The Telegraph in London depicts extreme gardening which for them is using the rain forest tree upper structure for a green house. Although it may be difficult, my form of extreme gardening is done in the remnants of Lake Passaic which is the remnants of the last Ice Age as it moved south to the north central part of New Jersey. I have to deal with the remnants of boulders pushed down by massive glaciers which stopped just north of Princeton by some thirty miles, having managed to leave in its wake the massive Lake Passaic, and the droppings of some two to three thousand miles of rocks.
Thus each time I seek to plant one of my seedling I get the chance to discover another rock, of on the average 30-50 kilos! Thus I do not use shovels but I use large steel bars, Johnson Bars, to dig holes, through compacted clay, and each time hitting a reminder of the glaciers.
Extreme gardening, tree tops, no rocks, well hardly, that is for wimps! Try New Jersey soil, Garden State, no way until you are below Princeton. Some how we American gardeners face challenges that are unknown to many.