Unlikely — Zone Mismatch
pennyroyal (zones 6-9) does not overlap with Minnesota's zone range (3a-5a). Growing outdoors is unlikely without significant protection.
One zone short — what would close it
Pennyroyal is hardy to zone 6, and the warmest ground in Minnesota is zone 5 — 1 zone short. Planted in open ground it will not survive a Minnesota winter. To grow it here, grow pennyroyal in a container and move it under cover for the coldest weeks, or give it a greenhouse.
Season extension and overwintering under cover both work at this margin. How to buy the weeks →
Zone math from 6-9 (plant) against 3-5 (Minnesota). Lift modeled by crop_engine Sprint 20B effective_zone_modifier (+2 zones) via api/fast_sections.py Unlock Engine v2.
Your yard isn't the whole zone.
Minnesota spans zones 3a-5a, but your yard sits in exactly one — and slope, tree cover, and cold-air pockets nudge it further. Enter your address and we'll score pennyroyal against your parcel's actual hardiness, soil, and sun.
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Zone Comparison
Pennyroyal Needs
- USDA Zones: 6-9
- Frost-Free Days: 90+
- Sun: Full Sun
- Mature size: 1.3 ft tall
- Picking window: ~90 days of harvest
- Drought tolerance: Low
Minnesota Has
- USDA Zones: 3a-5a
- Last Hard Freeze (28°F): Apr 19 - Apr 30
- First Hard Freeze (28°F): Oct 10 - Oct 17
- Annual Rainfall: 19-34 inches
- Common Soils: Prairie loam, Clay, Sandy outwash
Plant Zone Range (zones 6-9)
Preferred Soil pH
Plant data: USDA PLANTS Database / Growable Ground plant catalog. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Pennyroyal in Minnesota
The frost window
Across Minnesota, the last spring hard freeze (28°F) clears between Apr 19 and Apr 30, and the first fall hard freeze lands between Oct 10 and Oct 17 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 163-day window you can count on — up to 181 days on a mild site in a kind year. That marks the hard freeze, not the last light frost, so tender transplants usually wait another 2-3 weeks.
When to start the seed
Those dates are when pennyroyal goes out, not when it starts. It is sown under cover about 6 weeks ahead, so counting back from Minnesota's late-side last freeze of Apr 30 is what fixes your sowing date — and a yard that clears frost earlier than the state's late date starts earlier still.
Winter standing
Minnesota runs as cold as USDA zone 3, and no sourced winter-hardiness floor is on record for pennyroyal, so this page does not state whether it overwinters here — and gives no fall establishment date on the strength of a guess. Whether pennyroyal is a permanent planting or a replant-every-spring crop for you turns on your own zone within Minnesota; check its hardiness range against that before treating it as long-lived ground.
Timing tuned to sub-state frost dates — Lake County, not the statewide average.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: USDA PLANTS Database. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
The zone check says pennyroyal does not survive a Minnesota winter in the ground. The season figures below measure a different question — whether it could finish a season here at all — and they only bear on Minnesota under protection.
Frost-free days
Pennyroyal wants 90+ frost-free days; a typical Minnesota site sees ~174 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Pennyroyal needs ~900 GDD (base 50°F) to ripen. The state median runs ~1920 GDD (from PRISM 1991-2020 climate normals), so Minnesota's typical season clears that easily.
GDD and chill-hour figures are computed from PRISM 1991-2020 monthly climate normals; frost-free days from NOAA Regional Climate Centers ACIS, 1991-2020. Each is the state median across its counties (P25/P75 span the within-state spread). Hardiness-zone range is USDA PHZM 2023.
Soil + Drainage Fit
Pennyroyal likes near-neutral soil (pH 5.5-7.5). That's the common-ground band across Minnesota's prairie loam and clay — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 7 — worth knowing before you decide whether a Minnesota soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Minnesota site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Minnesota's soils run mostly loam, but SSURGO maps the series, texture, and drainage under your exact parcel. What matters for pennyroyal is the horizon its roots actually work, not the surface. That map unit, not the state average, decides how pennyroyal performs.
Check your parcel → Source: USDA NRCS SSURGO.
Plant pH and drainage requirements from USDA PLANTS Database. Minnesota soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Pennyroyal in Minnesota — Quick Answer
- Verdict: Unlikely — Zone Mismatch
- Plant Zones: 6-9 (USDA PLANTS Database)
- State Zones: 3a-5a (USDA ARS PHZM 2023)
- Growing Season: 28°F hard freezes about Apr 19 - Apr 30 to Oct 10 - Oct 17 (NOAA Regional Climate Centers ACIS, 1991-2020)
- Days to Maturity: 90 days
What Else to Consider for Pennyroyal in Minnesota
Zone compatibility tells you about winter cold survival — but Minnesota growers also need to think about:
Extreme cold (zone 3a: -40F) limits many species
Short growing season (100-140 frost-free days)
Heavy clay soils in the Red River Valley
Growing pennyroyal here specifically
Pennyroyal wants pH 5.5–7.5 and rates to USDA zones 6–9, but Minnesota's soils are dominantly loam — the fit is decided by your parcel's own map unit, not the state average.
