Usually, watering is not needed unless your soil is particularly dry or you're in the midst of a drought. If the area is small, a scythe will also work. This keeps weeds and annuals from choking out the vulnerable prairie plants. Keep a look out for weeds and pull them up, being sure not to upset any wildflower seedlings. Mow once in early June the second year and if all goes well you can start burning the third year, early spring.
Fire helps to burn away any excess fuels and adds nutrients to the soil.
Also, it allows for seeds to germinate that previously were prevented from doing so because of other plants shading them. Burning should be done every two or three years. Contact your local township or fire marshal for the appropriate permission. If burning is illegal or impractical for your area, mow your garden at least once a year in early spring or late fall. Your garden will require the most maintenance the first few months into the next few years.