Growing Unusual Root Crops in North Dakota

In North Dakota, plant or sow these roots after the last spring freeze has passed and the soil has warmed, not on a fixed calendar date. At the Fargo reference station that freeze falls between May 4 and May 15, and the first fall frost arrives September 25 to October 5. Most of the group fits that window. Celeriac is the one to watch, and Jerusalem artichoke is the one to site carefully.

When the soil is warm enough in North Dakota

Reading the frost dates

NOAA’s 1991-2020 U.S. Climate Normals put the last spring 32°F freeze at Fargo between May 4 and May 15. That range is the 30-70% probability band, so it is a probability, not a promise. A freeze after those dates is always possible. The figures also come from an airport weather station. Suburban and rural gardens usually see the last spring frost later, often by one to two weeks, so check your own county before you mark a calendar.

Frost is only a proxy here. Celeriac, kohlrabi, horseradish and the rest are waiting on warm soil, and soil warms after the frost risk ends, not at the same moment. Seed in cold ground sits and rots. A celeriac transplant set into chilled soil stalls, and a cold snap can push it toward flowering instead of building a root. A basic soil thermometer pushed in at planting depth on a spring morning tells you more than the last-frost date does. The hardy types, kohlrabi and turnip among them, tolerate cooler ground than celeriac, so they can go in first.

Varieties are another matter. This page names none, because it has no North Dakota trial data to back a name. North Dakota State University Extension publishes what has actually been trialled in the state, and that list beats any recommendation from a seed catalog written for the whole country.

Site Jerusalem artichokes before you plant them

Settle the location first, because this is the planting gardeners most often regret. Jerusalem artichoke is effectively permanent once it is in the ground. Every fragment of tuber left behind regrows, and a single missed piece the size of a thumb becomes a new clump. Give it a corner you will never want for anything else, bounded by a mowed strip, a driveway edge or a solid barrier, and well away from the vegetable beds. A stand left to spread through a rotation bed cannot be rotated out.

Once the site is chosen, planting is simple. Set tuber pieces in spring when the soil can be worked. The plants are tall, so put them where they will not shade anything. As a plain fact of the vegetable, the tubers store inulin rather than starch, and many people get digestive discomfort from them. Start with a small first portion and see how you do.

Horseradish is the other perennial in the group and behaves in much the same way. Root pieces left in the soil regrow, so give it its own bed too.

How long the season lasts here

Count from the latest spring date to the earliest fall date and the Fargo window is 133 days, May 15 to September 25. From the earliest spring date to the latest fall date it is 154 days, May 4 to October 5. Both come from the same NOAA normals, so the subtraction is sound for the reference station. A garden outside Fargo may lose a week or two at each end, and the short case then falls well below 133 days. A garden at higher elevation or in an open rural spot loses more.

What does a window like that allow? For the quick types, kohlrabi and turnip especially, a Fargo-length season leaves room for two sowings: one in spring and a later one timed to mature in the cooler weeks of fall. At the short end of the range, treat the second sowing as a bonus, not a plan. The succession sowing guide on this site covers the spacing between sowings and how to count back from your own first fall frost.

Slow roots get one shot. Celeriac and parsnip, the long-season members of the group, have a single sowing and the window either holds or it does not. For celeriac that makes transplanting worth the trouble, since starting seed indoors well ahead of the last frost buys weeks that the outdoor season cannot spare. The risk is the roots. Celeriac seedlings handle transplanting if the root ball stays intact and the plants are hardened off before they meet wind and cold nights. Taprooted crops like parsnip and turnip do better sown where they will grow, and a damaged taproot comes up forked.

The fall end of the window is softer than it looks. A first 32°F freeze does not end the harvest for the hardy roots, which keep sizing up through cool weather, and many gardeners treat the first frost as the signal to start mulching, not to start digging. Frost-tender companions in the bed are another matter, so check your own forecast before leaving anything exposed overnight.

For the broader picture of these crops, see Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes. This page narrows it to North Dakota’s clock.

