Compost is the gardener's black gold. Well-rotted manure is an excellent additive, and vegetables grown in it will not make anyone sick. Always wash any produce before eating, and wash hands after working in the garden. Well-rotted manure smells like humus or rich dirt. If the manure is too fresh, it will be full of viable weed seeds and smell like ammonia. The weed seeds will sprout in your garden. Your vegetable plants will grow very tall because they are getting lots of nitrogen; they may produce more leaves than vegetables. Put down about 2 to 4 inches of well-rotted manure per season.