft tall.

I didn't have enough to cover the whole area, but I covered all the paths in cardboard and 6"+ of woodchips. In less than a month, the buttercup and plantain have already busted through in some spots.

I appreciate some will say I should have added more card (double cardboard in most of the space) and that I simply didn't add enough material (6" seems like it should have been plenty) but I am where I am now and wonder if anyone else has faced a similar challenge? What did you do if so? It's pretty impractical not to mention super expensive to add more woodchips (I'm in the UK, and free woodchips do not exist in my area). Massive labour in digging everything up again, I'm at a loss.

Any help appreciated.

I have a pretty similar situation. Two things: I've found that weeding those deep roots out of the wood chips is much easier than out of soil, so that's nice even if it's not proof against weeds. And I'm also adding another six inches of chips. The beds will be a bit sunken-feeling instead of raised, but whatever works!

From my experience, I have found that there is a critical mass that has to be achieved to get a good smothering effect from wood chips.

As you might of experienced with time, woodchips settle out and your initial layer goes from lets say 6" down to 2". I've done back of the hand experiments with a cardboard smother layer + 12" of chips, a kraft paper smother layer and 12" of chips, and a bed of just 5" of woodchip.

Both 12" woodchip layers have done remarkable with eliminating grass and weeds. No difference if it was thick corrugated board or just a layer of paper. The 5" bed has areas of grass/weeds poking through. It also didn't start until the chips settled with the rain down to a 2"ish layer.

Let me try to spitball some ideas that might help you seeing as getting more woodchips would prove difficult for you.

I too have wood chip pathways between my raised garden beds that I top off yearly. However it isn't always woodchips. It isn't the right season at the moment, but fall leaves work wonderfully. They might get a little slippery in rain but I tend to rake them in slightly with the chip so I don't have a slick walkway. I also have been known to rake back areas and spot add some kind of smother layer and recover if there seems to be an area that might be growing weeds. I'm not talking going DEEP, just enough to bury the smother lay.

Do you happen to have pictures to better visualize the space and where the weeds are popping up?

Christopher Weeks wrote:I have a pretty similar situation. Two things: I've found that weeding those deep roots out of the wood chips is much easier than out of soil, so that's nice even if it's not proof against weeds. And I'm also adding another six inches of chips. The beds will be a bit sunken-feeling instead of raised, but whatever works!

Thanks, yes - raising the whole area, as opposed to just the beds. It's just hugely expensive - it will cost at least £250-400 for enough chips to cover everything with another six inches.

Timothy Norton wrote:From my experience, I have found that there is a critical mass that has to be achieved to get a good smothering effect from wood chips.

As you might of experienced with time, woodchips settle out and your initial layer goes from lets say 6" down to 2". I've done back of the hand experiments with a cardboard smother layer + 12" of chips, a kraft paper smother layer and 12" of chips, and a bed of just 5" of woodchip.

Both 12" woodchip layers have done remarkable with eliminating grass and weeds. No difference if it was thick corrugated board or just a layer of paper. The 5" bed has areas of grass/weeds poking through. It also didn't start until the chips settled with the rain down to a 2"ish layer.

Let me try to spitball some ideas that might help you seeing as getting more woodchips would prove difficult for you.

I too have wood chip pathways between my raised garden beds that I top off yearly. However it isn't always woodchips. It isn't the right season at the moment, but fall leaves work wonderfully. They might get a little slippery in rain but I tend to rake them in slightly with the chip so I don't have a slick walkway. I also have been known to rake back areas and spot add some kind of smother layer and recover if there seems to be an area that might be growing weeds. I'm not talking going DEEP, just enough to bury the smother lay.

Do you happen to have pictures to better visualize the space and where the weeds are popping up?

Thanks, yes attached here; apologies, I thought I had attached to the original post. 12" sounds superb, albeit that it would be the same height as the raised beds initially! Do you think adding another 6", though, would be enough, or now that some weeds have already made their way through, that they will, effectively, only be under the top 6"?

