Zinnias are best started directly outdoors in locations where spring warms up early. Keep in mind that Zinnias are native to Mexico, where they have become accustomed to long, hot summers. They are classed as tender annuals and can be directly sown into the garden after all danger of frost is over and daytime temps are at least 50F and above. In cooler climates, start seeds indoors 4 to 6 weeks before your area’s average last-frost date. Harden off the plants by vacationing trays outside for a few hours per day before planting them in your garden.
