Fertiliser isn't cheap - neither is organic fertiliser. I'm also a cheap skate and seeing as during the growing season you need heaps of fertiliser for fabulous veg, here's a guide to making your own.
For this instructable you only need:
Container - preferably with a lid
A thwacking stick.
Step 1: Collecting Nettles
Good stout gloves are a must, however you may also need a long sleeved jumper or thick long sleeved t-shirt to get a proper harvest.
Harvesting is simple - just pull up plant. Leave the roots if you can, but you ought to be able to snap off the stems without too much effort. You'll need enought to fill your container - don't be afraid to compact it down either.