Match pennyroyal to your parcel's SSURGO map unit — test pH and texture, and amend toward its 5.5–7.5 range. How to handle it →
What to actually do about these — and the constraints that apply to every Minnesota grower, not just pennyroyal — is covered on the Minnesota growing guide.
Timing shifts within Minnesota
Minnesota isn't one climate. In Lake County, the last hard freeze (28°F) holds until about May 14 — roughly 23 days later than the recorded state median — so plant pennyroyal to your county's window, not the statewide date.
Pennyroyal needs about 90 days of frost-free season to complete its cycle. Even Lake County — Minnesota’s shortest season at 137 frost-free days — clears that by 47 days, so season length isn’t the constraint anywhere in Minnesota. What varies is your own parcel.
Across Minnesota’s 87 counties the frost-free season runs from 137 days in Lake County to 199 days in Ramsey County — a spread of 62 days, which is why a single statewide planting date misleads. The median Minnesota county sees 174 frost-free days, leaving pennyroyal about 84 days of slack on a typical parcel — room for a second sowing where the season runs long.
County last-freeze dates and frost-free day counts: NOAA Regional Climate Centers ACIS (1991-2020), county 28°F freeze (earlier than the folk 32°F "last frost"). Pennyroyal's 90-day requirement: USDA PLANTS / Growable Ground plant database (minimum frost-free days). A parcel report resolves your address's own frost dates.
Pollinator + Wildlife Value
Pennyroyal draws honeybees, native bees, and butterflies (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, pennyroyal can only work that bloom inside Minnesota's frost window — roughly 174 days, opening after the last 28°F freeze (Apr 19 - Apr 30) and closing at the first (Oct 10 - Oct 17), per NOAA Regional Climate Centers ACIS, 1991-2020.
Good to Know Before You Plant Pennyroyal
Pennyroyal is listed as toxic to dogs, cats (all) at a severe level (ASPCA). Most listed plants only cause brief upset — a raised bed or a fenced corner usually keeps curious pets clear.
Recommended Pennyroyal Varieties for Minnesota
Minnesota publishes no state variety trial for pennyroyal, so we won't invent a "best for Minnesota" list. Choose types rated to your USDA hardiness zone (3a-5a), and confirm winter survival and drainage against your own parcel.
Minnesota Cooperative Extension
For Minnesota-specific cultivar recommendations, planting calendars, and pest pressure for pennyroyal, the canonical source is University of Minnesota Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Pennyroyal native to Minnesota?
No — the USDA PLANTS Database lists Pennyroyal as introduced rather than native in the Lower 48, so it is not part of Minnesota's native flora. It grows here as a garden plant; pairing it with a few Minnesota natives keeps local pollinators fed too.
Looking for plants that belong here? The Minnesota growing guide lists USDA-documented natives for the state.
Native-range data: USDA PLANTS Database state-distribution records, accessed 2026-07-01.
Common Questions About Growing Pennyroyal in Minnesota
When can I plant Pennyroyal in Minnesota?
Minnesota's last spring hard freeze (28°F) clears between Apr 19 and Apr 30, and the first fall hard freeze lands between Oct 10 and Oct 17 (NOAA Regional Climate Centers ACIS, 1991-2020). No sourced winter-hardiness floor is on record for Pennyroyal, so this page does not state whether it overwinters in Minnesota and publishes no fall establishment date for it — check its hardiness range against your own zone before treating it as a permanent planting.
What hardiness zone is Pennyroyal grown in across Minnesota?
Minnesota spans USDA hardiness zones 3a-5a (USDA ARS PHZM 2023). Pennyroyal carries a range of zones 6-9, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Minnesota site have?
A typical Minnesota site sees ~174 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Pennyroyal needs 90+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date. In cooler counties like Lake, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Pennyroyal native to Minnesota?
No — the USDA PLANTS Database lists Pennyroyal as introduced rather than native in the Lower 48, so it is not part of Minnesota's native flora. It grows here as a garden plant; pairing it with a few Minnesota natives keeps local pollinators fed too.
How should I amend the soil for Pennyroyal in Minnesota?
Pennyroyal prefers pH 5.5-7.5 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Minnesota soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Pennyroyal actually grow on my specific land in Minnesota?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores pennyroyal against your address's exact soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in Minnesota
State-level data is a sketch. Your Growable Ground report scores pennyroyal against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Minnesota pennyroyal averages can't show:
We read public map data around Minnesota — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Minnesota pennyroyal average
Explore More
Growing guides for pennyroyal
Analysis by the Growable Ground research team, grounded in USDA PLANTS, USDA NRCS SSURGO, NOAA Climate Normals (1991-2020), and named Cooperative Extension sources. How we know →
Cite this dataset
Kirchick, M. (2026). Growable Ground Plant Database [Data set]. Zenodo. https://doi.org/10.5281/zenodo.21435643
Licensed CC BY-NC 4.0. DOI 10.5281/zenodo.21435643
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