Hi from Hazel,
Cardboard over nettle roots was fine for me initially. A few popped through but easily dealt with.
An idea for the spuds is to put down a layer of compost, then cardboard, then punch a hole in the cardboard for each potato(easier when thoroughly wet), then cover with more compost. You can earth up each plant separately with more compost as necessary. The cardboard will be very delicate by the time the spuds are ready.
Sure there will be more ideas you can pick from😀
Good luck and fine weather!