Yes, and the calendar is generous. At the Newark reference station, the last spring freeze falls between March 29 and April 6 and the first fall freeze between November 4 and November 16. That leaves room for celeriac, kohlrabi, horseradish, Jerusalem artichokes, turnips and rutabagas. The catch is that these crops follow soil, not dates, and most New Jersey yards run a week or two behind Newark.
When the soil is warm enough in New Jersey
Start with the date everyone wants. NOAA’s 1991-2020 U.S. Climate Normals put the last spring 32°F freeze at Newark between March 29 and April 6 (that is the 30-70% probability band, from the NOAA NCEI normals file for the airport station). A frost date is a probability, not a promise, so a late cold snap in any given year is part of the deal.
Those dates also describe an airport surrounded by pavement, which holds heat. Suburban and rural gardens usually see the last spring frost later, often by one to two weeks, and more at elevation. Check your own county before you pencil anything in.
The bigger point is that frost is only a proxy. Root crops wait for warm soil, and soil warms after the frost risk ends, not with it. Air can climb into the 60s while the top few inches of a bed are still cold and wet, and that is where seeds sulk and transplants stall. A soil thermometer pushed in at planting depth, read in the morning, tells you more than any chart.
Site the Jerusalem artichoke before anything else
Jerusalem artichoke is effectively permanent once planted. Every fragment of tuber left in the ground regrows, and digging the bed over tends to scatter more pieces. It is the most regretted planting in a vegetable garden, so choose the spot first: a bed you can give up for good, with a hard edge such as a lawn border, a fence line or a container sunk to the rim. Never put it in the middle of a rotation.
Plant it in spring once the ground is workable. Eat a small first portion. Jerusalem artichokes store inulin rather than starch, and many people get digestive discomfort from it. A small serving is the sensible way to find out which group you are in.
The rest of the group
Kohlrabi, turnips and rutabagas tolerate cool soil and can go in as soon as the bed is workable. Horseradish roots can also go in early, since the plant is a hardy perennial. Celeriac is the fussy one. Its transplants dislike a cold start, and a chill early in life can push the plant toward bolting, so hold it until the soil has settled warm and the weather has stopped swinging.
Varieties are another matter. This page names none, because the ones trialled in New Jersey are the only ones worth recommending, and Rutgers Cooperative Extension is where those results live. The broader overview is in Celeriac, Kohlrabi, Horseradish and Jerusalem Artichokes.
How long the season lasts here
Count it out with the same Newark normals. From the earliest end of the spring band (March 29) to the earliest end of the fall band (November 4) is 220 days. From the later ends (April 6 to November 16) it is 224 days. Call it roughly 220 to 224 days between freezes at the reference station, about 31 weeks.
Subtract a week or two from each end for a typical suburban or rural garden, and the window is still long by northern standards. Gardeners in colder places work with a very different calendar. Growing Unusual Root Crops in Alberta shows how much that changes the plan, and Growing Unusual Root Crops in New York covers the neighbor to the north.
What does a window this long allow? Mainly, a second sowing. A quick crop such as kohlrabi or turnip can go in early, come out, and be followed by another sowing in late summer that matures in the cool of fall. Fall roots often eat better than spring ones, because cool nights slow growth and tend to give a milder, less woody result. The staggering of sowings is laid out in the succession sowing guide on this site.
The length also changes the transplanting question. A short season makes the first sowing the only one, and then every setback counts. Here, a root that gets disturbed or stunted can be replaced. Even so, turnips and rutabagas resent having their taproot handled and do best sown where they will stay, since a damaged root forks. Celeriac and kohlrabi are normally started in trays and moved, and with 220 days on the Newark calendar the long-season celeriac has room to finish, as long as it gets going on time.
Fall is the end that gets misjudged. The first-freeze band of November 4 to 16 belongs to the airport, and a rural garden may be hit earlier. Plan the last sowings to mature before your local first frost, not Newark’s.
Heat and water in New Jersey
This is where a regional page should lean on the count of days above 90°F and the summer rainfall. This page does not carry either figure for Newark, so it quotes neither. Guessing would be worse than leaving the gap. The nearest station’s NOAA normals, or Rutgers Cooperative Extension, will give you both.
