In Charlotte, the last spring freeze falls between March 23 and April 5, and most unusual roots should wait until the soil, not just the air, has warmed past that window. Celeriac, kohlrabi, horseradish and Jerusalem artichokes can all work in North Carolina. But the mountains, the Piedmont and the coast run on different calendars, so treat the dates below as a starting point. The full crop-by-crop guide is here: Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes.
When the soil is warm enough in North Carolina
Start with the date everyone asks about. The NOAA NCEI U.S. Climate Normals 1991-2020 for the Charlotte station put the last spring 32°F freeze between March 23 and April 5. That is the 30-70% probability band. A frost date is a probability, not a promise, and some years a cold night will land after the later date.
Frost is only a proxy. Roots do not care what the air did at 6 a.m.; they respond to soil temperature. Ground holds winter cold long after the nights stop dipping below freezing, so the soil warms after the frost risk ends, not with it. A cheap soil thermometer pushed a few inches down in the morning tells you more than the calendar does. Your extension office can give you the minimum soil temperature for each crop.
Location shifts everything. Charlotte is Piedmont. The Blue Ridge to the west runs several weeks later in spring, and the coastal plain runs earlier. The USDA Plant Hardiness Zone Map 2023 spans 5b to 8b across the state, so the Charlotte figures are a reference point, not a statewide rule.
What waits and what does not
Kohlrabi is the outlier. It tolerates cool soil, so it goes in first in spring and again in late summer for a fall crop. It is also a brassica, like turnip and rutabaga, which means it shares its pests and diseases with cabbage, kale and mustard. Rotating it into a cabbage bed rotates nothing, so check the rotation page on this site before you plan the bed.
Celeriac is the opposite case. Its transplants wait until the frost risk has ended, and a cold snap after planting can set them back. Horseradish and Jerusalem artichokes go in once the ground is workable and warming.
Site Jerusalem artichokes before you plant them
Read this part first. Jerusalem artichoke is effectively permanent once planted. Every fragment of tuber left in the ground regrows, and digging the patch up only scatters more pieces. It is the single most regretted planting in many vegetable gardens. Give it a corner you are willing to surrender, or a bed bordered by lawn or pavement that you can mow or patrol. Never put it in the middle of your rotation.
Horseradish behaves similarly, since root pieces left behind can resprout. When you prepare it, remember that grating a fresh root releases compounds that burn the eyes and airways. Ventilate the kitchen and keep your face well away from the bowl. As for Jerusalem artichokes at the table, they store inulin instead of starch, and many people find that causes digestive discomfort. A small first portion is the sensible way to find out. Do not count on cooking or frost to remove it.
How long the season lasts here
Both frost dates come from the same Charlotte station file. The first fall 32°F freeze falls between October 30 and November 8, again in the 30-70% band. Count from the latest spring date (April 5) to the earliest fall date (October 30) and you get 208 days. Count from the earliest spring date (March 23) to the latest fall date (November 8) and you get 230. So the frost-free span at Charlotte runs from roughly 208 to 230 days, depending on which end of each band the year hands you.
That number is the air’s calendar, not the roots’. The soil lag trims the front end, and the crop’s own maturity period (printed on the seed packet or plant tag) has to fit inside what is left.
What does that length allow? A second sowing, mainly. Kohlrabi can be sown in spring and again in late summer, with the fall sowing timed backward from the October 30 to November 8 freeze window using the packet’s maturity figure. Horseradish and Jerusalem artichokes do not need a second sowing, since they sit in the ground for the whole season.
The window also changes the transplanting question. In a short season you transplant to gain weeks and accept the stress on the roots. Here there is room to direct-sow the roots that resent being moved and save transplants for celeriac, whose slow seed is the real reason to start indoors. The succession sowing guide on this site covers how to stagger plantings so the harvest does not arrive all at once.
Elevation changes the math. In the mountains, where spring comes several weeks later, the window is shorter. There the first sowing may be the only one, and transplanting becomes more attractive because it buys back weeks. On the coastal plain, spring comes earlier and the window stretches. This page does not have verified frost dates for those regions, so use your local extension office rather than guessing.
