Maturity Group & Ripen Before the Frost
Matches latitude
Maturity-group choice is buried in extension PDFs. Drop your latitude, sowing date and first-frost date and this tool reads the best-adapted maturity group off an adaptation ruler, then shows whether your variety ripens safely inside the frost-free corridor — with the exact margin in days.
Your location & window
Next: this 120-day variety fits — keep MG III class material and sow by Jun 5 at the latest to hold the 7-day safety buffer.
Soybean MG follows the USDA / university-extension adaptation map (MG falls as latitude rises). The 7-day buffer guards against an early frost and slow late-season dry-down. Frost-free days and exact maturity vary with the season — treat as a planning estimate.
Maturity group — key facts
- MG range
- 000 (earliest) → IX (latest)
- MG @ 42°N
- ≈ MG II (Corn Belt)
- MG @ 35°N
- ≈ MG V
- Frost margin
- first frost − maturity date
- Safety buffer
- ripen ≥ 7 days before frost
- Latest sow
- frost − duration − 7 days
- Maize scale
- FAO 100 (early) → 700 (late)
- Privacy
- Runs in your browser; nothing uploaded
Soybean maturity-group adaptation by latitude
From the standard USDA / university-extension soybean maturity-group adaptation map. The best-adapted full-season group falls as latitude rises; relative days are emergence-to-maturity.
| Maturity group | Adapted latitude (°) | Relative days | Region |
|---|---|---|---|
| MG 000 | 49–49+ | 80–95 d | Far-north / prairie — very short season |
| MG 00 | 47–49 | 88–100 d | Northern prairie / S. Canada |
| MG 0 | 45–47 | 95–108 d | N. Dakota / S. Manitoba band |
| MG I | 43–45 | 100–113 d | S. Dakota / S. Minnesota |
| MG II | 41–43 | 108–120 d | Iowa / Nebraska Corn Belt |
| MG III | 39–41 | 115–128 d | C. Illinois / Indiana |
| MG IV | 36–39 | 122–135 d | S. Illinois / Missouri / Kansas |
| MG V | 33–36 | 130–143 d | Tennessee / N. Mississippi / N. India plains |
| MG VI | 31–33 | 138–150 d | Mississippi Delta / C. India |
| MG VII | 29–31 | 145–158 d | Gulf Coast / Deccan |
| MG VIII | 26–29 | 150–165 d | S. Texas / Florida / S. India |
| MG IX | 0–26 | 158–175 d | Tropical / sub-tropical (Brazil, S. India) |
Rice, wheat & maize duration classes
| Crop | Class | Days (sow→maturity) | FAO no. |
|---|---|---|---|
| rice | Very short (early) | 90–105 d (≈100) | — |
| Short duration | 105–120 d (≈115) | — | |
| Medium duration | 120–140 d (≈130) | — | |
| Long duration | 140–160 d (≈150) | — | |
| wheat | Early (timely-sown short) | 100–115 d (≈110) | — |
| Medium / timely-sown | 120–135 d (≈128) | — | |
| Long (full-season) | 140–155 d (≈148) | — | |
| maize | Very early (FAO 100–200) | 80–95 d (≈88) | 100–200 |
| Early (FAO 300) | 95–110 d (≈103) | 300 | |
| Medium (FAO 400–500) | 110–125 d (≈118) | 400–500 | |
| Late (FAO 600–700) | 125–145 d (≈135) | 600–700 |
Sources: USDA / extension soybean MG adaptation maps; ICAR varietal duration tables; FAO maize maturity classification.
Why the right maturity group decides whether you harvest a crop
A variety only yields if it can finish its life cycle inside the season you have. Plant a maturity group that is too long for your latitude and frost-free window and the crop is caught green by the first frost; plant one too short and you leave yield potential — and growing days — on the table. Soybean is photoperiod-sensitive, so the adapted group changes with latitude, while rice, wheat and maize are matched by duration class against the days from sowing to your season-end.
This tool turns that decision into one screen: a latitude ruler that names your maturity group, and a frost-free corridor that shows your variety's duration bar sitting safely inside the season — or spilling past the frost line. Use it to choose a variety, to decide how late you can still plant, and to switch to an earlier group for double-cropping. Pair it with the Nursery-to-Field Scheduler and the Intercrop Competition Index for a full crop-planning workflow.
