Generally — Most Areas
black seed (zones 5-10) suits most of Colorado (3b-7b) — zones 5-7 are in range, and the rest of the state is the exception.
Black Seed in Colorado — the short answer
Black Seed in Colorado: hardy in zones 5–10, full sun, against a state median of ~155 frost-free days.
- Plant zones
- 5-10
- Manual horticultural correction (source not retained); NC State Extension and Missouri Botanical Garden, with the remaining rows from other published sources or Growable Ground compilation
- Colorado zones
- 3b-7b
- USDA PHZM 2023
- Frost window
- Apr 25 - May 19 – Sep 29 - Oct 16
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 85 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 100 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.
Black Seed is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Colorado site runs ~155 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 black seed 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.
No card required · your full report in seconds
Colorado is not one climate
A single Colorado answer averages 64 counties whose growing seasons are 124 days apart — from 85 frost-free days in Chaffee County to 209 in Mesa County. Which end of that your land sits nearer changes what black seed can finish before the first hard freeze.
The middle half of 64 counties runs 132–174 days, with a median of 150 days — a 124-day span end to end.
Measured across 64 Colorado counties. NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze. 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.
Where in Colorado Fits Best
Black Seed is rated for zones 5–10 — a cold floor USDA puts at -20 to -10°F. Against Colorado’s 64 counties that band holds in 59 of them, and the line runs at Chaffee County (zone 5a), the coldest county still inside it.
Inside zones 5–10
59 counties
- Clear Creek County · zone 5a
- Custer County · zone 5a
- Grand County · zone 5a
3 of 59 shown
Below the zone 5 floor
5 counties
- Alamosa County · zone 4b
- Jackson County · zone 4b
- Park County · zone 4b
3 of 5 shown
Winter cold is the limit here — the same plant works in a container that comes under cover.
County hardiness zones: USDA Plant Hardiness Zone Map (PHZM) 2023, per county. A zone is a 10°F band of average annual extreme minimum temperature, so the floor above is the band the plant's rating denotes, not a single measured kill point. Slope, shelter and cold-air drainage routinely move a site half a zone either way from its county figure — which is the part only your address resolves.
Even within Colorado's zones 3b-7b, county microclimates differ enough to change what thrives. These counties carry the closest zone match for black seed (USDA PHZM 2023):
Zone Comparison
Black Seed Needs
- USDA Zones: 5-10
- Frost-Free Days: 90+
- Sun: Full Sun
- Mature size: 1.3 ft tall
- Picking window: ~21 days of harvest
- Drought tolerance: Medium
Colorado Has
- USDA Zones: 3b-7b
- Last Hard Freeze (28°F): Apr 25 - May 19
- First Hard Freeze (28°F): Sep 29 - Oct 16
- Annual Rainfall: 7-20 inches
- Common Soils: Sandy loam, Clay loam, Alkaline caliche
Plant Zone Range (zones 5-10)
Preferred Soil pH
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 Black Seed in Colorado
The frost window
Across Colorado, the last spring hard freeze (28°F) clears between Apr 25 and May 19, and the first fall hard freeze lands between Sep 29 and Oct 16 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 133-day window you can count on — up to 174 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.
Frost hardiness
Black Seed takes cold down to about 28°F before a freeze kills it (FAO ECOCROP), so you can plant on the early side of Colorado's window — even a few weeks before the final hard freeze. That is the point where cold damages growing tissue, not a winter-survival floor — an established perennial comes through far colder while dormant, which is what its hardiness zone tells you.
When to start the seed
Black Seed is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Colorado'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 100 days to maturity (Growable Ground Plant Database), counting from the last hard freeze it ripens with 33 days to spare even in Colorado'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
The zone check says black seed survives winter in part of Colorado, not across all of it. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Black Seed wants 90+ frost-free days; a typical Colorado site sees ~155 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves comfortable headroom for succession planting.
Growing degree days
Black Seed needs ~1500 GDD (base 50°F) to ripen. The state median runs ~2083 GDD (from PRISM 1991-2020 climate normals), so Colorado'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
Black Seed likes near-neutral soil (pH 5.5-8). That's the common-ground band across Colorado's sandy loam and clay loam — a soil test confirms it for your site. It will grow across that whole span, but it does best between pH 6 and 7.5 — worth knowing before you decide whether a Colorado soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Colorado site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
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. Colorado soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
Before you plant black seed 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 black seed goes in. What follows is Colorado’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 Colorado — and how to grow with it.
