We bought a polytunnel! Yay, yay and yay! It's about 10'by 20' (3x6 meters).
The area where we will put it is covered with grass and weeds. I was wondering whether I could make the beds by putting cardboard on the ground and covering it with compost. Would the cardboard decompose as easily as it would outside? I suppose it would get wet because the plants obviously need water.
It should work more or less the same. I know a couple veggie farmers who use black plastic to solarize the grass to death inside a new tunnel. It might be a little late for that this year though. Although maybe not
Cardboard will certainly work under you growing area to suppress the weeds, but the area you walk around in? Maybe not so much. I tend to cover the whole area with woven weed fabric, then place raised beds around where I need them. Check out the pics. The heavy woven landscape fabric will last for years even in the walking area.
You can see what I mean in this post also https://planterspost.com/growing-tomatoes-in-pots/
No-Dig Vegetable growing techniques for the urban gardener