Frequently Asked Questions
Which soybean maturity group should I plant at my latitude?+
As a rule of thumb, the best-adapted full-season maturity group falls as you move north. Around 42°N (Iowa) MG II is well-adapted; near 40°N (central Illinois) MG III; around 35°N (Tennessee) MG V; and along the Gulf at 30°N up to MG VII. This tool drops a pin on the latitude ruler and reads off the band for you, then checks that your chosen variety's duration still ripens before your first frost.
How is the frost margin calculated?+
The tool adds your variety's duration (sowing-to-maturity days) to the sowing date to get the maturity date, then subtracts that from your first-frost date. The result is the margin in days: a positive margin means the crop ripens before frost, a negative one means it is caught. We flag the result safe when the margin is at least 7 days, tight from 0 to 7 days, and risky below 0.
What does maturity group actually mean?+
Maturity group (MG) is a relative ranking of how long a soybean variety takes to mature under a given photoperiod and latitude. MG 000 is the earliest (very short season, far north) and MG IX the latest (long season, tropics). Because soybean is photoperiod-sensitive, an MG that fits at 42°N will mature far too early or too late if grown well outside its adapted band, which is why the latitude match matters.
Is MG II good for my area?+
MG II is the standard full-season choice for roughly 41–43°N — the heart of the US Corn Belt (much of Iowa, Nebraska and southern Minnesota). If you farm noticeably north of that, an earlier group (MG I, 0 or 00) will be safer; well south of it, MG III–IV captures more season. Enter your latitude and the tool confirms whether MG II sits in your band.
How late can I plant and still ripen before frost?+
The tool computes the latest safe sowing date as your first-frost date minus the variety's duration minus a 7-day safety buffer. Sow after that and the crop risks being caught by frost while still filling. For late or double-crop planting, switch to an earlier maturity group so the shorter duration fits the days you have left.
Does this work for rice, wheat and maize too?+
Yes. Choose the crop and the tool shows duration classes instead of soybean MGs: rice as very-short to long duration (about 100–150 days), wheat as early/medium/long, and maize on the FAO maturity-number scale (FAO 100–700, roughly 88–135 days). Pick a class chip to load its typical duration, then read the same frost-margin check.
What is the FAO maize maturity number?+
The FAO maturity number classifies maize hybrids by relative maturity: FAO 100–200 are very early (about 80–95 days), FAO 300 early, FAO 400–500 medium, and FAO 600–700 late (about 125–145 days). Higher numbers need a longer, warmer season. Match the number to your frost-free days the same way you match a soybean MG to your latitude.
Why does maturity group change with latitude?+
Soybean flowering is triggered by night length, which changes with latitude and date. A variety bred for long northern days will flower and mature too quickly if moved south, and a southern variety will keep growing vegetatively too long if moved north. The maturity-group adaptation map encodes this so each band gets a variety whose photoperiod response fits its day-length and season.
What if my margin is tight?+
A tight margin (0–7 days) means the variety only just ripens before an average first frost — a slightly early frost or a cool, slow finish could catch it. Either drop to a shorter-duration variety (an earlier maturity group), bring the sowing date forward, or accept the risk knowingly. The tool shows the longest duration that still fits your corridor with the buffer intact.
Do I use absolute latitude for the southern hemisphere?+
Yes — enter the absolute value. Soybean maturity-group adaptation mirrors across the equator, so 33°S behaves like 33°N for variety choice. The frost dates you enter handle the calendar difference (a southern-hemisphere season runs October–April), so the margin still comes out correct.
How accurate are the frost-free days?+
First-frost dates are long-term averages; any single year can frost two or three weeks early or late. Use a local 50% or 10% frost-probability date from your meteorological service for the date you enter, and keep the 7-day buffer. Treat the margin as a planning figure, not a guarantee — that is exactly why the buffer exists.
Where do these maturity bands come from?+
The soybean MG-by-latitude bands follow the standard USDA and university-extension soybean maturity-group adaptation maps (used by Nebraska, Iowa State, OMAFRA and others). The rice, wheat and maize duration classes follow ICAR varietal duration tables and the FAO maize maturity classification. They are planning references; your local seed catalogue gives the exact days for a named variety.