Here's a nice recipe that I just tried for the first time and thought I would share with y'all.
Here are the ingredients:
Three banana peels, with the woody stems cut off.
Three days' worth of used coffee grounds. No need to be picky; a little mold is fine.
A few cups of water. I used tap water, but mud-puddle water would do just as well.
Blend in the blender until well liquefied. Voila! Doesn't it look great?
Okay, now take this delicious concoction and share it with...
...your plants! You didn't think I expected you to drink it, did you? Please tell me you haven't tried it yet.
Why it works: the banana peels are loaded with potassium, just as the bananas inside them are. Rosebushes and tomatoes (I have both) like a little extra potassium. And the coffee grounds are a treat for the worms, who supposedly love them. Worms are good for your soil (they aerate it, and their castings are very fertile) so it's not a bad idea to keep them happy. :)
Of course, you don't actually have to make a smoothie out of these ingredients; you can "plant" banana peels beneath your tomatoes or rosebushes, or just toss them on the ground around the plants. But my planting is done already, and I was afraid that banana peels lying around would be too smelly and attractive to varmints. So I chose this slightly more labor-intensive method.
Coffee grounds are also good for lawns, so if you don't have a garden, you can still put those grounds to use (or save them for me!)