Often, seemingly conflicting sources may both be correct. For instance, growth rate in warmer, more southern areas may be much greater than in colder climates. Also, conditions in one part of a single hardiness zone area may be strikingly different than those at another, in another part of the country. Mature size may refer to different ages when discussed by different sources. There is no true standard for "mature size" data.

All that said, I find the Missouri Botanical Garden's Plant Finder site pretty useful and generally accurate. www.missouribotanicalgarden.org

I almost never use only one site. I try to get a consensus view from three or more sources.

Thanks!