If you live in a high-density housing area with no room for gardens, then perhaps you could consider getting a community garden established. Normally it is a matter of finding some wasteland near your buildings that is council owned and not marked for development, then raising local support amongst other tower dwellers and getting names on a petition to show support. If you take this to council along with a proposal for a not-for-profit community garden and show you are prepared to do the work required yourself to get it established, many councils will contribute the land for this use.

If you think it is too much work, hold a public meeting, get some support and establish a committee to do the planning and organise supporters into working groups. After all, it's going to be shared public space, so you don't have to do it all yourself.

Here's a link to a site about starting a community garden if the idea interests you at all.