New raised vegetable bed - to cardboard or not to cardboard?

WildFlower_UK

I recently installed a new raised bed and the compost/manure/top soil mix arrived today.

Before I fill the new bed, I'm still unsure about whether I should add a layer of cardboard between the cleared ground and new soil mix. Images to follow but you will see there are still some roots in the ground soil from when we took up the turf.

Questions are:
1. Will these roots likely cause major issues if I don't remove them? Or will the layer of new soil effectively suffocate the roots?
2. If I add the cardboard layer over as it is, I presume it will take a fair few months to breakdown therefore affecting what I can grow in the space as the without access to the ground beneath the bed is quite shallow?

We have clay soil. While we were building the raised bed we had to walk over the cleared area, compacting it. We have turned over the top 2-3 inches of soil to loosen it up. The size of the bed is 2m (longer sides) by 1m (shorter sides) and the depth of a scaffold board, so around 10 inches. I plan to grow courgettes, dwarf French beans, some herbs, radishes and beetroot in the bed this year.

Not sure what's best, any help greatly received.

Bilje

Well if it was me and on the assumption you're filling the raised bed to the top I wouldn't bother putting cardboard in. Break up the existing soil a little more first then add your mix. I doubt if ordinary grass roots would grow through a layer 10 inches deep. The cardboard might inhibit drainage but it would certainly inhibit the natural incorporation of soil bacteria worms etc which you would want to encourage. Good luck with it all. 

WildFlower_UK

Thanks @Bilje - that's what I thought, but you hear horror stories about not being prudent enough to completely rid an area of roots that I worried they might fight back! I can break up the clumps more before filling. That's my evening sorted, then!

Obelixx

Cardboard is good for covering soil to which just a few inches of compost or mulch are to be added.  It does need to be soaked once in place and before mulching.   It will keep the light off any weed seeds lurking in the soil below and the worm sand other soil organisms won't mind it at all.

If you decide to keep your cardboard for later, just break up those clumps of soil with a fork rather than serious digging and remove any visible roots in case they're couch grass or bindweed or thistles.

WildFlower_UK

Thanks @Obelixx! We left off the cardboard in the end but did break up the clumps and remove the largest of the roots.