In Kentucky, the planting date for unusual roots comes from the soil, not the calendar. At the Louisville station, the last spring freeze falls between March 24 and April 4, and that is only the earliest point at which anything can start. Celeriac, kohlrabi, horseradish and Jerusalem artichokes each read the season differently, and the state’s winter low settles the rest. For the full crop profiles, see Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes.
When the soil is warm enough in Kentucky
NOAA’s 1991-2020 Climate Normals for the Louisville station put the last spring 32 F freeze between March 24 and April 4. That range is the 30 to 70 percent probability band, so it describes odds, not a promise, and a late freeze after the band is possible. The source data is the NOAA NCEI normals file.
One caution comes with it. The National Weather Service in Louisville warns that this urban station runs later in spring and earlier in fall than the rural parts of Jefferson County around it. A garden out in the country should expect a tighter window than the city numbers suggest.
Frost is a stand-in. These crops wait for warm soil, and soil lags the air. It warms after the frost risk ends, not at the same moment. A soil thermometer at planting depth tells you more than any date. A bed that is still cold and sodden in early April will rot seed and stall transplants, however mild the afternoons feel.
The group splits by temperament. Kohlrabi and the turnip-and-rutabaga crowd tolerate cool soil and can go in as soon as the bed is workable. Celeriac is the opposite: it goes out as a transplant after frost risk has passed, because a chilled seedling can bolt instead of swelling. Horseradish and Jerusalem artichoke pieces go in once the ground can be dug without clumping.
Varieties are another matter. Which ones perform in Kentucky soils is a question for the University of Kentucky Cooperative Extension Service, which knows what has been trialled in your county. This page does not name any.
Site Jerusalem artichokes before you plant them
Decide where Jerusalem artichokes go before you read how to grow them, because once planted they are effectively permanent. Every fragment of tuber left in the soil regrows. Digging the bed over, however carefully, just sows the leftovers. Gardeners regret this planting more often than any other in the vegetable garden.
Give them a bed you will never want for anything else: a back corner, a strip bounded by lawn you mow or by a hard edge, or a large container sunk where it cannot tip. Plan to dig every tuber each year, accept that some will escape, and keep them well away from beds you intend to rotate.
These tubers store inulin rather than starch, and many people get digestive discomfort from eating them. That is a plain fact of the vegetable. A small first portion is the sensible way to find out how you react.
How long the season lasts here
Both frost dates for Louisville come from the same NOAA normals. The first fall freeze falls between November 2 and November 12. Counting from the latest spring date (April 4) to the earliest fall one (November 2) gives 212 days. Counting from the earliest spring date (March 24) to the latest fall one (November 12) gives 233. The window runs roughly 212 to 233 days, a little over seven months at the short end. For rural gardens, assume the lower end or less, per the NWS caution above.
The length matters for what it allows. A window this long permits a second sowing. Kohlrabi, turnips and rutabagas can go in once in spring and again in late summer, so that the second crop matures in the cooler weeks before the November freezes. Rutabaga and turnip in particular do better when their roots swell in cool conditions, which makes the fall sowing the more natural one. The succession sowing guide on this site lays out how to stagger those plantings.
It also changes the transplant calculation. Celeriac is the long-season crop of the group, and the main reason to start it indoors is to use the early part of the season it would otherwise waste. With seven-plus months available, the setback from a root-disturbing transplant can be absorbed, so long as you handle the root ball gently and harden the seedlings off. Turnips, rutabagas and kohlrabi are another story, since disturbed roots tend to fork or stall. Sow those where they will grow.
Season length is the first thing that separates states. The same crops sit on a very different calendar in the mountains of Growing Unusual Root Crops in West Virginia or along the coast in Growing Unusual Root Crops in Rhode Island, so do not carry dates across a state line.
Heat and water in Kentucky
The verified figures for this page do not include a count of days above 90 F or a summer rainfall total, so none are quoted here. Inventing a number for the Louisville station would only mislead, and the count describes one reference station anyway, not the whole state. For heat and rainfall in your own county, check local weather records or ask the extension service.
