What is the best single crop for small scale self sufficiency farming in temperate/subtropical regions?
I don’t think that you can be self sufficient on a small acre farm growing one crop. It is sort of going against the idea of being self sufficient on a farm. To be truly self sufficient you need to produce everything that you need on your acres of land. You will need a variety of crops to assure a proper diet, and as insurance against one crop failing. You will need an oil seed crop to produce fuel, some chickens for eggs and meat, a cow or goat for milk and cheese. You will need to produce feed for your animals as well as the manure of the animals for fertilizer. You will also need a small orchard for fruit and nuts. The following site should help you out. http://www.self-sufficient-farm-living.
