I tried to post this the other night and the dang board wasn’t accepting anything - but, as has been implied - there are a couple of limiting factors that make the question ludicrously meaningless. #1 - just one 10 ton tree is made up of 10 tons of water and CO2. How ya gonna get those supplies up there? #2 - And supposing you found a way to plant hundreds of thousands of trees, and grow them, and extract the oxygen and release it onto the surface of the moon, there is not enough gravity on the moon to retain the oxygen, so it would dissipate into space. So - the suggestion here is to not try that for your next science fair project. It wont work.
Not to mention the fact that the lack of gravity would tear our plants to shreds.
There may be water on the moon see this
http://stacks.msnbc.com/news/192179.asp?cp1=1
But as everyone pointed out it won’t do much good.
The only thing I know growing is old.
How about Mustard plants on Mars instead?
As 647 said, it’s because GW Bush won’t do it. He’s to blame for the next four years.
If Bush could just get rid of the 50% chance of rain for Saturday; maybe ship it to the moon to water the trees.