Sustainable gardening mimics nature as closely as possible. In the ecosystem, animals and plants thrive in symbiosis: animals eat plants and create valuable fertilizer for plants in return. Several low-maintenance animals keep well in a backyard and also produce nutrient-rich compost enhancements for gardens, even in urban areas.
Worms need little more than a box with drainage, bedding material such as torn newspaper or leaves, a handful of dirt for grit, and your kitchen garden scraps. In return for this scant attention, worms greatly speed up the composting process of organic materials by eating and digesting them. The resulting worm castings are ready to be added to the garden after a very brief stint in a compost pile.
Chickens, ducks, geese and turkeys all produce wonderful, rich garden nutrition in their manure. In fact, the all-important balance of nitrogen, phosphorus and potassium in poultry droppings is so good that studies have shown many vegetable crops to thrive with just poultry manure and no other fertilizer. Of all poultry, chickens are the most beneficial for the typical backyard garden. A few hens require little space, make far less noise than dogs, and produce eggs most of the year. Their feed is inexpensive and they love bugs, worms, slugs, weeds, and kitchen scraps, too. Add the manure to compost, and the rest of the pile will heat up even faster.
Rabbit manure is also fantastic garden nutrition, being especially high in nitrogen, and can go directly to the plants as soon as it is made because it doesn't "burn" them with too much acid. Rabbits make cuddly pets, and need little more than feed and a hutch to make them happy. Put a worm bin under the rabbit hutch and the worms will happily consume the droppings and wasted feed, adding to the compost in the process.
A few easy, low-maintenance animals close the loop on the remarkable relationship between flora and fauna, giving the garden a big boost in self-sufficiency and expense savings.