Without those numbers, the garden itself is the better guide. Roots that get hot and dry, then a sudden soaking, split and turn woody. Even moisture, a layer of mulch over the root zone and a bit of afternoon shade on the hottest beds do more than any variety choice. If your summers instead run cool and damp, expect mildew, slow ripening and rot, and that calls for airflow and spacing.
Two facts that are in hand govern this group. The first is season length. With about 220 days between freezes at Newark, celeriac, the long one, can finish here, provided you start it on time and your own county does not lose too many weeks at either end.
The second is the winter low. The mean daily minimum of the coldest month at Newark is 25.5°F (NOAA NCEI Climate Normals 1991-2020). The USDA Plant Hardiness Zone Map 2023 puts the state across zones 6a to 7b, and that system rests on a single variable, the average annual extreme minimum temperature. Other parts of the state differ from Newark, and the colder inland and higher areas sit toward the lower end.
For the perennials, the answer is simple. Horseradish and Jerusalem artichokes are hardy across that range and can stay in the ground under mulch, so dig them when you need them. The hardy roots, turnips and rutabagas, can often be left in the ground under mulch too, but not past the point where the soil freezes hard, since they are harder to pull from frozen ground. Celeriac is less forgiving. Lift it before the soil freezes.
Lifted roots need inspection, not trust. Check each one before it goes into storage, and again while it is there. A soft patch, a weeping spot or a moldy crown ends the question for that root, and a firm, sound-looking exterior does not make it safe. This page gives no keeping times, because they depend entirely on the root, the conditions and the condition it went in.
Which these root crops suit New Jersey
Choose by type, reasoning from the facts above. A long season means you are not forced toward the very earliest, fastest types, though in a rural garden that loses a couple of weeks at each end, the earlier types for fall sowings are the safer pick. Where summers turn hot, favor crops that tolerate shade and airflow at the root, and mulch them. Where summers run humid, disease resistance becomes the first criterion on any seed packet.
| Crop | Fit with New Jersey’s facts | What to watch |
|---|---|---|
| Celeriac | The ~220-day Newark window lets it finish | Cold early on, then uneven water; lift before the soil freezes |
| Kohlrabi | Fits spring and a second, late-summer sowing | Heat stress in midsummer; it is a brassica |
| Turnip and rutabaga | Hardy, well suited to fall crops | Sow in place; both are brassicas |
| Horseradish | Hardy through zones 6a to 7b, can stay mulched | Spreads; irritant fumes when grated |
| Jerusalem artichoke | Hardy, thrives with the long window | Permanent once planted; site it first |
Turnip, rutabaga and kohlrabi are brassicas. They share their pests and diseases with cabbage, kale and mustard, so rotating one into a cabbage bed rotates nothing. The rotation page on this site explains how to space them out.
On horseradish, grating the fresh root releases compounds that burn the eyes and airways, and this is no exaggeration. Grate in a well-ventilated space, keep your face and eyes away from the bowl, and open the container slowly.
No cultivar is named here, and that is deliberate. This page cannot source a variety trialled in New Jersey, and a made-up name is the error a gardener spots at once. The trial results and recommended varieties for your area are at Rutgers Cooperative Extension, and a county office can speak to the conditions where you live.
Common questions
Can I plant these crops on the last frost date?
Not by the date alone. Hardy crops such as turnips and kohlrabi can go in earlier, but celeriac and the warm-season plantings should wait until the soil, not the air, has warmed. Newark’s March 29 to April 6 band is a reference, and your county may be later.
Can I leave Jerusalem artichokes in the ground all winter?
Yes, they are hardy across New Jersey’s zones, which run from 6a to 7b on the USDA 2023 map. Any tuber left behind will regrow, so plan for that.
Does celeriac have time to finish in New Jersey?
At Newark’s reference figures, about 220 days separate the freezes, which is generous for a long-season crop. A rural garden loses some of that, so start early and check your county’s dates.
Which varieties should I buy?
Ask Rutgers Cooperative Extension. Varieties trialled locally are the only recommendation that counts, and this page does not hold that list.