The best time to plant zinnia seeds depends on your method and local climate:
- For indoor or greenhouse planting, start seeds in late spring (April or May), about 4-6 weeks before your area's last frost date.
- For direct sowing outdoors, plant a couple of weeks after the last frost date, when daytime temperatures are around 70°F. This is often in late spring, around May to early June, depending on your zone.
- If planting seedlings outdoors, wait until late spring or early summer once the soil has warmed to about 70°F.
- You can also succession plant every few weeks from spring through mid-summer to prolong blooming.
Zinnias are warm-weather plants and sensitive to frost. Avoid planting too early when soil or nights are still cold. They typically grow well in USDA zones 2-11 and flower about 60-70 days after planting. In summary, late April to early June is generally the prime time to plant zinnia seeds, either indoors starting in late April or directly outdoors after frost risk has passed around May or June.
