If your small space has no green space, you might want to consider going very small and grow a garden in a bottle. Instructions after the jump...

1. Find a good sized bottle
2. Use it upright or turn it on its side.
3. Layer damp sand and small pebbles on the floor of the bottle. Consider a layer of activated charcoal to absorb any smells and a layer of moss to keep the soil from settling. Add your soil.
4. Choose seeds from small plants with similar requirements that can stand a good deal of humidity.
5. Place your mini-greenhouse in medium sun and tend it carefully.

[image via Medoria's Flickr Page, licensed with a Creative Commons License]