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When to plant Petunia

Computed from land-grant Extension planting-window rules (cited below), localized to real ZIP-level median frost dates, not a single national guess. These are national-generic rules by hardiness class; individual state Extension offices layer their own regional adjustment on top (earlier in the Deep South, later in the Upper Midwest). Enter your ZIP for your own dates, or read the four representative locations below.

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Representative timing, by climate band

When to plant Petunia in four US climates

Each column is the most nursery-dense location in our directory within that USDA zone band, computed from that location's own real median frost dates, not a made-up example.

Zones 10-13 (hot, frost rare or absent) (Loxahatchee, FL): Frost is rare here (about 359 frost-free days a year); most years see little or no hard freeze. This is a semi hardy crop. In climates like this one, hardy and semi-hardy crops typically go in during the cooler months (fall through late winter), not on a frost-relative schedule.

Petunia's hardiness rating depends on which extension office you ask. University of Illinois Extension lists it as a half-hardy example, alongside ageratum, geranium, dianthus, lobelia, and gazania, plantable about two weeks before the frost-free date. Clemson Cooperative Extension's Growing Annuals factsheet and its dedicated Petunia factsheet both instead call it tender, instructing growers to plant "as soon as the danger of frost is past."

This page follows the Illinois convention and classifies petunia semi-hardy, widening the transplant window to two weeks before through the frost date itself so it brackets both recommendations rather than picking one and discarding the other.

Start seed indoors eight to ten weeks before planting, per Clemson's dedicated Petunia factsheet; no extension source gives a first-bloom day count. Petunia is sold at the nursery mainly as started flats and hanging baskets rather than seed, since that long indoor lead time makes seed-starting impractical for most home growers.

Sourcing notes

DISAGREEMENT: University of Illinois Extension's Annuals page explicitly lists petunia as a half-hardy annual example (with ageratum, geranium, dianthus, lobelia, gazania), plantable "about two weeks before the frost-free date." Clemson's Growing Annuals factsheet and its dedicated Petunia factsheet both instead classify petunia as tender, instructing growers to "plant petunias as soon as the danger of frost is past." Classified semi_hardy here per the Illinois convention, with the transplant window widened to -2 to 0 weeks relative to last frost to bracket both recommendations. Indoor sowing (8-10 weeks before planting) is sourced directly from Clemson's dedicated Petunia factsheet; no extension source gave a first-bloom day count.

Sources

• Clemson Cooperative Extension Home & Garden Information Center, Growing Annuals (HGIC 1152) (accessed 2026-08-04)
• Clemson Cooperative Extension Home & Garden Information Center, Petunia (accessed 2026-08-04)
• University of Illinois Extension, Annuals (Flowers) (accessed 2026-08-04)