In Alberta, turnips go in from mid-May onward. A second sowing in summer works if the roots have time to finish before fall frost. Both dates hang on two Calgary averages: May 21 for the last spring frost and September 16 for the first fall frost. Neither is a safe date. Each is the midpoint of a spread, and that changes how you use them.
The short answer for Alberta
Start sowing turnips around May 21, the mean last spring frost at the Calgary International station, and keep going until you run out of days before September 16, the mean first fall frost. Those are Environment and Climate Change Canada figures from the 1981-2010 normals. They are averages, not guarantees: in one year out of two, the last spring frost falls later than May 21.
The fall date works the same way. Frost arrives before September 16 in about half of years and after it in the other half. The gap between the two means is roughly 118 days, a frost-free stretch of about four months in an average year, with plenty of room on either side in a bad one.
Turnips are forgiving about that uncertainty. They tolerate a light frost better than beans or squash, so you do not have to wait for the May 21 midpoint to pass. Once the bed is workable and the soil is no longer a cold, soggy clump, a first sowing is reasonable. Treat May 21 as the point after which the odds of a hard spring frost get much lower, not as a green light.
For a fall crop, count backward. Take the days to maturity printed on your seed packet, add a couple of weeks of cushion, and subtract from September 16. The result is your last sowing date. A quick turnip leaves a lot of room. A slow rutabaga leaves very little, which is why rutabaga belongs in the ground at the start of the window, not the end. Variety choices are covered in The Best Turnips and Rutabaga for Alberta, and the broader crop picture is in Growing Turnips and Rutabaga in Alberta.
One caveat on the numbers. They come from a single airport station, and a province is not one climate. This page also has no rainfall or summer heat data for Alberta, so the calendar here rests on frost dates alone.
What will not work here
Treating May 21 as a finish line for frost fails. Since half of years see a later frost, a gardener who waits for “safe” weather sows into a calendar that may never offer it. A gardener who sows a hardy crop like turnips early and reseeds gaps loses a little seed, not a season.
Late-sown rutabaga also fails. It is the long-season member of the family and wants most of the summer. With only about 118 days between the mean frosts, a rutabaga sown after the start of summer is gambling that fall comes late. In the half of years when frost arrives before September 16, you get leaves and a thin root. If you want rutabaga, plan around the early part of the window.
Another trap is borrowing a calendar from a US source. American frost dates on this site use the 1991-2020 normals, while the Canadian figures here cover 1981-2010. The periods differ, the stations differ, and a Montana or Idaho sowing schedule says nothing reliable about Calgary or Edmonton. Copying one is a good way to be off by weeks.
Leaving roots in the ground to overwinter is not a plan either. The mean daily minimum of the coldest month is -13.2 °C (8.2 °F), and that is an average of the lows, not the record. Cold snaps run well below it. Turnips and rutabaga are harvested and stored, not left in the bed for spring. Lift them after the first hard frosts and move them to a cold, humid spot.
The last failure is data you cannot see. This page does not have Alberta rainfall or summer temperature figures, so it cannot tell you whether to water weekly or whether a July sowing will bolt in your yard. A heat wave in the weeks after a midsummer sowing can leave roots woody or sends plants to seed, and a dry spell can stall germination. Those are local risks to check with your own county, which is where the later sections point you.
What changes across Alberta
The reference figure here is Canadian hardiness zone 4a, from Natural Resources Canada, for the reference city of Calgary and based on 1991-2020 normals. It is not a USDA zone and does not convert to one. Natural Resources Canada says there are no simple conversions: its zone 4a overlaps nine USDA zones, from 3a to 7a, because the Canadian system uses seven climate variables and the USDA system uses one.
It is also not the zone of the whole province. Alberta runs from the southern prairies and foothills to the boreal north, and this page does not have a full spread of zones to quote. There is no single answer for the province. What the data does show is that northern and upland districts run weeks behind Calgary, so the frost dates above shift later in spring and earlier in fall wherever you are north or higher up.
If you garden in the north or at altitude, move your whole calendar in the direction that shortens the season. Start later in spring, since cold soil delays germination more than a calendar date helps. Pull the last-sowing date for fall crops earlier by a week or more, and favor the faster turnips over rutabaga. A foothills garden with a cold-air pocket can behave like one hundreds of kilometers north.
To find where you stand, use the Canada’s Plant Hardiness Site map from Natural Resources Canada and look up your own municipality. Do not assume your zone from this page, and do not assume it matches a neighbor’s, because the map is built to show differences across short distances.
Where to check this for your own county
The state-level answer here is a starting point. For the version that fits your county, go to Alberta Agriculture and Irrigation, the provincial agriculture department that covers what extension services do in US states. Look for two things there: a local planting calendar for your area, and any vegetable varieties that have been trialled in your county or a similar one.
A trial result carries more weight than a general recommendation. If a variety of turnip or rutabaga has been grown in plots near you and finished before frost, that outranks anything this page can say from one airport’s averages. The same goes for a local calendar that has been built from observations in your own climate.
A county recommendation beats a provincial one, and this page is the provincial one. It works from a single reference station and a single zone figure, and Alberta is large enough that those numbers will be wrong for many readers. When the county source and this page disagree, trust the county.
If you cannot find a county-level calendar, ask at a local garden club or an agricultural office. People who have grown root crops in your soil for years often know the real last-sowing date better than any published normal.
Checking this against your own garden
Your garden outranks every date on this page. Three observations cost nothing and tell you more than a calendar can.
- Soil warmth by feel. Dig a handful from the bed in spring. If it crumbles and does not feel icy, it is ready. If it clumps and stays cold, wait. A slope facing south warms sooner than a low corner, and the difference can be days.
- First true leaves. Sow a few turnip seeds early and watch for the first true leaves, the ones that come after the rounded seed leaves. If they appear quickly, your bed warms fast. If they lag, plan later sowings and a shorter fall window.
- Your own first fall frost. Note the date frost first blackens tender plants such as squash or basil. Compare it with September 16, and you learn whether your yard runs earlier or later than Calgary.
Write the dates down for a couple of seasons. A garden notebook beats a published normal because it records your own microclimate: the wind, the shade, the hollow where cold air settles.
The Moon calendar is a separate, older custom: see when to plant turnips by the moon, written as tradition rather than fact.
Common questions
Can I sow turnips before May 21 in Alberta?
Yes, once the soil is workable. Turnips tolerate light frost better than many vegetables. May 21 is the average last frost, so in half of years frost comes later, and a hard freeze can still catch seedlings.
Is May 21 a safe planting date?
No. It is a mean date from the Calgary International station for 1981-2010, not a probability of safety. In one year out of two, the last spring frost falls later.
Can I sow turnips again in summer for a fall harvest?
Yes, if the roots can finish before the first fall frost. Count backward from September 16 using the days to maturity on the packet, plus a cushion. Half of years bring frost earlier than that date.
Do these dates apply to Edmonton or northern Alberta?
Not exactly. The figures come from Calgary, and northern and upland districts run weeks behind it. Check your own municipality on the Natural Resources Canada hardiness map and with your local agricultural office.
One last nuance: the frost dates here use 1981-2010 normals, while the hardiness zone uses 1991-2020. The two are not from the same period, so a warmer recent decade could mean your real window sits a little wider than the one printed here.