How many volumes in dvd are there in tv anime "law of ueki"?

Answer 1

So far seven volumes have been released with an eighth to be released in July.

But we can calculate: There are 51 episodes. The English DVDs are being released with 4 episodes per DVD. 12 DVDs would contain up to episode #48, so the 13th would contain only three episodes (#49, #50, #51).

AnimeOnDVD.com indicates that there will be 13 volumes as well. Their releases page:
http://www.animeondvd.com/releases/releases_by_date.php
... says that the next release is "Law of Ueki Vol. #08 (of 13)"