Indiana gives unusual root crops a long, forgiving window, but the date to watch is the soil’s, not the calendar’s. Hardy roots like kohlrabi, turnips and horseradish go in first, celeriac follows as warmed-up transplants, and Jerusalem artichokes need a site chosen before any tuber is bought. Winter cold, not summer heat, decides what can stay in the ground.
When the soil is warm enough in Indiana
For Indianapolis, the last spring freeze at 32°F lands between April 9 and April 21, according to the NOAA NCEI 1991-2020 Climate Normals (30-70% probability band, station USW00093819). That is a probability, not a promise. Purdue puts the chance of a 32°F night after the published spring date at roughly 10%, so anything tender set out on the early edge of that range needs a cover within reach.
Why frost is only a stand-in
Frost dates are a proxy. Roots don’t care when the last freeze happened; they care how warm the soil is around them, and soil lags the air. A bed can be frost-free for two weeks and still be cold and soggy at trowel depth. The soil warms after the frost risk ends, not with it. Squeeze a handful from the planting depth: if it clumps into a wet ball, wait. If it crumbles, you are close.
Different types wait for different things. Turnips, rutabagas and kohlrabi germinate in cool ground and can go in as soon as the bed is workable, even a bit before the frost band closes. Horseradish crowns and root cuttings also go in early. Celeriac is the fussy one. It starts indoors, and a cold snap after transplanting can push it toward bolting instead of fattening a root, so it waits until the frost risk has truly passed.
Location shifts everything. Indianapolis is the reference point here, and southern Indiana runs earlier in spring (and later in autumn) than the north by a fortnight or more. A gardener near the Ohio River and one near Lake Michigan should not plant on the same Saturday.
Jerusalem artichokes: choose the site first
Before any technique, a warning. Jerusalem artichoke is effectively permanent once planted. Every fragment of tuber left behind regrows, and digging a patch out leaves plenty of fragments. It is the single most regretted planting in a vegetable garden. Put it where a permanent stand is the goal: a back corner, a strip along a fence, a bed bounded by pavement or a mown edge. Keep it away from beds you plan to rotate.
Once the site is settled, growing it is easy. Tubers go in as the soil becomes workable in spring, and the tall stems die back in autumn. Harvest only what you will use, and expect it to return.
One plain fact of the vegetable: Jerusalem artichokes store inulin instead of starch, and in many people that causes digestive discomfort. A small first portion is the sensible way to find out how you react.
How long the season lasts here
Count the days between the two frost bands. Take the later spring date (April 21) and the earlier fall date (October 21) and you get 183 days. Take the earlier spring date (April 9) and the later fall date (October 30) and you get 204. The fall dates come from the same NOAA NCEI 1991-2020 normals for Indianapolis. So the frost-free stretch runs from about six months to a little under seven, depending on how the year behaves.
What does that length allow? A second sowing, for one thing. In a short-season state the first sowing is the only sowing, and every decision rides on it. Here, turnips, rutabagas and kohlrabi can be sown in spring, then again in late summer for a fall crop that ripens in cooling weather. Many gardeners find the fall planting the better one, since roots that size up in cool autumn weather tend to be sweeter and less woody than those that matured through July. The site’s succession sowing guide lays out how to stagger the dates.
The length also changes the transplanting question. Celeriac is the long-season member of this group, and 183 to 204 days makes it a realistic crop here, not a gamble, provided it starts indoors and goes out as sturdy transplants. Before planting, check the root ball: pale, white roots filling the cell are what you want, while circled or damaged roots are a poor start for a crop that is, after all, a swollen root. Kohlrabi, turnips and rutabagas dislike root disturbance and do better sown where they will grow.
Neighboring states have their own windows, and the comparison is useful if you garden near a border. See Growing Unusual Root Crops in Delaware and Growing Unusual Root Crops in Pennsylvania for how the same crops fare there.
