Trees Funny you say that you use yours as a retaining wall. I recently saw your near exact principle employed towards a house on Foxtel's, Grand Designs, one of those houses built 'into' the ground. Crop rotation is a great way to replenish soils. I remember this from Social Studies at school. One year one has nothing planted to give it a 'rest'. I also read somewhere to plant a legumes crop and dig it back into the soil to fixate nitrogen. And you can't do it in suburbia, but burn a crop 'back into the soil'. Obviously these days there are environmental issues with doing this. Still, these measures could save you a fortune from using synthetic addatives to replenish.
