What I do is 3/4 fill a container with stinging nettles, not the roots. Cover with water and allow it to sit for 4-6 weeks. It will smell foul but is a great fertiliser for fruit flowers and veg. Don't apply it neat, it needs to be diluted, I'd add about a cupfull to 7ltrs of water.
You can also make some using Comfrey. Good luck.