Generally — Most Areas
milk thistle is grown as an annual, so season length decides it here, not a winter zone. North Dakota's typical season runs ~157 frost-free days against the ~110 milk thistle needs — a workable window, but start indoors to bank time.
Milk Thistle in North Dakota — the short answer
Milk Thistle in North Dakota: grown in zones 5–9, full sun, against a state median of ~157 frost-free days.
- Plant zones
- Grown as an annual — see the growing season
- Growing season, not a hardiness zone
- North Dakota zones
- 3b-4b
- USDA PHZM 2023
- Frost window
- Apr 30 - May 6 – Oct 4 - Oct 9
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 141 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 120 days
- Growable Ground Plant Database
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS and university Extension sources — per-field provenance varies and is published with the dataset.
Your yard isn't the whole zone.
Milk Thistle is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical North Dakota site runs ~157 frost-free days, but that is a state median, not your yard: slope, trees, and low spots move the last-frost date across a single parcel. Enter your address and we'll score milk thistle against your land's actual frost dates, sun, and soil.
We read public map data for this spot — soil, climate, flood, and parcel records. How we handle your address.
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North Dakota is not one climate
North Dakota’s winter-low ladder runs across 53 counties, from zone 3.5 in Bottineau County to zone 4.5 in Stutsman County. That is 10°F between the two counties’ average coldest night — the difference between milk thistle overwintering in the ground and coming under cover.
The middle half of 53 counties runs 4–4 zones, with a median of 4 zones — a 1-zone span end to end.
Measured across 53 North Dakota counties. USDA PHZM 2023, per county. Quartiles are order statistics — every figure shown is a value a real county recorded, not an interpolation. Your own site sits somewhere inside this range; a parcel report resolves where.
Zone Comparison
Milk Thistle Needs
- USDA Zones: 5-9
- Frost-Free Days: 110+
- Sun: Full Sun
- Mature size: 4 ft tallWe haven't confirmed this against a published source yet.
- Picking window: ~30 days of harvestWe haven't confirmed this against a published source yet.
- Drought tolerance: HighWe haven't confirmed this against a published source yet.
North Dakota Has
- USDA Zones: 3b-4b
- Last Hard Freeze (28°F): Apr 30 - May 6
- First Hard Freeze (28°F): Oct 4 - Oct 9
- Annual Rainfall: 14-22 inches
- Common Soils: Prairie loam, Clay (Red River Valley), Sandy loam
Plant Zone Range (zones 5-9)
Preferred Soil pH
We haven't confirmed this against a published source yet.
Plant data: Growable Ground Plant Database, compiled from FAO ECOCROP, USDA PLANTS, and university Extension sources — per-field provenance varies and is published with the dataset. State data: USDA ARS PHZM 2023, NOAA Climate Normals, NRCS SSURGO.
When to Plant Milk Thistle in North Dakota
The frost window
Across North Dakota, the last spring hard freeze (28°F) clears between Apr 30 and May 6, and the first fall hard freeze lands between Oct 4 and Oct 9 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 151-day window you can count on — up to 162 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
Milk Thistle is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — North Dakota's dates above are the whole calendar for it. That makes the last-freeze date the binding constraint, and a warmer pocket of your own yard is worth more to this crop than it is to a transplanted one.
Days to maturity vs. the window
At 120 days to maturity (Growable Ground Plant Database), counting from the last hard freeze it ripens with 31 days to spare even in North Dakota's tightest freeze scenario — room for a later start or a second sowing.
Frost window: NOAA Climate Normals 1991-2020. Plant timing fields: Growable Ground Plant Database — frost-free days from FAO ECOCROP, days to harvest from university Extension production guides, and growing-degree-day and chill-hour minimums that are compilation estimates rather than published figures. Your site's own frost dates can run earlier or later than the state range — a parcel report pins them down.
Growing Season Fit
Frost-free days
Milk Thistle wants 110+ frost-free days; a typical North Dakota site sees ~157 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves a workable window — start indoors to bank time.
Growing degree days
Milk Thistle needs ~1000 GDD (base 50°F) to ripen. We haven't confirmed this against a published source yet. The state median runs ~1913 GDD (from PRISM 1991-2020 climate normals), so North Dakota'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
Milk Thistle likes near-neutral soil (pH 5.5-8). That's the common-ground band across North Dakota's prairie loam and clay (red river valley) — a soil test confirms it for your site. Drainage matters: this plant wants well (dry spells). If your North Dakota site is heavier clay or sits in a low spot, a raised bed lifts the roots above wet ground, or work in compost. pH range: We haven't confirmed this against a published source yet.
Plant pH requirements: FAO ECOCROP and USDA PLANTS, with the remaining rows from other published sources or Growable Ground compilation. Drainage: FAO ECOCROP, with the remaining rows from other published sources or Growable Ground compilation. North Dakota soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant milk thistle for food
Anything you grow to eat takes up what is in the ground it grows in, so what is on record near you is worth knowing before milk thistle goes in. What follows is North Dakota’s documented federal record at state scale — a screening signal, not a soil test, and not a statement about any one lot.
Safe to Grow Here?
What the federal record shows across North Dakota — and how to grow with it.
We checked the federal record across North Dakota — 4,130 documented sites across 5 of the 8 source types we track.