Heat and water in North Dakota

The verified facts behind this page do not include a count of days above 90°F or a summer rainfall total, so none is quoted here. Any such count would be a reading at one reference station, not a description of a whole state, and your county Extension office can give you figures for where you actually garden. What this page can say honestly is that two facts do most of the governing for this group: season length and winter low. Heat is secondary, and this is not a territory to write a hot-climate watering routine for.

Season length decides whether celeriac can finish at all. With 133 to 154 days at Fargo, and fewer in many rural gardens, the margin is thin for the longest crop in the group. A cool, damp summer makes it thinner, and what that brings is mildew, slow ripening and disease pressure, not heat stress. A hot, dry stretch is a different problem: uneven watering splits roots and makes kohlrabi woody. A layer of mulch evens out the swings in both directions.

Wet years also raise a point about disease. Turnip and rutabaga are brassicas, and so are kohlrabi and horseradish. They share their troubles with cabbage, kale and mustard. A gardener who rotates turnips into a bed that held cabbage has rotated nothing. The crop rotation guide on this site explains how to count families, not individual crops.

The winter low sets the overwintering plan

At Fargo, the mean daily minimum of the coldest month is 0.2°F (NOAA 1991-2020 Climate Normals). The USDA Plant Hardiness Zone Map of 2023 places North Dakota in zones 3a to 4b. That system is built on a single variable, the average annual extreme minimum temperature. The range covers the whole state, so other parts will differ from Fargo.

That cold shapes the choice between leaving roots in the ground and lifting them. Horseradish and Jerusalem artichokes are perennials that overwinter under mulch. Hardy roots like parsnip can stay too, as long as a deep mulch keeps the soil from locking solid, because frozen ground is nearly impossible to dig. Celeriac does not belong in that group. Lift it, along with any tender roots, before the soil freezes.

Lifted roots need inspection, not trust. Check each one for a soft patch, a weeping spot or a moldy crown, and any of those ends the question: the root goes in the compost, not on the plate. Never assume a root is safe because it looks sound on the outside. This page promises no keeping duration, because none can be promised.

If you prepare horseradish, know that grating a fresh root releases compounds that burn the eyes and airways. Work with good ventilation, keep your face well away from the bowl, and open the grater outdoors or near an open window.

Which these root crops suit North Dakota

Choose by type first. A short season favors the earliest types, which means quick kohlrabi and turnip over the slow roots. For celeriac, it means picking the earliest-maturing type available and starting it indoors. A hot season, where you get one, favors types given airflow and shade at the root. A damp or humid one makes disease resistance the first criterion on the seed packet, ahead of flavor or size.

No variety is named on this page, and that is deliberate. Naming a cultivar means pointing to trial results from North Dakota growing conditions, and this page does not have them. A variety that performs in a catalog photo may sulk in Fargo clay or in a western county with different frost dates. NDSU Extension and its county offices know which ones have been grown and tested locally, and that is the only recommendation worth acting on.

Gardeners in milder places grow the same crops on a different clock. For comparison, see Growing Unusual Root Crops in Washington and Growing Unusual Root Crops in California.

Common questions

Can I plant these roots as soon as May 4 passes?

Not by the date alone. May 4 to May 15 is the Fargo range for the last 32°F freeze, and rural gardens usually run one to two weeks later. Soil warms after the frost risk ends, so check the soil itself and your county’s dates.

Will Jerusalem artichokes survive a North Dakota winter?

They are a hardy perennial and are generally left in the ground under mulch. The same trait makes them permanent: any tuber fragment left in the soil regrows, so choose the site carefully.

Is celeriac worth trying with a season this short?

It is the long crop in the group, and the Fargo window runs 133 to 154 days, less in many rural gardens. Transplants started indoors give it the best chance. Ask NDSU Extension about types trialled in your area.

Can I plant turnips or rutabagas where cabbage grew last year?

No. Turnip and rutabaga are brassicas and share their pests and diseases with cabbage, kale and mustard. Move them to a bed that has been free of the whole family.