Heat and water in North Carolina
The verified facts behind this page do not include a count of days above 90°F or a summer rainfall total, so I will not quote either. The Charlotte station file and your extension office carry them. What can be said honestly is that Piedmont summers are hot and humid, and two other facts govern this group of crops far more than any single summer statistic.
The first is season length, and it matters most for celeriac, the long one. A 208 to 230 day frost-free window looks generous on paper. But celeriac has to finish before the fall freeze, and the middle of its growth sits in summer heat. Heat stalls it, and uneven watering is a known cause of cracked or hollow roots. Mulch keeps the root zone cooler and the moisture steadier. Spacing for airflow helps against the foliage diseases that humid weather encourages, and so does watering at the base of the plant in the morning rather than overhead in the evening.
The second is the winter low. The coldest month at Charlotte has a mean daily minimum of 31.8°F (NOAA NCEI Climate Normals 1991-2020). That is an average of the nightly lows, not the record low, so individual cold snaps go well below it. Still, an average night barely under freezing means horseradish and Jerusalem artichokes, both perennials, can stay in the ground under a layer of mulch at Charlotte-like sites. Celeriac and kohlrabi are not perennials, and a hard freeze damages them, so harvest them before the ground freezes.
In the mountains, where the hardiness map drops toward 5b, the ground freezes harder and the sensible choice shifts toward lifting and storing before the soil freezes. Stored roots deserve a close look before use. Check them for firmness and dryness. A soft patch, a weeping spot or a moldy crown ends the question, and that root goes to the compost, whatever the rest of it looks like. A root that looks sound is not thereby safe, and no keeping time can be promised.
Which these root crops suit North Carolina
Choose by type, not by cultivar. The state’s conditions point to three criteria. The generous Piedmont season favors getting two kohlrabi sowings. Summer heat favors types that get airflow and shade at the root. And humidity makes disease resistance the first thing to look for on a label.
| Type | Fit in North Carolina | What to look for |
|---|---|---|
| Kohlrabi | Spring and fall sowings both fit the window | Early types for spring; disease resistance (it is a brassica) |
| Celeriac | Needs the whole season; heat is the risk | Resistance to leaf disease; mulch and steady water |
| Horseradish | Perennial; sits through summer and winter | A contained site; ventilation when grating |
| Jerusalem artichoke | Very tolerant; permanent once planted | A site you can give up for good |
This page names no varieties, and that is deliberate. The only recommendation that means anything is the one tested where you garden, in your soil and your humidity. Cultivars that thrive in a trial in the Piedmont may sulk in the mountains or on the coast. This page does not have those trial results, and a variety name pulled from memory is how gardeners end up with a failed row. North Carolina State Extension and your county office can tell you which varieties have been trialled near you.
If you want to see how the same crops fare in other climates, compare this page with Growing Unusual Root Crops in Oklahoma and Growing Unusual Root Crops in British Columbia. The contrast makes clear how much the choice of type depends on season length and humidity.
Common questions
Can I plant before April 5?
Kohlrabi, yes, since it tolerates cool soil. For the rest, the later end of the frost band is a sensible marker, and the soil thermometer is a better one. An early start in a warm spell risks losing young plants to a late cold night, since the frost date is a probability, not a guarantee.
Do Jerusalem artichokes upset your stomach?
Many people find they do, because the tubers store inulin rather than starch. Start with a small first portion and see how you react. Cooking is not a promise of relief, and neither is waiting for frost.
Can horseradish stay in the ground over winter?
It is a perennial, and at Charlotte, where the coldest month averages a 31.8°F nightly minimum, it can overwinter under mulch. Colder mountain sites may call for more protection. When you do harvest it, grate it in a ventilated room with your face well back, because the vapors burn eyes and airways.
Do Charlotte’s dates apply across North Carolina?
Only roughly. The Blue Ridge runs several weeks later in spring and the coastal plain earlier. The USDA 2023 hardiness map spans 5b to 8b across the state, and it is built on a single variable, the average annual extreme minimum temperature. It tells you what winter will do to a perennial, but nothing about frost dates or summer heat.