Composting is a great environmentally conscious alternative to fertiliser. It’s also easy to do. Makes sure you have a suitable location where you can allow useful creatures like earthworms to get in, without encouraging vermin.
Start out with some soil and any worms you can find. Add grass-clippings and vegetable waste. Once it gets going, your compost heap will provide you with a fantastic source of natural fertiliser for your garden. Added benefit: it costs nothing!