You can make nettle or comfrey fertilizer (often referred to as "tea") by roughly chopping the leaves and stems stuff them into an old onion sack, with 1/2 brick in the bottom, tie the top with a length of rope immerse into a rain butt (like a giant tea bag) and you should have a liquid feed in about 3 weeks.
It'l pong like heck but hey....its free.