The Best Sweet Potatoes to Grow in Northwest Territories

Choose the fastest-maturing sweet potatoes you can find: early, orange-fleshed types and compact bush-style vines, grown from slips under plastic or in containers. Around Yellowknife the frost-free stretch is short, and the real limit is soil warmth, not summer air. A late, sprawling variety won’t finish. Below, the numbers behind that call, and where your own garden may differ.

The short answer for Northwest Territories

The best sweet potatoes for the Northwest Territories are the earliest-maturing types, set out as purchased slips in a warmed bed, a raised container or under plastic. Look for short-season, compact or semi-bush vines, and skip anything marketed as a long-season, heavy-yield variety.

Here is where that comes from. At the Yellowknife A station, Environment and Climate Change Canada’s 1981-2010 normals put the last spring frost on average on May 25 and the first fall frost on average on September 18. Those are mean dates, not safe dates. In roughly half of years the last frost lands after May 25, and in roughly half the first fall frost arrives before September 18. Treat each as the middle of a window.

The season math

Between those two mean dates sit about 116 days. Sweet potatoes can’t use all of them. Slips set out on May 25 would meet cold soil and a coin-flip chance of another frost. Transplant around June 10, purely as an illustration, and you’re left with about 100 days before the average first frost, less any margin you want for an early one. Typical seed-catalog maturity runs from roughly 90 days for the quickest types to 120 or more for the slowest, so only the fast end of that range fits comfortably. For the sowing and transplant timing in more detail, see When to Plant Sweet Potatoes in Northwest Territories.

Choose by type, not by name

Names change between suppliers and seasons, and this page has no territorial trial results to rank named varieties. Types are more reliable guides, and a seed or slip catalog will tell you which category a variety falls in.

Days to maturity in catalogs assume warm soil from day one. In a cold northern bed, add a week or two in your head.

What will not work here

Slow varieties fail first, and the arithmetic is unforgiving. A 120-day type transplanted on June 10 would need until early October to size up. The average first frost at Yellowknife A is September 18, and half of years it comes sooner. A single frost blackens the vines, and roots that haven’t sized up by then stay pencil-thin.

Slow varieties and late transplanting

Planting too early fails just as reliably. Setting slips into open ground in late May, on the strength of the May 25 mean, puts them in cold soil with roughly even odds of a frost still to come. Sweet potatoes sulk in cold soil, stalling for weeks, and those weeks are the ones you don’t have. Waiting for a longer harvest in the fall is also a bet against the odds, because the first-frost mean means about half of years end sooner than you’d like.

Don’t read the heat record as a verdict. Yellowknife A averages 0.03 days a year at or above 32 °C and 0.45 days a year at or above 30 °C. Those count extreme days, and they don’t measure the growing season, which depends on the frost-free period and the summer means. What the numbers do say is that no heat wave will rescue a cold bed. Warmth has to be built in, with black plastic, a raised bed, a container against a south-facing wall, or a low tunnel.

Watering on a fixed schedule

Summer rain at Yellowknife A (1981-2010 normals) totals about 109 mm (4.3 inches) across June, July and August, out of 290 mm (11.4 inches) for the year. June is the driest summer month at 29 mm (1.14 inches), then July at about 41 mm (1.61 inches) and August at about 39 mm (1.55 inches). June is exactly when slips are trying to root, so don’t count on rain to settle them in.

The figure never works alone. On sandy or gravelly soil, a light rain sinks out of reach within the day, so a bed there may want water every couple of days in June. On clay, the same rain lingers for a week and waterlogging becomes the risk, especially in a cool bed where roots rot rather than grow. A fixed weekly schedule fails both ways. These are station normals for one airport, not a forecast, and a straight-sided jar left in your own bed settles the question better than any table.

What changes across Northwest Territories

A territory this size is not one garden. The only hardiness figure this page has is for Yellowknife, the reference city: zone 1b in the Canadian system, from Natural Resources Canada’s 1991-2020 normals. That is not a USDA zone and doesn’t convert to one. The Canadian system folds in seven climate variables where the USDA system uses one, and NRCan notes that Canadian zone 4a alone overlaps nine USDA zones, from 3a to 7a. The page doesn’t have zone figures for other communities, so it can’t give you the spread inside the territory. There is no single answer for the whole NWT.

