SHORING UP ENERGY OF THE HOUSE

Planting a row of trees behind the house acts to shore up the energy and symbolically keeps it from flowing away. This translates into keeping the health and wealth where it belongs. It is also believed to be difficult to conceive sons in a home that has sloping land behind the house. So if it’s boys that you want, plant the row of trees.
Source: http://www.saintdeck.com/Articles/FengShuiofTrees.htm