April is National Gardening Month and a good time plant a garden, said University of Missouri Extension horticulturist David Trinklein. For those who lacked the motivation in the past to garden, consider the following benefits of this popular pastime.   • Economic: Vegetable gardening is an excellent way to save on the family food bill. The National Gardening Association (NGA) estimates that a well-maintained vegetable garden yields an average return of $500 per year. Multiplied by the number of vegetable gardens in the country (36 million), the NGA estimates that American food gardeners produce more than $21.6 billion of vegetables annually. Trinklein adds that you don’t have to spend hundreds on a raised bed filled with an artificial growing medium to benefit economically from gardening. A recent study by Burpee Seed Co. revealed that $50 spent on gardening supplies can be converted into $1,250 worth of produce annually. This twentyfold return on investment also was documented by…