The best time to plant zinnias is after the last frost date in your area when the soil and air temperatures have warmed to around 70°F. Zinnia seeds can be directly sown outdoors once the danger of frost is past and the soil is warm, or you can start seeds indoors 4 to 6 weeks before the last frost date to get an earlier start. Zinnias prefer warm conditions and don't do well in cold soil or frost, so waiting until the soil reaches about 70°F ensures better germination and stronger seedlings. Direct sowing in warm soil often produces healthier plants without transplant shock. For indoor starts, use a heat mat and plenty of light to keep seedlings sturdy. If you start indoors, plant your seedlings outside after the last frost and soil warming. If sowing directly outdoors, you can plant anytime from the last frost until mid-summer to get blooms through the growing season. In summary:

• Start indoors 4-6 weeks before last frost date.
• Direct sow outdoors after frost has passed and soil reaches about 70°F.
• Plant seeds about ¼ inch deep and space plants according to variety needs (6-18 inches apart).
• Planting timing aims for about 90 days before the first autumn frost to ensure maturity and flowering.

This approach maximizes zinnia bloom production and plant health.