We checked the federal record across Colorado — 29,759 documented sites across 8 of the 9 source types we track.
The most significant on record: 281 Superfund sites. Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
Colorado 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 with clean imported soil grow well almost anywhere in the meantime.
Sources Checked
across Colorado
Severity Distribution
across Colorado
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Colorado, Mining runs higher than the national average — 5,049 sites across Colorado. It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Mining: Mining sites — both historic and active — can leach heavy metals (arsenic, lead, cadmium, mercury) into soil and water for centuries after operations cease.
Test soil for heavy metals (lead, arsenic, cadmium, mercury) — this is essential near any mining site.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What Else to Consider for Black Seed in Colorado
Zone compatibility tells you about winter cold survival — but Colorado growers also need to think about:
Low annual rainfall (7-20 inches) means irrigation is essential nearly everywhere
High altitude UV and temperature swings stress plants
Very short growing season at elevation (60-90 frost-free days above 8,000 ft)
Alkaline soils (pH 7.5-8.5) limit acid-loving plants without amendment
What to actually do about these — and the constraints that apply to every Colorado grower, not just black seed — is covered on the Colorado growing guide.
Timing shifts within Colorado
Black Seed needs about 90 days of frost-free season to complete its cycle. 63 of Colorado’s 64 counties give it that outright. The tightest that does is Hinsdale County at 97 frost-free days — 7 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
Across Colorado’s 64 counties the frost-free season runs from 85 days in Chaffee County to 209 days in Mesa County — a spread of 124 days, which is why a single statewide planting date misleads. The median Colorado county sees 155 frost-free days, leaving black seed about 65 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"). Black Seed'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
Black Seed draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, black seed can only work that bloom inside Colorado's frost window — roughly 155 days, opening after the last 28°F freeze (Apr 25 - May 19) and closing at the first (Sep 29 - Oct 16), per NOAA Regional Climate Centers ACIS, 1991-2020.
Colorado Cooperative Extension
For Colorado-specific cultivar recommendations, planting calendars, and pest pressure for black seed, the canonical source is Colorado State University Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Black Seed native to Colorado?
No — the USDA PLANTS Database lists Black Seed as introduced rather than native in the Lower 48, so it is not part of Colorado's native flora. It grows here as a garden plant; pairing it with a few Colorado natives keeps local pollinators fed too.
Looking for plants that belong here? The Colorado 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 Black Seed in Colorado
When can I plant Black Seed in Colorado?
Colorado's last spring hard freeze (28°F) clears between Apr 25 and May 19, and the first fall hard freeze lands between Sep 29 and Oct 16 (NOAA Regional Climate Centers ACIS, 1991-2020). Black Seed takes cold to about 28°F before a freeze kills it (FAO ECOCROP — the point where cold damages growing tissue, not a winter-survival floor), so plant on the early side of that window — even ahead of the final hard freeze.
Can Black Seed mature before first frost in Colorado?
Yes — Black Seed matures in 100 days (Growable Ground Plant Database), and Colorado's dependable hard-freeze-free window runs 133 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 33 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 Black Seed grown in across Colorado?
Colorado spans USDA hardiness zones 3b-7b (USDA ARS PHZM 2023). Black Seed carries a range of zones 5-10, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Colorado site have?
A typical Colorado site sees ~155 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Black Seed needs 90+ frost-free days, so check whether your local microclimate runs above or below the state average before settling on a planting date.
Is Black Seed native to Colorado?
No — the USDA PLANTS Database lists Black Seed as introduced rather than native in the Lower 48, so it is not part of Colorado's native flora. It grows here as a garden plant; pairing it with a few Colorado natives keeps local pollinators fed too.
How should I amend the soil for Black Seed in Colorado?
Black Seed prefers pH 5.5-8 and well (dry spells) drainage (Growable Ground Plant Database). That sits in the common-ground band across Colorado soils — a 30-minute soil test from a local Extension lab confirms it for your specific site.
Will Black Seed actually grow on my specific land in Colorado?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores black seed 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 Colorado
State-level data is a sketch. Your Growable Ground report scores black seed against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Colorado black seed averages can't show:
We read public map data around Colorado — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Colorado black seed average
Explore More
Growing guides for black seed
Explore Colorado county by county
Colorado carries 64 counties with their own USDA zone — a sample of the growing pages for black seed there:
Where else black seed grows
Black Seed's zone band crosses state lines — these are the states closest to Colorado 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 Colorado
Colorado has a growing page for 893 plants — a rotating sample of the rest of the shelf.
Last updated: