Comfrey: The Comforting Herb

Comfrey is great for churning soil. If you have useless soil, plant some comfrey and you'll have good soil in no time. It is very hard to get rid of once you decide to plant other crops as even the smallest piece of root left in the ground will propogate, however, it is probably a great companion plant regardless, and you can use the leaves and root to make a good insecticide by steeping in a bucket of water for a week and then spraying on plants. Add garlic to the steeping solution as well.