Some grocery store potatoes may have been treated to inhibit sprouting to prolong shelf life, but since yours sprouted, that wasn't an issue. Also, store bought potatoes might not be certified disease free. Seed potatoes at a garden center are usually certified. Plus, you can usually find more variety of seed potatoes from a garden center or garden catalog, and some that might be more adapted to your climate, than those at a grocery store. However, lots of gardeners have success using grocery store potatoes as seed potatoes. In Tennessee, March is the ideal time to plant potatoes, but April is fine, too. The success of your potatoes will depend in part on what variety you have planted and when, based on your local climate. Potatoes like cool weather, can stand light frost, and don't do so well in the heat of summer. Check your frost dates. Nashville, for example, has a last spring frost around April 6 and a first fall frost around October 28. (See the frost calculator at: http://www.almanac.com/content/frost-chart-united-states). Early season potatoes mature within 75 to 90 days; midseason, about 95 to 110 days; late season, about 120-135 days (these store well usually). Potatoes grow best in cool weather, when soil temps are about 60 to 70F. It's best to get the crops harvested before the heat of summer, or time them to mature in fall. In areas with hot summers, early and midseason types grow well in spring plantings (plant about 3 to 4 weeks before last spring frost); late season types can be planted in early summer for a fall crop.