Most unusual root crops in New Brunswick are planted around one date: May 23, the average last spring frost at Moncton. Hardy roots such as parsnip and salsify go in before it. Tender, long-season ones such as oca and yacon wait until after it. That date is a midpoint, not a promise, and the gap between it and the fall average is shorter than many seed packets assume.
The short answer for New Brunswick
Sow hardy roots as soon as the soil can be worked in spring, which is normally before May 23. Set frost-tender ones out only after that date, and a week or two later is safer. The numbers come from Environment and Climate Change Canada’s Canadian Climate Normals (1981-2010) for the Moncton station: last spring frost on average May 23, first fall frost on average October 2.
Both are mean dates, not safe dates. In one year out of two the last spring frost falls later than May 23, and in one year out of two the first fall frost arrives before October 2. Each date marks the middle of a window of risk, not the edge of one.
Count the days between the two averages and you get 132. A crop that needs 120 days from sowing to harvest, measured back from October 2, has to be in the ground by about June 4. That works only in an average year, and half of all years are worse than average.
| Type | Examples | When to plant |
|---|---|---|
| Hardy taproots | Parsnip, salsify, scorzonera, Hamburg parsley | Direct sow as soon as the soil is workable, ahead of May 23 |
| Hardy perennial roots | Jerusalem artichoke, horseradish | Plant tubers or crowns in early spring |
| Root celery | Celeriac | Start indoors, transplant after May 23 |
| Tender long-season tubers | Oca, yacon, mashua | After May 23 with a margin, expecting a modest crop |
One caution on the source: the figures come from a single station, Moncton, and a province is not one climate. They also cover 1981-2010, an older period than the 1991-2020 normals used for US pages on this site. The wider picture is in Growing Unusual Root Crops in New Brunswick, and The Best Unusual Roots to Grow in New Brunswick covers which ones deserve bed space.
What will not work here
Yacon is the clearest casualty. It is usually grown over a very long frost-free season, and New Brunswick offers 132 days between the average frosts. Even in a good year the plant is barely established when the cold arrives. Oca fails differently. It starts forming tubers late, as days shorten, and frost on October 2 (or earlier, in half of years) kills the foliage just as the tubers begin to swell. Without a tunnel or greenhouse, expect a handful of marble-sized tubers.
Treating May 23 as the all-clear is the second mistake. Plant celeriac or oca on that date and you are betting on a coin flip, because frost comes later than the average in one year out of two. A cheap row cover or a few upturned buckets turns that gamble into a nuisance.
Waiting for the “safe” date with hardy roots wastes their best weeks. Parsnip seed is slow to germinate in cold soil, and a sowing made in mid-June has little time to size up. Roots that shrug off a light frost should go in early, not follow the tomatoes.
Winter ends other plans. The mean daily minimum of the coldest month at Moncton is -13.9 °C (6.9 °F), and that is an average night, not the record low. Real cold snaps run well below it. Oca, yacon and mashua tubers will not survive in an unprotected bed, so they have to be lifted and stored indoors. Jerusalem artichoke and horseradish take the cold in stride. Parsnips can stay in the ground too, but only under a thick mulch laid before the soil freezes hard. Once it is frozen solid, you cannot dig them until it thaws.
Rainfall and humidity are not among the verified figures for this page, so it does not judge how tight your spacing can be. Give every root a bit more room than the packet minimum if your summers run damp.
What changes across New Brunswick
The reference city for this page falls in zone 5a of Canada’s plant hardiness system, based on 1991-2020 normals from Natural Resources Canada. That is not a USDA zone and does not convert to one. NRCan says there are no simple conversions between the two systems, and its own example is that Canadian zone 4a overlaps nine USDA zones, from 3a to 7a. The Canadian system uses seven climate variables, the USDA system one.
So there is no single answer for the province. The 5a figure describes one reference city, and this page holds no other values to build a spread from. Plant hardiness zones are one thing, frost dates another, and the two come from different periods (1991-2020 for the zone, 1981-2010 for the frosts), so treat them as rough guides, not as a matched pair.
Northern and upland districts run weeks behind Moncton. A gardener there should push every date later in spring and pull the fall deadline earlier. Leaning on hardy taproots, Jerusalem artichoke and horseradish makes sense, and tender tubers should be reserved for a protected spot. A sheltered south-facing bed, a low pocket where cold air settles, and a hilltop can behave like three different districts inside a single yard.
To see where your own municipality sits, use Canada’s Plant Hardiness Site and look up your town. Do not infer it from the reference city on this page.
Where to check this for your own county
This page gives the provincial picture, built from one weather station. A county recommendation beats it, and a recommendation from your own district beats the county’s. Start with Agriculture and Agri-Food Canada. The provincial department’s own site refuses automated checks, so the federal department is linked here because it can be confirmed to load. From there, follow the links to provincial agriculture services.
Once you reach a regional or provincial source, look for two things:
- A local planting calendar with frost dates from the weather station closest to you, not the Moncton figures used here.
- Lists of varieties trialled in your county, especially any that include parsnip, celeriac, salsify or other root crops.
Planting calendars are often published one crop at a time, not one per province, so look for the calendar of the crop you actually grow. Trial results matter even more than dates. A variety that finished well in your county’s soil and season beats one that merely looks right on paper.
Checking this against your own garden
Every date on this page loses to what your own bed is doing. Three signs are worth watching, and none needs equipment.
Soil warmth, by feel. Push your bare hand a few inches into the bed in the morning. If it feels cold and clammy, hold off on tender transplants and seeds that sulk in the cold. A south-facing slope that warms days before a shaded corner has shown you your own early zone.
The first male flowers. Squash and zucchini plants send up male flowers a little before the female ones. If you grow them, the date they appear tells you how fast your garden is warming compared with last year, or with a neighbor’s. A late flush means a slow, cool season, which is a good reason to skip long-season roots.
The first true leaves. The two seed leaves that emerge first do not count. The first set of true leaves means the seedling has taken hold. If your parsnips reach that stage in two or three weeks, your bed is warming at a normal pace. If they take far longer, the bed is cold or shaded, and you should favor faster crops.
Common questions
Can I plant tender roots on May 23 in New Brunswick?
You can, but the odds are even. May 23 is the average last spring frost at Moncton, so in one year out of two the frost falls later. Wait a week or two, or keep a row cover ready.
Which unusual roots can stay in the ground over winter?
Jerusalem artichoke and horseradish are hardy perennials, and parsnips will overwinter under a thick mulch. The mean daily minimum of the coldest month is -13.9 °C at Moncton, which kills oca, yacon and mashua tubers left outside.
Must I harvest everything by October 2?
No. October 2 is the average first fall frost, and frost arrives earlier in half of years. Hardy taproots tolerate it, and many gardeners leave them in for later digging. Tender tubers should be lifted before frost, so watch the forecast.
Do the Moncton dates apply to my town?
Not necessarily. They come from one station, and northern and upland districts run weeks behind it. Check your regional frost dates before sowing. If you compare with US neighbors, remember that Canadian normals here cover 1981-2010, while US figures on this site cover 1991-2020.