Viola seeds can be sown directly into the garden, though most growers will use seed starting trays in order to improve the germination rate and more closely monitor temperature. If sowing outdoors, sow them in the late fall or early winter for spring blossoms or as soon as the soil can be worked for early summer blossoms. Viola seed needs darkness to sprout, so cover with 1/8 to 1/4-inch soil and ensure the bed stays moist, not wet. Viola seeds require cool soil temperatures, below 70°F for germination. If sowing indoors, your room temperature between 70 and 75°F will be fine, the growing medium normally being cooler than the ambient air temperature. If using egg or yogurt cartons, put them on a cookie sheet, wrap in plastic and then cover with damp newspaper, checking daily to ensure they stay moist, not wet. Once they sprout, move them to a sunny window and eventually outdoors, acclimating them to both day and nighttime temperatures before planting outdoors permanently. Germination normally takes 8 to 15 days at soil temperatures between 65 to 70°F.