I have been using cardboard this year and it is amazing!
We started off with the black landscape fabric but hadn’t found out about no dig at that stage so put it in as a base layer to prevent weeds growing into bed from underneath.DISASTER! Had to dig it all out again 6 months later. Also tried wood chip as weed suppressant to little effect as bind weed, nettles, thistles and dandelions all over and grew through thick layer of wood chip within weeks in summer. Since discovering Charles have started putting cardboard down and difference is amazing.
Under hedges I put cardboard with wood chip on top, nothing through at all.
We also had a weed ridden border which I put cardbaord 1st, then planted heather into holes cut in it, then put peat compost all over as mulch and it is doing well, heather alive and had to pull about 2 weeds in 2 months.
Where I plan to do beds next year I put some immature compost (pretty thin layer as I didn’t have much, hoped this would encourage worms etc ) followed by cardboard followed by the reused landscape fabric (mainly to hold cardboard in place). This seems to be going great. These beds were used this summer so weeds were mainly under control here I just didn’t want any work weeding over the next few months. No weeds and when I’ve peeked under all looks good.
Also had a new retaining wall put in due to building work so it is like a raised bed with a hedge at the back. I only managed to put cardboard on half as I ran out. The uncovered portion is now thick with chickweed/ and I can see other horrors getting established! Probably just needs a good hoe but it is all extra work which I find a bit demoralising as it is endless and will keep coming back. the cardboarded part looks pretty ugly but I know the work is all happening without me.
I think in your case the cardboard will all have decomposed by the time you are planting so will do no harm. My only thoughts are maybe put a little compost or leaf mould under it to encourage soil activity? If weeds are under control in general and you have a thick layer of compost you may not even need the cardboard ( but i’d be safe and stick it down!)
In fact the only trouble I find using the cardboard is getting hold of it. I have been discovered twice now, rummaging through recycling bins behind the local bike shop. Bit embarrassing!
