Zinnias can be started indoors about 4-6 weeks before the last expected frost in your locality. Use a seed starting tray or small pots with drainage holes filled with a quality organic seed starter mix that is pre-moistened.
Sow the seeds on pressing them onto the soil and lightly covering them with vermiculite.
Cover seed trays with a clear dome and move them under the grow lights on heat mats.
Remove the cover and heat mats when the seeds start to germinate. It’s OK if they didn’t all germinate, more will grow after the cover is removed.
Keep soil moist by bottom watering only.
Before transplanting zinnia seedlings outdoors, harden them off by gradually exposing them to outdoor conditions over a period of 14 days.
When seedlings are hardened off and ready to plant in the garden, space zinnia transplants about 9 inches apart after the last frost date.
Water young plants regularly, keeping the soil moist but not waterlogged. Feed with an organic fish fertilizer for a few weeks and then use a slow-release fertilizer so feeding them is set-and-forget.
Follow along to learn more about how to start seeds indoors.