S is for Sustainability this Earth Day. Yesterday I introduced Tom Benjamin who designs sustainable, low maintenace landscapes to an attentive audience at our local 'Little e' (not the Big Eastern Exposition in Springfield) where the theme was saving energy.  The topic was Reduce Your Lawn and Increase Your Leisure. Since I have been writing about low-mow landscapes I was interested to hear how Tom calculated the benefits. There are many. The first benefit, according to my husband, is…