Two things the figures do establish govern this group. The first is season length, which says celeriac can finish here at all. At 212 to 233 days between freezes, the calendar is generous enough. What can stop it is a summer that stresses the plant before the swelling starts. Celeriac wants steady moisture and cool roots, and a thick mulch plus consistent watering through dry spells protects both. Kohlrabi gets woody and tough when it matures in heat, which is one more reason to favor the fall sowing.
The second is the winter low. At the Louisville reference station, the mean daily minimum of the coldest month is 27.8 F, per NOAA’s 1991-2020 normals. That is an average, not the record low. The USDA Plant Hardiness Zone Map (2023) puts Kentucky at 6a to 7a. That system rests on a single variable, the average annual extreme minimum, and it is a range, so parts of the state differ from Louisville.
For the perennials, the verdict is generous. Horseradish and Jerusalem artichokes are hardy enough to winter in the ground in these zones, so leaving them under a layer of mulch is reasonable. Hardy roots such as rutabaga and turnips can usually stay in the soil under mulch too, as long as you pull them before the soil freezes hard. Celeriac is the one to lift, because it is the least tolerant of a hard freeze in the group.
Anything you lift and store needs inspecting, not trusting. Look at every root before it goes into storage and again as you use it. A soft patch, a weeping spot or a moldy crown ends the question: that root goes in the compost, not on the plate. A root that looks sound is not thereby safe, and no storage duration is promised here.
Horseradish asks for care in the kitchen. Grating fresh root releases compounds that burn the eyes and airways. Ventilate the room, keep your face away from the bowl, and do not treat it as a joke.
Which these root crops suit Kentucky
Choose by type, and let the state’s conditions set the criteria. A season of 212 to 233 days between freezes is long, so there is no need to hunt for the very earliest types. What matters more is how a type copes with a warm, humid stretch in summer, which makes airflow, root shade and disease resistance the deciding factors.
| Crop type | What Kentucky conditions favor |
|---|---|
| Celeriac | Transplants started indoors, mulched roots, steady watering through summer |
| Kohlrabi | A spring sowing plus a late-summer one, with the fall crop usually easier |
| Turnip and rutabaga | Fall-maturing sowings; both are brassicas |
| Horseradish | Dug and divided in a dedicated bed; hardy under mulch |
| Jerusalem artichoke | A permanent, contained site; hardy through winter |
Turnip and rutabaga are brassicas. They share their pests and diseases with cabbage, kale and mustard, and a gardener who rotates them into a cabbage bed has rotated nothing. Give them a bed that has been free of the whole family, as described in the crop rotation guide on this site. In a humid climate, disease resistance should be the first thing you look for in any type of brassica root.
This page names no variety, and that is deliberate. The only variety advice worth following is what has been trialled in Kentucky itself, and this page does not have those results. A name copied from a seed catalog or another state’s list is a guess dressed up as a recommendation. The University of Kentucky Cooperative Extension Service and its county offices know what has grown well locally, and they can tell you about pest and disease trouble in your area.
Common questions
Is the last frost date the day to plant?
No. For Louisville the last spring freeze falls between March 24 and April 4, but that is a probability band, and these roots respond to soil temperature, which warms after the frost risk ends. Cool-season crops can go in once the soil is workable. Celeriac waits longer.
Can celeriac finish in Kentucky?
The window between freezes is roughly 212 to 233 days, which is long enough on paper. Summer stress is the real risk. Mulch, steady water and a transplant started indoors give it the best chance.
Can I leave Jerusalem artichokes and horseradish in the ground over winter?
In USDA zones 6a to 7a, both are hardy enough to winter in the soil under mulch. Jerusalem artichoke regrows from any tuber left behind, so site it where that will not matter. Check the zone for your specific location, since parts of the state differ from Louisville.
Can I plant turnips or rutabagas where cabbage grew?
Not if you want a real rotation. They are brassicas and share pests and diseases with cabbage, kale and mustard. Give them a bed free of that family for a few seasons, following the rotation guide on this site.