When to plant zinnia in zone 3b — planting calendar

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Showing USDA Zone 3B

Growing SeasonZone 3b

Last frost ~May 25First frost ~Sep 15Today

Start indoorsTransplant / sowHarvestFrost risk

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Start indoors Apr 27 · Sow May 25 · First harvest Jul 14 · Wrap by Sep 8

Last spring frostMay 25

Start seeds indoorsApr 27

Direct sowMay 25

First harvestJul 14

Last harvestSep 8

First fall frostSep 15

Why these dates work in zone 3b

Zone 3b's last spring frost averages May 25 and first fall frost Sep 15 — about 113 frost-free days. Zinnia is frost-sensitive, so the around last frost timing builds in a safety margin against a late cold snap — setting plants out too early risks losing them to frost. Starting seeds indoors 4 weeks ahead gives strong transplants ready the moment the soil warms.

Common questions

How long does zinnia take to grow in zone 3b?

Zinnia matures in about 50–70 days from sowing. In zone 3b that means sowing around May 25 and first picking around Jul 14.

Will zinnia survive frost in zone 3b?

No — zinnia is frost-sensitive. In zone 3b, wait until after the last frost (around May 25) to plant, and harvest before the first fall frost (around Sep 15).

For soil, spacing, pests and companion planting, see the full zinnia growing guide →