Wyoming turnip growers get two sowing windows: spring, starting when the soil can be worked, and midsummer for a fall crop. Both hang on a short season. The frost-free stretch runs roughly 130 days at 6,000 feet, and at higher elevations frost can arrive in any month. That leaves a quick crop like turnips some room to work and squeezes slow rutabaga hard.
The short answer for Wyoming
Sow turnips outdoors as soon as the soil is workable in spring, which means ahead of or during the last-frost band of May 7 to May 18. Sow again in midsummer, counting back from a first fall frost that falls between September 24 and October 5.
Those dates need a careful reading. They come from the NOAA 1991-2020 Climate Normals for one reference station, and each is a probability, not a deadline. The band marks where the chance of a 32°F freeze sits between 30 and 70 percent. On May 7 a freeze is still close to a coin flip, and even after May 18 it has not dropped to zero. The fall dates work the same way in reverse: by September 24 a first freeze is already a real possibility, and by October 5 it is more likely than not. The underlying NOAA station data is public if you want to check it.
Turnips are a cool-season root that tolerates light frost, so the spring band is not a wall. Seed can go in before it, and seedlings can handle a mild dip, though a hard freeze can still knock back young plants. The fall band matters more. A midsummer sowing has to size up before the soil chills, which is why the planting date is worked backward from the early end of the fall range.
| Sowing | Anchor in the frost facts | Practical window |
|---|---|---|
| Spring | Last 32°F freeze band, May 7 to May 18 | Soil workable, ahead of or during the band |
| Fall | First 32°F freeze band, September 24 to October 5 | Midsummer, counted back from September 24 |
The page does not have a Wyoming extension turnip calendar to check these windows against, so treat them as a starting frame built from the frost dates alone. For the varieties that fit them, see The Best Turnips and Rutabaga for Wyoming.
What will not work here
Slow rutabaga sown late is the first casualty. From the end of the last-frost band on May 18 to the start of the first-frost band on September 24, the calendar offers roughly 130 frost-free days at 6,000 feet. A long-season rutabaga that needs most of that, sown in June or after, will be racing a freeze it cannot beat. Higher up, where frost can show in any month, the margin disappears.
Waiting for warm soil backfires too. A gardener who holds seed until late May, the way tomato growers do, pushes the crop into the hottest stretch of summer. Turnips grown through heat tend to turn woody and sharp. Cool weather at both ends of the season is the whole reason to sow early and again late.
Trusting a single date fails as well. Writing “last frost May 18” on the calendar treats a 30 to 70 percent band as a guarantee. Seedlings set out with no cover on May 19 are still gambling, and in a high-elevation yard the gamble is worse. Keep row cover or a cloth on hand through the end of the band, and some years beyond it.
Watering once a week does not suit a root crop in a dry, windy climate. Turnips want steady moisture while the root swells. A deep soak followed by days of drying wind gives you split, bitter, or woody roots. Small, frequent waterings (and a mulch once seedlings are up) do better than a weekly flood.
Counting on winter storage in the ground is the last mistake. The coldest month here has a mean daily minimum of 18.1°F at the Cheyenne reference station, and that is an average, not the extreme. Turnips and rutabaga are not left in the bed to overwinter in Wyoming. Pull them before the ground freezes hard, and store them cool.
Finally, seed packets that say “sow eight weeks before first fall frost” assume you know that frost date. In Wyoming you know a band, so count from the early end, September 24, and subtract more time if you are above 6,000 feet.
What changes across Wyoming
There is no single answer for the state. The USDA Plant Hardiness Zone Map (2023, built on 1991-2020 normals) puts Wyoming at 3a to 6a, a spread of three full zones. That is the gap between a garden where winter lows can be brutal and one that sits in much milder country.
Keep in mind what the zone measures. It rests on one variable, the average annual extreme minimum temperature. That tells you whether a perennial survives the winter. Turnips are annuals and come out before the deep cold, so the zone number says little about when to sow them. Frost dates and elevation matter far more, and the dates on this page are anchored to one reference station at roughly 6,000 feet.
Readers in the north or at altitude should shift in the same direction. Spring sowing slides later because the soil stays cold longer. Fall sowing slides earlier, since the first freeze arrives sooner and, in high country, may arrive in any month. In the coldest and highest gardens the two-crop plan can shrink to one: a spring sowing under cover, or a single early-summer sowing, with fast turnips only. Rutabaga becomes a risk you take on purpose, not a default.
Readers in the milder southeast corner and lower valleys may find the spring window opens earlier and the fall one stays open longer. Do not guess which group you belong to. Look up your own spot on the USDA Plant Hardiness Zone Map and compare it with the range above, remembering that a zone gives winter cold, not a sowing date.
Where to check this for your own county
Your state extension service is the next stop. University of Wyoming Extension runs the land-grant outreach program, with county offices across the state. Two things are worth looking for there: the local planting calendar for your area, and the varieties that have actually been trialled in your county.
The first tells you how your county’s frost dates and soil warm-up differ from the reference station used here. The second matters more for rutabaga and for slower turnips. A variety that looks fine on paper may never have been tested at your elevation, and county trial notes will say which ones finished before the freeze.
A county recommendation beats a state one. This page is the state one: a frame built from one set of frost normals, a hardiness range, and general behavior of the crop. It can tell you the shape of the season, but not whether your valley holds cold air or your hillside warms a week early. If the extension office gives a date that disagrees with the one here, trust the office.
While you are checking, ask whether the office has a turnip or root-crop sheet specific to your area. For the broader picture, Growing Turnips and Rutabaga in Wyoming covers the crop from seed to harvest.
Checking this against your own garden
Your own observations outrank every date above, and three of them cost nothing.
The first is soil warmth by feel. Push a bare hand a few inches into the bed in the morning. If it feels raw and cold, seed will sit and may rot, so wait. If it crumbles and feels cool rather than icy, you can sow. A bed that reaches that point a week before your neighbor’s is telling you it has sun, shelter, or good drainage.
The second is the first flush of male flowers. Watch the catkins on the cottonwoods or willows near you, or the first male blooms on whatever plant you track from year to year. Note the date. A tree that opens early in your yard says your spot warms ahead of the average. Keep that log across a few seasons and it becomes your own calendar.
The third is the first true leaves on a test row. Sow a short row early, and when the seed leaves are followed by the rough, rounder true leaves, you know that spot supports growth. Stalled, yellow, or purple seedlings point to a cold pocket, and a frost-prone low spot will show itself the same way.
Some gardeners also time this by the Moon: when to plant turnips by the moon, as almanac tradition rather than fact.
Common questions
Can I sow turnips in Wyoming before the last frost?
Yes. Turnips tolerate light frost, so seed can go in once the soil is workable, ahead of the May 7 to May 18 band. Keep a cover ready for a hard freeze, because a young seedling is less forgiving than an established plant.
Can I get two turnip crops in one year?
In many Wyoming gardens, yes: one spring sowing and one midsummer sowing for fall. Above 6,000 feet, where frost can arrive in any month, a single crop may be the realistic plan.
Does my hardiness zone tell me when to sow?
No. The USDA zone rests on the average annual extreme minimum temperature, which measures winter survival. For turnips, frost dates and elevation set the calendar. Use the zone map to see where you sit in the 3a to 6a spread, then lean on frost dates.
When is it too late to sow turnips for fall?
Check the days to maturity on your seed packet and count back from September 24, the early end of the first-frost band. Slower rutabaga needs an earlier start than turnips. At higher elevations, subtract more time, because the first freeze can arrive sooner than the reference station suggests.