The geography is enough to know the spread is real. The territory runs from the south shore of Great Slave Lake to north of the Arctic Circle, and the frost dates quoted above come from one airport station. Northern or upland districts run weeks behind it, as the Canadian normals themselves caution. A reader well north of Yellowknife should shift everything later and tighter: later transplanting, more protection, a container that can move indoors on cold nights, and a harder look at whether a greenhouse is the realistic home for the crop.

Readers in the south of the territory may find more room, though the page has no station figure to put a number on it. Local differences matter too. A south-facing wall, a spot near a lake, a town’s built-up warmth and a low frost pocket can each move your season by days. For the full picture of the crop, see Growing Sweet Potatoes in Northwest Territories.

To find your own zone, don’t guess from a neighbor’s. Look up your community on Natural Resources Canada’s Plant Hardiness Site and read the Canadian zone it gives, remembering that it won’t map onto a USDA number.

Where to check this for your own county

The Northwest Territories has no counties, so the local equivalent is your community or region. The place to start is the territorial government’s agriculture services, run through Industry, Tourism and Investment. Look there for two things: a planting calendar that fits your area, and any varieties trialled in or near your community. A trial in a garden or greenhouse near you says more than any national catalog.

This page doesn’t know whether that office publishes sweet potato guidance, so ask directly. Good questions: which short-season varieties have been grown locally, whether slips are available from nearby suppliers or have to be shipped in (and when), and what the typical last and first frost dates are for your community rather than for Yellowknife’s airport.

A local recommendation beats a territorial one, and this page is the territorial one. It rests on a single reference station and on 1981-2010 Canadian normals, which cover a different period from the 1991-2020 US figures used elsewhere on this site, so the two sets aren’t directly comparable. Treat the dates here as a starting frame and let a community gardener, a local greenhouse grower or a government agricultural contact correct them.

Checking this against your own garden

Your own observations outrank every date on this page. Three are worth watching, and none needs equipment you don’t already own.

• Soil warmth by feel. Push your hand four inches into the bed in the morning. If it still feels cool and damp, the slips will stall. A bed that warms early tells you it has good sun and drainage, and a slow one tells you to add plastic, raise it or move it.
• New leaves after transplanting. Fresh leaf growth on the slips, usually within a week or two, means the roots have taken hold. If nothing moves for three weeks, your microclimate is cooler than the station normals suggest.
• Frost marks on tender plants. Note the last frost that blackens tender growth in spring and the first in fall. Over two or three seasons, those dates show where your spot sits against the May 25 and September 18 means.

Add a jar for rainfall if you like, but the three observations above do the real work. Keep notes: a short log of dates beats memory by the second year, and it makes the local recommendations from the agriculture office far easier to apply.

Common questions

Can sweet potatoes be grown in the Northwest Territories at all?

Yes, with short-season types and added warmth. The mean frost dates at Yellowknife A leave about 116 days between them, and with a transplant date in June you have roughly 100 days to work with. This page has no territorial trial results, so treat it as workable with protection, not guaranteed.

Should I buy slips or start my own?

Either works, but your timing has to match the season. Slips are usually grown over roughly six to eight weeks indoors, so starting your own means beginning in spring well ahead of transplant. Buying avoids that work but means arranging delivery to arrive when your bed is warm enough.

Does the 32 °C count mean it is too cold for them?

No. Yellowknife A averages 0.03 days a year at or above 32 °C and 0.45 days at or above 30 °C, which counts extreme days only. What decides success is the frost-free period and summer means, and that is why the advice here is about season length and soil warmth.

Do the dates apply to communities far from Yellowknife?

Not directly. The frost dates and the zone 1b rating (Canadian system) belong to Yellowknife, and districts to the north or at altitude run weeks behind. For anywhere else, check the plant hardiness map and the territorial agriculture office, and keep your own frost log, which in a few seasons will be more reliable than any normal.