When to plant zinnia in zone 5b — planting calendar

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Showing USDA Zone 5B

Growing SeasonZone 5b

Last frost ~May 15First frost ~Sep 30Today

Start indoorsTransplant / sowHarvestFrost risk

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Start indoors Apr 17 · Sow May 15 · First harvest Jul 4 · Wrap by Sep 23

Last spring frostMay 15

Start seeds indoorsApr 17

Direct sowMay 15

First harvestJul 4

Last harvestSep 23

First fall frostSep 30

Why these dates work in zone 5b

Zone 5b's last spring frost averages May 15 and first fall frost Sep 30 — about 138 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 5b?

Zinnia matures in about 50–70 days from sowing. In zone 5b that means sowing around May 15 and first picking around Jul 4.

Will zinnia survive frost in zone 5b?

No — zinnia is frost-sensitive. In zone 5b, wait until after the last frost (around May 15) to plant, and harvest before the first fall frost (around Sep 30).

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