When to plant potatoes in zone 5b

Sow outdoors between Apr 17 and May 1. That is from 2 wk before to on the zone 5b's median last frost, May 11. Across most of zone 5b that date falls between Apr 7 and May 17.

Why a range: zone 5b is defined by winter lows, not frost dates. Its ZIP codes have median last frosts from Apr 21 to May 172, so a single zone date can be weeks off for you. The rule comes from Colorado State University Extension, written for CO and applied here to zone 5b's frost dates.

Last reviewed: 2026-11-02
Stations: 687
ZIP codes: 2,445

Photo: Pixabay / Pexels

These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.

Sow outdoorsColorado StateSow outdoors across most of the zone: Apr 7 to May 17Sow outdoors at the zone median: Apr 17 to May 1 (Colorado State)

Start indoors
Plant outdoors
Range across the zone
Frost-free season (median)
Spring frost risk (90% to 10%)
Fall frost risk (10% to 90%)

Figure 1. Potatoes in zone 5b. Dark bars: at the zone's median frost dates. Pale bars: across most of the zone's ZIP codes. Hatched blue: where the zone's last and first frosts fall.

Sow outdoors: Apr 17range Apr 7 – May 17
First harvest, roughly: Aug 20125 days from planting1

What each source says, applied to zone 5b

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for potatoes, worked out at zone 5b's median frost dates.

Table 1. Potatoes rules from every source, at zone 5b's median last frost (May 1) and first frost (Oct 11).
Source	What	Rule	Zone 5b median
Colorado State1Used above	Sow outdoors	From 2 wk before to on the last frost	Apr 17 – May 1
Utah State3	Sow outdoors	2 weeks before last frost	Apr 17
Texas A&M (E-502)4	Sow outdoors	4-6 weeks before last frost	Mar 20 – Apr 3
Texas A&M (E-502)4	Plant for fall	14-16 weeks before first frost	Jun 21 – Jul 5

Frost across zone 5b

Last spring frostmedian May 1Full range across the zone: Apr 8 to Jun 21Most of the zone (10th to 90th percentile): Apr 21 to May 17Zone median: May 1
First fall frostmedian Oct 11Full range across the zone: Sep 2 to Oct 29Most of the zone (10th to 90th percentile): Oct 1 to Oct 19Zone median: Oct 11

Frost-free season (median)

Figure 2. Frost dates across zone 5b, from 687 NOAA stations matched to 2,445 ZIP codes.

Planting potatoes with others

Tomatoes Extension guidance Shared late blight: the pathogen overwinters mainly on infected potato tubers and spreads by wind to nearby tomatoes.5 5 6 6

Sources

Colorado State University Extension, Vegetable Planting Guide (CMG GardenNotes #720), reviewed September 2024. Retrieved 2026-11-02.
NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
Utah State University Extension, Suggested Vegetable Planting Dates for Utah, January 2018; revised May 2025. Retrieved 2026-11-02.
Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.
Washington State University Extension (HortSense), Tomato: Late blight (HortSense fact sheet), reviewed Last review date: 2026-08-28. Retrieved 2026-11-02.
University of California Agriculture and Natural Resources (UCCE Master Gardener Program), Companion Planting Chart: Companion planting in the vegetable garden, File dated 2023-09 in URL path; no date printed. Retrieved 2026-11-02.