When Should You Plant Petunias?

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GardenSays

Sow petunias outside May 5 – May 12 — after frost danger passes and soil has warmed to ~60°F.

Sow from: May 5 – May 12
Last frost (typ.): May 5

Petunias are frost-tender and germinate poorly in cold, wet ground — unlike peas or lettuce, you wait until AFTER the last frost (May 5) and until the soil warms. Sowing too early into cold spring soil rots the seed. The safe window in Minneapolis, MN opens around May 5.

Do this this week

1.The main sowing window closed May 12

Calculated result · 3 verified sources · Checked 2026-07-18 · How we decide

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Why

Sow through the warm months; petunias stop producing once nights turn cold.

Warm-season crops need warm soil to germinate: cold, wet spring ground causes seed rot and poor stands, which is why they go in after frost, not before.
Days-to-maturity versus your frost-free season sets how late you can keep sowing.

When this doesn't apply

Transplant once soil warms to about 60F and frost danger has passed. Blooms from spring until frost.
A cold snap after sowing can still kill seedlings — hold off if a late frost is forecast, even inside the window.

How this was calculated

1. Last spring frostMay 5Source guidance
Minneapolis, MN: typical (50% probability) last 32°F frost
2. First sowing windowMay 5 – May 12Calculated result
Petunia is frost-tender — sow only after frost danger passes AND soil has warmed to ~60°F (0-7 days after the last frost)

Data sources

University of Minnesota Extension — Growing petunias — Wait until soil warms to about 60F and frost danger has passed before transplanting petunias. Space grandifloras and multifloras about 12 inches apart in full sun, closer in shadier spots. Need at least 5-6 hours of sun. (checked 2026-07-18)
NOAA NCEI — 1991-2020 U.S. Climate Normals (freeze date probabilities) (checked 2026-07-15)
National Gardening Association — frost date lookup (checked 2026-07-15)

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