When to Sow Turnips in Wisconsin

Sow turnips in Wisconsin twice: in spring around the last freeze, April 16 to April 29, and again in late summer so the roots finish before the first fall freeze, October 17 to October 29. Both ranges are probabilities, not guarantees. Rutabaga runs on a slower calendar of its own. The sections below show how to count back from those dates.

The short answer for Wisconsin

Those two ranges come from the NOAA NCEI 1991-2020 Climate Normals, and they are probabilities of a 32°F freeze. The spring range, April 16 to April 29, is the stretch where the odds of another freeze fade through the 30 to 70 percent band. The fall range, October 17 to October 29, is the same band on the way back up. Neither is a date on which frost stops or starts. A freeze can still show up after the later spring date, and it can arrive before the earlier fall one.

Turnips are a cool-season root that shrugs off light frost, so you do not need to wait for the spring band to close. Sow as soon as the soil is workable and no longer sodden, with the band as your reference point rather than a gate. The real limit comes at the other end. Roots sown in spring have to size up before summer heat arrives, and that is why the fall sowing often gives the better crop.

How to count the fall sowing

Work backward. Find the days to maturity on your seed packet, subtract that number from October 17, and add a cushion for the slower growth of short autumn days. That gives your latest sowing date. Using the earlier end of the range is the cautious choice, because the band describes odds and not a promise. A light freeze does not hurt turnips, and many gardeners find the roots taste sweeter after one. A hard freeze is what ends the harvest.

Rutabaga needs far more time than turnips, so it cannot follow the quick fall schedule. Sow it in early summer and treat the first freeze band as its deadline. For the varieties that suit this calendar, see The Best Turnips and Rutabaga for Wisconsin.

What will not work here

Sowing rutabaga in late summer fails. The first fall freeze band opens October 17, and in the north and inland it can arrive earlier, so a long-season root planted in August simply runs out of days. You get leaves and a small, stunted root. The same applies to any slow turnip variety pushed into the fall slot. Short-season types belong there.

Waiting until late spring fails too. Turnips sown in May mature into the heat of midsummer, and hot weather pushes them toward woody, bitter, or bolting roots. The spring crop is a race against summer, which is why early sowing matters and why the fall crop tends to be more forgiving. If you only get one good sowing, make it the one that finishes in cool weather.

Leaving roots in the ground to overwinter fails as well. The mean daily minimum of the coldest month is 17.2°F (NOAA NCEI Climate Normals 1991-2020, Milwaukee reference), and that is an average, not the extreme low. Soil freezes hard under those conditions, so roots left in the garden turn to mush rather than keep. Harvest before the ground locks up, and store them cool and damp. Winter hardiness is not what decides success with turnips, since they are grown as an annual. It matters only as the reason the harvest deadline is firm.

Counting on the lake for extra time also backfires. Lake Michigan delays the first fall freeze at the lakeshore, but inland southern Wisconsin typically freezes in early October, and the north far earlier. A gardener who trusts the October 17 to October 29 range a few counties from the lake may lose a fall crop weeks ahead of schedule. Use the range as a starting guess, then check it against what your own garden does.

Finally, thick sowing in a humid stretch invites trouble. Crowded turnip tops stay wet and shaded, which favors leaf disease, and thinning to proper spacing is not optional. Cool, damp weather also tends to favor the pests that hit brassicas in spring, so row cover is a reasonable precaution early in the season.

What changes across Wisconsin

There is no single Wisconsin answer. The USDA Plant Hardiness Zone Map (2023, built on 1991-2020 normals) places the state in zones 3b through 6a. That is a spread of several zones, and the system measures one thing only: the average annual extreme minimum temperature. It tells you about winter cold, not the length of your growing season, so it is a rough guide for a quick annual like turnips. The frost dates matter more for this crop.

The dates on this page come from a single NOAA station and describe the southern part of the state. Do not stretch them statewide. Northern Wisconsin sits in the colder end of that range and its first fall freeze comes far earlier. A northern gardener should plan the fall sowing earlier, favor the fastest varieties, and drop rutabaga from the late schedule altogether, sowing it as early in summer as the soil allows. Higher or lower ground inside the same county can also shift your own freeze dates, since cold air pools in low spots.

Lakeshore gardeners get the opposite shift. Lake Michigan delays the first fall freeze, which gives a fall turnip crop extra time to finish. The same lake keeps spring cool, so the soil there can warm more slowly. Which hardiness zone you sit in depends on where your garden is, so check the USDA Plant Hardiness Zone Map rather than guessing from a county name. For a wider look at the crops themselves, start with Growing Turnips and Rutabaga in Wisconsin.

Where to check this for your own county

Your state extension service is the next stop. University of Wisconsin-Madison Extension runs offices in counties across the state, and its staff know local frost patterns, soil types, and pest pressure in a way a statewide page cannot. A county recommendation beats a state one, and this page is the state one.

When you get there, look for two things. The first is a local planting calendar for root crops or cool-season vegetables, ideally one tied to your county or nearest region. The second is any record of varieties trialled in your area, because a turnip that performs in the south may not mature before frost in the north. If you can reach your county office, ask which fall sowing dates local gardeners are using and whether rutabaga is reliable in your part of the state.

This page does not have a Wisconsin turnip calendar published by extension to quote, so the dates above rest on the NOAA frost probabilities alone. Treat any extension calendar you find as the more local authority, and treat the numbers here as a framework to compare it against. Extension publications are often written per crop, so use the one for turnips or rutabaga, not a neighboring vegetable.

Checking this against your own garden

Your own observations outrank every date on this page. Three are easy to watch without any equipment.

• Soil warmth by feel. Dig a handful a few inches down in the morning. If it crumbles and feels cool rather than cold and clammy, it is ready for spring turnip seed. Soil that stays cold long after your neighbors’ gardens thaw points to a shaded, low, or heavy spot, and you should sow later there.
• The first flush of male flowers. Squash or cucumber plants in a nearby bed start with male flowers before female ones. Where those open early, your garden runs warm, which warns you that spring turnips will meet summer heat sooner.
• The first true leaves. Turnip seedlings show two round seed leaves first, then the first true leaves. Slow, pale growth at that stage suggests cold soil or poor drainage. Fast, sturdy growth tells you the bed suits the schedule.

Jot down the dates you see these signs each year. After two or three seasons, your notes will describe your garden better than any statewide range.

The Moon calendar is a separate, older custom: see when to plant turnips by the moon, written as tradition rather than fact.

Common questions

Can I sow turnips before the last spring freeze?

Yes. Turnips tolerate light frost, so sowing in the weeks around the April 16 to April 29 band is normal as long as the soil is workable. A hard freeze can still damage tender seedlings, so cover them if a cold snap is forecast.

When is the latest I can sow turnips for fall?

Count back from the first fall freeze band, October 17 to October 29, using the days to maturity on your packet, then add a cushion. In the north and inland, start from an earlier date, because frost arrives sooner there.

Can I grow rutabaga as a fall crop sown in late summer?

It is a poor bet. Rutabaga needs a long season, so sow it in early summer and plan for the first freeze band as its deadline. Late sowing usually gives a small root.

Do the zones 3b to 6a tell me when to plant?

Not by themselves. The USDA zone reflects average annual extreme minimum temperature, which speaks to winter cold. For sowing dates, use frost probabilities and your county extension guidance.