Use a hand lens and see if you can see any tiny insects, particularly on the undersides of the leaves. It looks like it might be spider mite, thrip or possibly aphid damage.
Perhaps the last pic is another but less well developed one, LB? I'm always torn between picking and eating the heads or letting them flower as they are beautiful and loved by insects.
This is my Globe Artichoke:
While magnolias prefer a slightly acid soil, they grow perfectly well in neutral soil and I would go with H-C's suggestion of a mix of garden soil and a loam-based ericaceous like a John Innes. It'll actually appreciate being in a bucket of water for that sort of length of time.
The first one is the Globe artichoke I think nut. I have one growing - will nip out and take a photo in a bit.
Plants do need a dark period for photosynthesis to work properly. Some info. here:
It's an F1 hybrid 'all female' type. However, these types can still produce male flowers (no 'mini cucumber' behind the flower) which should be removed otherwise pollination can occur resulting in a bitter fruit.
You don't really need to worry about it taking nitrogen when used as a surface mulch, Judith. If you wanted to mix it with the soil to improve the soil structure, that's when you could come across this problem.
The first one could be a few things. The second is pulmonaria by the look of it.
They really need to be planted into the garden and don't do very well in pots, Sue. You could try it in a very large one (50cm+) using a John Innes #3 compost or garden soil mixed with well rotted manure but it would need a lot of looking after (regular watering and feeding.)