Testing Old Seeds Seeds saved from past gardens may be worth sowing -- but only if they pass this test: Fold 10 seeds in moist paper towel, place in resealable bag, mark with date and type. Watch to see how many germinate. Multiply that number by 10 to calculate the percent of germinations. More than 70 percent is passing. If between 40 and 60 percent, sow thickly. Below 40 percent, it's best to buy fresh seed.