Wait for warmth and passed frost danger
No single spring date fits every garden
Zinnias cannot survive frost. Use your local frost pattern and soil conditions instead of copying a national calendar date.
Match the method to the goal
Direct sowing is simple and works well in a warm bed. An indoor start can bring flowers forward. UMN lists zinnia starts at about three to four weeks before outdoor planting, while Illinois describes starting indoors several weeks before the last frost for a head start.
Plant for air flow
UMN plants direct-seeded zinnia at one-quarter inch deep and gives an 8- to 24-inch spacing range by plant habit. Oregon State recommends thinning seedlings to improve air flow, which helps limit powdery mildew later in summer.
Keep the first plan simple
For direct sowing, prepare a sunny, well-drained bed and wait for warm soil. For an indoor start, choose a short lead time and avoid putting seedlings outdoors before frost risk has passed. Read the packet for the selected variety's height and spacing.