I have soaked a bucket full of nettles but can't remember how long to leave it for and which plants to use it on?
It will turn brown in about two weeks.. You will probably know by the smell, although nettle stew is not as bad as comfrey. Pour off/strain the liquid. Dilute so that it looks like weak tea. About 1 part nettle stew to 19 parts water. ( 500ml in a watering can full) is a good tonic for leafy plants like cabbages that need a lot of nitrogen. You can use it all brassicas, cabbage, kale, etc.
Comfrey is higher in potash and is better on flowering plants like tomatoes, potatoes, courgettes etc.