Mj Lacey wrote:Thanks, yes - raising the whole area, as opposed to just the beds. It's just hugely expensive - it will cost at least £250-400 for enough chips to cover everything with another six inches.

Wow! I pay a local arborist $50 (or occasionally nothing) to dump a trailer (~six cubic yards) at my place, but I have to wait until he's working in the area and would rather dump them here than take them to the local pulp mill.

I can't say for sure if just putting another 6 inches on top would work, but I'd be willing to bet if you spot weeded and then put another layer on top you should be a lot better off. Might be worth just scuffle hoeing at the minimum before building up the layer.

I have a lot of fungus (intentionally) in my pathways so mulch gets chewed up pretty quick. I noticed this year I have a few dandelions and could use another layer of material but with the soil being so soft underneath, the weeds just pop out fine.

I feel your pain, MJ

I've had similar outcomes with cardboard and woodchips here in the mountains of Virginia, so a roughly similar climate. I have a big advantage in having free unlimited woodchips, so my response has been to keep laying it on thick, mixing grass clippings and leaves into the woodchips. This makes a pretty hot sheet compost that definitely blocks and/or kills off the underlying crabgrass, etc.

I think your case could still be workable, with a bit more labor to compensate for expensive woodchips.

Here's how:

My observations have been that cardboard or newspaper, layed down thick with plenty of overlap and no gaps, will very effectively block weed growth. But it is also the perfect food for earthworms and other bugs. Worms eat cardboard, make holes, plants grow through the holes. So it is only effective for a few months in the winter, and as little as a week or two in warm wet weather.

Solution:

Dig it all up every few weeks!

I know that sounds like a lot of work, but the mulch and cardboard will soften the hard soil, the worms have aerated the top layers, and left behind castings for your benefit. So scrape back the existing woodchip mulch and cardboard remnants in layers. Set aside the woodchips from the top layer, and add the decayed cardboard, worms castings and newly created loam layer into your raised beds. Dig out the more persistent weeds and grasses as they are struggling to make it through the mulch. Have no pity on them, root them out with a fork. Find a source of free paper/cardboard, lay it down to replace the previously consumed layer, replace the wood chips on top, and mix in any leaves, grass clippings etc to bulk up your mulch thickness and replace what has decayed. You can do it small sections so it is not too overwhelming, the woodchips removed from one area go back on top of the newly prepared previous area so you don't have to move the bulky mulch twice.

You've now got stacking functions in your mulched pathways:
1; weed-free non-muddy walkways between beds,
2; a continuous source of worm casting and top quality compost to feed your beds. Each time you get down to the the bottom layer, take out a few of the stones as they are exposed, much easier to work them out when the ground is moist and pre-loosened by the earthworms. I'm saving my rocks for future construction projects.
3; free rocks!
4; great aerobic exercise

Use a fork and/or wide-tined rake to minimize worm death.
When you see the first weeds/grasses peeking through the mulch, it's time to re-lay the cardboard and go to war on the crabgrass (substitute your local flavor of weed nemesis).
Keep an eye out for bagged leaves in the fall. They are your best free mulch.

I hope you find this useful,

bon chance!

Oh creeping buttercups!!! My bane too. Is your soil slightly acid? They do like that - compacted damp acid soil.....I didn't find an answer and just tend to live with them and chop/drop now.
I found that they crept through the gaps in the cardboard even with a big overlap, the only thing that really seems to stump them is a thick layer of newspaper, and even then they soon creep on top again.
Hopefully they are knocked back enough that some spot weeding will prevent them spreading again (if you don't want to embrace a buttercup path that inevitably will spread into your beds!) I have found that in my tree field mowing the paths has really knocked back the buttercup there, so you may find that just hoeing them off a few times will eventually work.
Personally I'd leave the plantain. They don't spread much, so make a reasonable ground cover in my opinion. I do like a messy look though :)