With http://www.nexusmods.com/newvegas/mods/60320, you can use water to grow plants and trees throughout the wasteland.

Experienced survivalists can restore more than 7,248 specimens thought dead to life.

Plants will no longer regrow in the harsh desert without your aid.

Grow and Restore Plants
[Survival of 40 or greater required.]

Restore Trees
[Survival of 70 or greater required.]

Purified Water, Dirty Water, and Irradiated Water
[Grows plants and trees in 1, 2, and 3 days.]