[Kajazy]

Hello,

I'm setting up a new raised bed on some ground which has always been over-run with weeds. I've attempted to tackle them in all the usual ways, but to make sure (and look, we're talking horsetail, docks, thistles, nettles and bindweed - I'm just waiting to find Japanses Knotweed one of these days...!!!) I was thinking of builiding it on a base of cardboard, then filling the soil on top...
Good idea?
Bad idea?
What do you think...?

[mumofstig]

In my experience the weeds will always find a way through.
I would rather make the effort and remove the big rooted weeds first.

[DD.]

Agree with mum.

The cardboard will get damp and for those weeds it'll just like fighting your way out of  wet paper bag.

[sunshineband]

and in my experience those weeds have big tough pointy roots just waiting to force their way through anything in their way.

Dig 'em out first and save years of trouble

[Kajazy]

Ok - will give it another go, although the horsetail seems to come back no matter what I do (and I have to admit to the odd blast with chemicals on this persistent beggar...!), and hopefully this year they might not be as bad as last!

[Yorkie]

Marestail is a prehistoric organism.  It has silica coating on its leaves which is why for any weedkiller to be effective, you need to bruise the leaves first.

Best advice with it is from Aunt Sally, who says "Never let it see a Sunday".  If you keep it small then it will gradually weaken.

[compostqueen]

I lined my raised bed with cardboard years ago and it's been fine.  It was placed over cut down weeds. It was a fresh piece of cardboard from the electric shop and I put plenty down so there were no gaps.  Soil, compost, sand etc all in on top and it's been ok.  It is a deep raised bed though so maybe that's the reason for no weeds coming up through the cardboard

[Trillium]

My beds are deep as well, over 12", some more - depends on what I need them for.

I placed many cardboard layers down before I filled with soil, etc. but I made sure no dock, thistles or other big rooted ones were there. The couch died a quiet death  as did the grasses.

[bigben]

I would give it a good dig and try to remove all the roots you can before you try to build your bed.
 Cardboard and a load of soil will stop new seeds from germinating but some of the weeds you list can have big reserves in their root systems to power them up through a lot of soil. Bind weed has a tendency to just go sidewards and pop up at the edges of your bed. It is then even harder to dig out as the roots are not easy to get to.

Dig then see what pops up. You might need to resort to chemicals or as others suggest - persevere in keeping it down with hoeing.