Heat and water in Indiana
The verified figures for this page do not include a count of days above 90°F or a summer rainfall total for Indiana, so none are quoted here. Estimating them would be worse than leaving them out. What can be said is general: Indiana summers are warm and humid, and that combination shapes root crops in two ways. Heat stress pushes cool-season roots such as turnips and kohlrabi toward woodiness, bitterness and bolting, and humidity favors foliar disease and rot at the crown.
Water matters as much as heat. Celeriac wants steady moisture from transplanting to harvest, and a pattern of drought followed by downpour tends to produce cracked or hollow roots. A thick layer of straw or shredded leaves keeps the soil cooler and evens out the swings. Overhead watering late in the day leaves foliage wet through the night, which is exactly what leaf diseases want, so water at the base, in the morning.
Winter is where Indiana’s numbers are firmer. The mean daily minimum of the coldest month at Indianapolis is 20.9°F (NOAA NCEI Climate Normals 1991-2020). That is an average of nightly lows, not a record, so individual nights go lower. The USDA Plant Hardiness Zone Map 2023 places Indiana in zones 5b to 7a, a territory-wide range that runs colder in the north and milder in the south. Treat Indianapolis as the reference and expect your own place to differ.
That winter low sorts the crops. Horseradish and Jerusalem artichokes are perennials that handle these winters in the ground, with or without mulch. Rutabagas tolerate light frost and can stay under a heavy mulch for a while. Celeriac, kohlrabi and turnips are better lifted before the soil freezes hard. Whatever comes out gets inspected: a soft patch, a weeping spot or a moldy crown ends the question, and a root that merely looks sound is not thereby safe to store or eat. Trim the sound ones, store them cool and damp, and check them often.
Which these root crops suit Indiana
Indiana’s facts point to a few criteria. The long window means the earliest-maturing types are not a necessity, though they make a second sowing easier. Warm, humid summers make disease resistance the first thing to look for on a seed packet. Heat favors types given airflow and shade at the root, which in practice means mulch, spacing, and a bed that is not walled in by taller plants.
| Type | What Indiana asks of it | Practical move |
|---|---|---|
| Celeriac | Needs the full season; dislikes uneven water and late cold | Start indoors, transplant after frost risk, mulch and water steadily |
| Kohlrabi | Turns woody in summer heat | Sow in spring and again late summer |
| Turnip and rutabaga | Cool-season; humidity brings disease | Prefer disease-resistant types, space for airflow |
| Horseradish | Hardy through winter here | Leave in place, dig as needed |
| Jerusalem artichoke | Hardy and aggressive | Plant only in a permanent, contained site |
One family point matters for rotation. Turnip and rutabaga are brassicas, and so are kohlrabi and horseradish. They share their troubles with cabbage, kale and mustard, so a gardener who rotates them into a cabbage bed has rotated nothing. The site’s rotation guide covers the sequence.
Horseradish carries a preparation warning. Grating a fresh root releases compounds that burn the eyes and airways, and this is not a joke. Work with good ventilation, keep your face away from the bowl, and open a window or grate outdoors.
This page names no varieties, and that is deliberate. The only recommendation that means anything is one trialled where you garden, and Indiana spans USDA zones 5b to 7a, so a type that thrives near Evansville may sulk near South Bend. Purdue Extension and your county office can tell you which varieties have been tested locally. For a wider view of the crops themselves, see Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes.
Common questions
When can celeriac go outside in Indiana?
After the frost risk has passed. At Indianapolis that band runs April 9 to April 21, and a small chance of a later freeze remains, so keep covers handy. Wait too for soil that has warmed, since cold ground after transplanting can encourage bolting.
Can Jerusalem artichokes stay in the ground over winter?
Yes. They are hardy through Indiana winters, and the tubers store well in the soil, but that is also why leftovers regrow. Inspect anything you dig and discard soft, weeping or moldy tubers.
Is northern Indiana different from Indianapolis?
Yes. Spring arrives earlier in the south and autumn later, by a fortnight or more compared with the north. Shift your dates accordingly and use your local frost record when you have one.
Which varieties should I buy?
Ask Purdue Extension for varieties trialled in Indiana. Choose by type first: disease resistance for turnips and rutabagas, and a long-season, steadily watered start for celeriac.