PlantAlong

When to plant garlic in zone 4a

Plant for fall between Oct 5 and Oct 12. That is 1-2 weeks after zone 4a's median first frost, Sep 281. Across most of zone 4a that date falls between Sep 27 and Oct 18.

Why a range: zone 4a is defined by winter lows, not frost dates. Its ZIP codes have median first frosts from Sep 20 to Oct 42, so a single zone date can be weeks off for you. The rule comes from University of Wisconsin–Madison Division of Extension, Wisconsin Horticulture, written for WI and applied here to zone 4a's frost dates.

Last reviewed
Stations
276
ZIP codes
720
Photo: Chris F / Pexels
These dates use the typical last frost for the whole zone. Your ZIP code gives a closer answer.
  1. Plant for fallWisconsin
  • 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. Garlic in zone 4a. 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.
Fall planting
Oct 51-2 weeks after first frost

Five digits. The calendar is computed on your device.

What each source says, applied to zone 4a

The same frost dates give different answers depending on whose rule you follow. These are all the published rules we hold for garlic, worked out at zone 4a's median frost dates.

Table 1. Garlic rules from every source, at zone 4a's median last frost (May 12) and first frost (Sep 28).
SourceWhatRuleZone 4a median
Minnesota3Plant for fall1-2 weeks after first frostOct 5 – Oct 12
Wisconsin1Used abovePlant for fall1-2 weeks after first frostOct 5 – Oct 12
Texas A&M (E-502)4Plant for fall4-6 weeks before first frostAug 17 – Aug 31

Frost across zone 4a

  1. Last spring frostmedian May 12
  2. First fall frostmedian Sep 28
  • Frost-free season (median)
Figure 2. Frost dates across zone 4a, from 276 NOAA stations matched to 720 ZIP codes.

Sources

  1. University of Wisconsin–Madison Division of Extension, Wisconsin Horticulture, Garlic, Allium sativum, Rev: 10/2023. Retrieved 2026-11-02.
  2. NOAA National Centers for Environmental Information, U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), 2021. Retrieved 2026-11-02.
  3. University of Minnesota Extension, Fruit and Vegetable News blog, Tips for garlic planting season, Page shows October 15, 2026; URL path says 2021/10 (unresolved). Retrieved 2026-11-02.
  4. Texas AgriLife Extension Service, The Texas A&M System, Texas Home Vegetable Gardening Guide (E-502), 2/09. Retrieved 2026-11-02.