Kansas planting calendar

When to plant onions in Kansas — sow, transplant & harvest dates

Kansas is mostly USDA zone 6b (range 5b-7a). Dates below are derived from onions's frost tolerance and Kansas's frost window — not generic national averages.

Onions planting timetable for Kansas

Stage	When in Kansas	Anchor
Start seeds indoors	early February (February 4)	10 weeks before the last frost (mid-April)
Transplant outside	mid-March (March 18)	28 days before the last frost (mid-April)
First harvest (estimate)	early July (July 6)	~110 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why Kansas's climate shifts the onions dates

Kansas's last spring frost averages mid-April and first fall frost late October, which sets the whole planting clock. Kansas has a long, hot, often windy continental season. Heat and drought stress matter as much as the winter low across the state. Sow early — onions bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Don't plant before mid-April — a hard freeze can still set young plants back. In the northwest High Plains (zone 5b) the safe date runs a week or two later.

Regional variation within Kansas

the northwest High Plains (zone 5b) runs roughly 1-2 weeks behind the state average; the south-central plains around Wichita (zone 7a) can plant 1-2 weeks earlier.

Wichita — USDA zone 7a
Kansas City — USDA zone 6b
Topeka — USDA zone 6b
Overland Park — USDA zone 6b

What else to plant in Kansas around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in Kansas?

In Kansas (mostly USDA zone 6b), sow onions indoors around early February, transplant outdoors mid-March (before the last frost, mid-April), and harvest from early July. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is Kansas?

Most of Kansas sits in USDA hardiness zone 6b, with the state spanning roughly 5b-7a from the northwest High Plains (zone 5b) to the south-central plains around Wichita (zone 7a). The last spring frost averages mid-April and the first fall frost late October.

Can you grow onions in Kansas?

Yes. Kansas's dominant zone 6b supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across Kansas?

the northwest High Plains (zone 5b) runs roughly 1-2 weeks behind the state average; the south-central plains around Wichita (zone 7a) can plant 1-2 weeks earlier.

What else can I plant in Kansas around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.