The most significant on record: 22 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
North Dakota carries one of the heavier federal records we track — and that's not a verdict on your yard. Proximity to a documented site is information, not a diagnosis: nothing here says any particular parcel is affected. It does earn one concrete step — before food beds go in the ground, a professional soil test tells you exactly what you're working with, and raised beds of imported, lab-tested soil grow well almost anywhere in the meantime.
Sources Checked
across North Dakota
Severity Distribution
across North Dakota
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around North Dakota, Brownfields runs higher than the national average — 345 sites across North Dakota. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Brownfields: Brownfield sites are former commercial or industrial properties that EPA’s Brownfields program (ACRES) has assessed or funded cleanup on.
Contact the EPA Brownfields program or the state cleanup agency for this site’s actual assessment/remediation status — ACRES itself does not publish one we can read per site.
Sources: EPA, USGS — 950K documented sites tracked nationwide across 8 federal source types.
What Else to Consider for Milk Thistle in North Dakota
The zone range tells you where milk thistle is grown — but North Dakota growers also need to think about:
Extreme cold (-40F) and short growing season
Persistent wind desiccates plants
Low rainfall in western ND
What to actually do about these — and the constraints that apply to every North Dakota grower, not just milk thistle — is covered on the North Dakota growing guide.
Timing shifts within North Dakota
Milk Thistle needs about 110 days of frost-free season to complete its cycle. Even Bottineau County — North Dakota’s shortest season at 141 frost-free days — clears that by 31 days, so season length isn’t the constraint anywhere in North Dakota. What varies is your own parcel.
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"). Milk Thistle's 110-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
Milk Thistle draws honeybees, native bees, and butterflies (moderate value). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, milk thistle can only work that bloom inside North Dakota's frost window — roughly 157 days, opening after the last 28°F freeze (Apr 30 - May 6) and closing at the first (Oct 4 - Oct 9), per NOAA Regional Climate Centers ACIS, 1991-2020. Pollinator value: We haven't confirmed this against a published source yet.
North Dakota Cooperative Extension
For North Dakota-specific cultivar recommendations, planting calendars, and pest pressure for milk thistle, the canonical source is NDSU Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Milk Thistle native to North Dakota?
No — the USDA PLANTS Database lists Milk Thistle as introduced rather than native in the Lower 48, so it is not part of North Dakota's native flora. It grows here as a garden plant; pairing it with a few North Dakota natives keeps local pollinators fed too.
Looking for plants that belong here? The North Dakota growing guide lists plants that USDA PLANTS records growing in North Dakota and that Kew and NatureServe Explorer both list in its native range, leaving out any that NatureServe flags as exotic there or that our audit holds.
State records: USDA PLANTS Database state-distribution data (presence, not state-level nativity), accessed 2026-10-19.
Common Questions About Growing Milk Thistle in North Dakota
When can I plant Milk Thistle in North Dakota?
North Dakota's last spring hard freeze (28°F) clears between Apr 30 and May 6, and the first fall hard freeze lands between Oct 4 and Oct 9 (NOAA Regional Climate Centers ACIS, 1991-2020). Time outdoor planting to after the last hard freeze for your specific site — a further two to three weeks for anything tender — and count back from those dates for transplant scheduling.
Can Milk Thistle mature before first frost in North Dakota?
Yes — Milk Thistle matures in 120 days (Growable Ground Plant Database), and North Dakota's dependable hard-freeze-free window runs 151 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 31 days of margin. Plant once the last hard freeze has passed — two to three weeks later for anything tender — and it ripens ahead of the first fall freeze.
What hardiness zone is Milk Thistle grown in across North Dakota?
North Dakota spans USDA hardiness zones 3b-4b (USDA ARS PHZM 2023). Milk Thistle carries a range of zones 5-9, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical North Dakota site have?
A typical North Dakota site sees ~157 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Milk Thistle needs 110+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Milk Thistle native to North Dakota?
No — the USDA PLANTS Database lists Milk Thistle as introduced rather than native in the Lower 48, so it is not part of North Dakota's native flora. It grows here as a garden plant; pairing it with a few North Dakota natives keeps local pollinators fed too.
How should I amend the soil for Milk Thistle in North Dakota?
Milk Thistle prefers pH 5.5-8 and well (dry spells) drainage. We haven't confirmed this against a published source yet. That sits in the common-ground band across North Dakota soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Milk Thistle actually grow on my specific land in North Dakota?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores milk thistle against your address's mapped soil pH, drainage, sun, and frost-date data drawn from USDA SSURGO, NOAA, and PRISM — not state averages.
Check your specific parcel in North Dakota
State-level data is a sketch. Your Growable Ground report scores milk thistle against your land's mapped soil, modelled sun, drainage, and frost data — not zone averages.
Three things about your lot that North Dakota milk thistle averages can't show:
We read public map data around North Dakota — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the North Dakota milk thistle average
Explore More
Growing guides for milk thistle
Explore North Dakota county by county
North Dakota carries 53 counties with their own USDA zone — a sample of the growing pages for milk thistle there:
Where else milk thistle grows
Milk Thistle's zone band crosses state lines — these are the states closest to North Dakota in winter climate where it also has a page, plus the far ends of its range. Each one re-answers the question with that state's own record.
More to grow in North Dakota
North Dakota has a growing page for 745 plants — a rotating sample of the rest of the shelf.
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