Could be the roots were congested and can't take advantage of the water you give them. Did you soak the plant well before you planted it?
Buy yourself some cheap stuff from Wilko and wrap it around the tank.
Stop doing whatever you think people will look in to see! Save your money.
Earwigs are not too great a problem. Catch them in flowerpots stuffed with straw inverted on sticks among the dahlias.
My anemones are now in their fourth year. They have finished flowering for this year but I'm sure they will flower again next year.
They are not really ready to be harvested until the foliage has dried up, but you can take onions for the kitchen as and when you need them. Let the foliage keel over naturally - don't help it!
The very best way is to dig out the roots. No weed killer required. Weak growth will come from some of the roots left behind, but easily disposed of. The dug out roots will burn well. Good luck.
Do not cover the foliage. Just pile up the soil to cover the lower stems and the potatoes to prevent the light getting at them.
They are edible if you need the space.
Donate it to a park. anonymously if necessary.