Alnus incana subsp. rugosa (Speckled alder) is a native shrub of bogs so it does prefer slightly acidic soils that are wetter. The tree has early spring flowers that are interesting, but not really showy to the layperson. This plant spreads through rhizomes (roots) and can be used quite effectively in stream banks and floodplain plantings, where other species may be difficult to establish. However, be careful, it can be overly aggressive in small landscapes quickly forming thickets.
Frequently Asked Questions
Photo 1: By Quadell (inmygarden) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons