Yes — Strong Match
mustard cover crop (zones 3-10) covers every zone Idaho contains (3b-8a), so hardiness is not what limits it anywhere in the state.
Mustard Cover Crop in Idaho — the short answer
Mustard Cover Crop in Idaho: hardy in zones 3–10, full sun, against a state median of ~160 frost-free days.
- Plant zones
- 3-10
- 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
- Idaho zones
- 3b-8a
- USDA PHZM 2023
- Frost window
- Apr 26 - May 17 – Oct 1 - Oct 17
- NOAA RCC ACIS 1991-2020, 28°F
- Shortest county season
- 94 days
- NOAA Regional Climate Centers ACIS, 1991-2020, county 28°F killing freeze
- Days to maturity
- 50 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.
Mustard Cover Crop is grown as an annual, so your winter zone isn't the deciding factor — your frost-free window is. A typical Idaho site runs ~160 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 mustard cover crop 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
Idaho is not one climate
A single Idaho answer averages 44 counties whose growing seasons are 122 days apart — from 94 frost-free days in Valley County to 216 in Nez Perce County. Which end of that your land sits nearer changes what mustard cover crop can finish before the first hard freeze.
The middle half of 44 counties runs 133–174 days, with a median of 159 days — a 122-day span end to end.
Measured across 44 Idaho 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 Idaho Fits Best
Even within Idaho's zones 3b-8a, county microclimates differ enough to change what thrives. These counties carry the closest zone match for mustard cover crop (USDA PHZM 2023):
Zone Comparison
Mustard Cover Crop Needs
- USDA Zones: 3-10
- Frost-Free Days: 110+
- Sun: Full Sun
- Mature size: 4 ft tall
- Drought tolerance: Medium
Idaho Has
- USDA Zones: 3b-8a
- Last Hard Freeze (28°F): Apr 26 - May 17
- First Hard Freeze (28°F): Oct 1 - Oct 17
- Annual Rainfall: 8-35 inches
- Common Soils: Volcanic ash, Silt loam, Sandy loam
Plant Zone Range (zones 3-10)
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 Mustard Cover Crop in Idaho
The frost window
Across Idaho, the last spring hard freeze (28°F) clears between Apr 26 and May 17, and the first fall hard freeze lands between Oct 1 and Oct 17 (NOAA Regional Climate Centers ACIS, 1991-2020). Counting from the latest last freeze to the earliest first freeze, that's a 137-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
Mustard Cover Crop takes cold down to about 25°F before a freeze kills it (FAO ECOCROP), so you can plant on the early side of Idaho'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
Mustard Cover Crop is direct-sown where it grows rather than started under cover, so there is no seed-tray head start to bank — Idaho'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 50 days to maturity (Growable Ground Plant Database), counting from the last hard freeze it ripens with 87 days to spare even in Idaho's tightest freeze scenario — room for a later start or a second sowing.
Timing tuned to sub-state frost dates — Valley County, not the statewide average.
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 mustard cover crop survives winter here. Whether the season is long enough — and warm enough — is a different question.
Frost-free days
Mustard Cover Crop wants 110+ frost-free days; a typical Idaho site sees ~160 (NOAA Regional Climate Centers ACIS, 1991-2020). That leaves a workable window — start indoors to bank time.
Growing degree days
Mustard Cover Crop needs ~900 GDD (base 50°F) to ripen. The state median runs ~1187 GDD (from PRISM 1991-2020 climate normals), so Idaho'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
Mustard Cover Crop tolerates a wide pH range (pH 5.5-8.5) — 3 units, acid ground through alkaline — so soil acidity is rarely what limits it in Idaho. A soil test is still worth having, but for what else it tells you about this site, not to clear this plant. It will grow across that whole span, but it does best between pH 6.5 and 7.5 — worth knowing before you decide whether a Idaho soil test result is a problem or just a number. Drainage matters: this plant wants well (dry spells). If your Idaho site is heavier clay or sits in a low spot, raised beds or amendment with compost solve it.
Your land, not the state average
Whether mustard cover crop is safe to eat from Idaho soil is a block-by-block question, not a town-wide one — 21,100 documented contamination sites mean levels spike on some parcels and not the one next door. Mustard Cover Crop roots to about 19 inches, so it is the top 19 inches under your address that decide what it takes up, so only a test on your address settles it.
Check your parcel → Source: USDA NRCS SSURGO + EPA/state contamination databases.
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. Idaho soil profile from USDA NRCS SSURGO. Site-specific verification: a 30-minute soil test from your local Extension lab.
What Else to Consider for Mustard Cover Crop in Idaho
Zone compatibility tells you about winter cold survival — but Idaho growers also need to think about:
Short growing season at higher elevations
Arid conditions require irrigation in most of the state
Cold winter snaps can reach -30F in mountain valleys
Growing mustard cover crop here specifically
Mustard Cover Crop grows its edible leaves in the soil itself, so on any of Idaho's 21,100 documented contamination sites it can carry up lead you'd then eat.
Keep mustard cover crop in raised beds of screened clean soil and confirm your parcel's lead level before the first crop. How to handle it →
What to actually do about these — and the constraints that apply to every Idaho grower, not just mustard cover crop — is covered on the Idaho growing guide.
Timing shifts within Idaho
Idaho isn't one climate. In Valley County, the last hard freeze (28°F) holds until about Jun 14 — roughly 42 days later than the recorded state median — so plant mustard cover crop to your county's window, not the statewide date.
Mustard Cover Crop needs about 110 days of frost-free season to complete its cycle. 42 of Idaho’s 44 counties give it that outright. The tightest that does is Idaho County at 110 frost-free days — 0 to spare. Below that line you are transplanting or extending the season, not direct-sowing.
Across Idaho’s 44 counties the frost-free season runs from 94 days in Valley County to 216 days in Nez Perce County — a spread of 122 days, which is why a single statewide planting date misleads. The median Idaho county sees 160 frost-free days, leaving mustard cover crop about 50 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"). Mustard Cover Crop'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
Mustard Cover Crop draws honeybees and native bees (moderate value, Growable Ground Plant Database). Planting it near vegetable beds can lift fruit set on neighboring crops. Outdoors, mustard cover crop can only work that bloom inside Idaho's frost window — roughly 160 days, opening after the last 28°F freeze (Apr 26 - May 17) and closing at the first (Oct 1 - Oct 17), per NOAA Regional Climate Centers ACIS, 1991-2020.
Idaho Cooperative Extension
For Idaho-specific cultivar recommendations, planting calendars, and pest pressure for mustard cover crop, the canonical source is University of Idaho Extension. Their fact sheets carry the local trial data we can't generalize across 50 states.
Is Mustard Cover Crop native to Idaho?
No — the USDA PLANTS Database lists Mustard Cover Crop as introduced rather than native in the Lower 48, so it is not part of Idaho's native flora. It grows here as a garden plant; pairing it with a few Idaho natives keeps local pollinators fed too.
Looking for plants that belong here? The Idaho 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 Mustard Cover Crop in Idaho
When can I plant Mustard Cover Crop in Idaho?
Idaho's last spring hard freeze (28°F) clears between Apr 26 and May 17, and the first fall hard freeze lands between Oct 1 and Oct 17 (NOAA Regional Climate Centers ACIS, 1991-2020). Mustard Cover Crop takes cold to about 25°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 Mustard Cover Crop mature before first frost in Idaho?
Yes — Mustard Cover Crop matures in 50 days (Growable Ground Plant Database), and Idaho's dependable hard-freeze-free window runs 137 days (NOAA Regional Climate Centers ACIS, 1991-2020), leaving 87 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 Mustard Cover Crop grown in across Idaho?
Idaho spans USDA hardiness zones 3b-8a (USDA ARS PHZM 2023). Mustard Cover Crop carries a range of zones 3-10, so the overlap zones are where outdoor growing is most reliable.
How many frost-free days does a typical Idaho site have?
A typical Idaho site sees ~160 frost-free days per year (derived from NOAA Regional Climate Centers ACIS, 1991-2020). Mustard Cover Crop needs 110+ 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 Valley, the freeze-free season runs shorter than the state average, so verify your own county's window.
Is Mustard Cover Crop native to Idaho?
No — the USDA PLANTS Database lists Mustard Cover Crop as introduced rather than native in the Lower 48, so it is not part of Idaho's native flora. It grows here as a garden plant; pairing it with a few Idaho natives keeps local pollinators fed too.
How should I amend the soil for Mustard Cover Crop in Idaho?
Mustard Cover Crop tolerates pH 5.5-8.5 and well (dry spells) drainage (FAO ECOCROP). That is a 3-unit span, acid ground through alkaline, so pH is rarely what limits this plant on a Idaho site — amend for drainage and organic matter first.
Will Mustard Cover Crop actually grow on my specific land in Idaho?
State-level zone + climate data is a sketch. A Growable Ground parcel report scores mustard cover crop 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 Idaho
State-level data is a sketch. Your Growable Ground report scores mustard cover crop against your parcel's exact soil, sun, drainage, and frost data — not zone averages.
Three things about your lot that Idaho mustard cover crop averages can't show:
We read public map data around Idaho — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Idaho mustard cover crop average
Explore More
Growing guides for mustard cover crop
Explore Idaho county by county
Idaho carries 44 counties with their own USDA zone — a sample of the growing pages for mustard cover crop there:
Where else mustard cover crop grows
Mustard Cover Crop's zone band crosses state lines — these are the states closest to Idaho 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 Idaho
Idaho has a growing page for 893 plants — a rotating sample of the rest of the shelf.
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
Last updated: