WARNING: i don't want to harsh anyones mellow but this crap gets my panties in a bunch so don't read on if you want to "believe" in moon planting...
i thought this sounded like pseudo-science and sure enough - it unfortunately is a bunch of hooey. Yes the moon is the cause of ocean tides. Yes, when the moon and sun are in a line, gravitational forces are stronger which causes high tides. And conversely, when the sun and moon are opposite the force isn't as strong and you get low tide.
BUT the tidal effect occurs because the ocean is so large (has a lot of mass) and the moon is far enough away to have gravitational force of its own that isn't counteracted by the Earth. But the moon planters are saying that underground water droplets are effected the same way. But the idea that gravitational force is equal for things with different mass (ocean vs. droplets underground), at that distance, is refuted by any physics book (I think it is Newton's inverse square law). In a nutshell, the greater the mass the greater the gravitational effect (both causing and caused) over distance.
in other words, if the site you pointed to was accurately describing gravitational pull, then the water in your drinking glass would be "higher" at full moon. and all the bottles and cans in your fridge would burst because of this gravitational pull. That would happen if the theory the moon-planters are suggesting is true. But that doesn't happen, does it? Or maybe a better refutation of this idea is we'd all weigh less thanks to the moon's tugging on us every full moon (which is every 30 days). again, that doesn't happen.
I have read the Farmer's Almanac. You'll find a lot of myths, fairy tales, old-wives tales, etc.. in it. The Almanac certainly isn't science nor is it accurate. The moon did have an effect on some farmers however - the full moon allowed them to continue harvesting later into the evening thanks to the extra light known as the "harvest moon".
I won't get into the astrology baloney that is also present on the lunar-planting site but if you'd like me to take the air out of that load-of-crap's tires, let me know.
here is another moon planting site:
Moon Planting
this one really cracks me up - if you go to their "facts" page, it actually says there is no evidence for most of what they are proposing and yet that doesn't seem to slow down their advocacy of moon planting... oh well.
oh wait -- it does say that Gravitropism is how plants know which way to grow - but Gravitropism is an EARTH-related phenomena -- nothing to do with the moon.
Sorry if this is harsh, but pseudo-science is very bothersome to me. I realize science does not have all the answers and it makes mistakes. But, at least science admits making mistakes. Something the pseudo-scientists rarely, if ever, do.
Ultimately, if you want to believe something to be true without evidence (or even in the face of evidence) that is up to you but not all of us like to put blinders on.