Écodici

Free tool · Agriculture and Agri-Food Canada data

When to sow in my town?

Enter your town: you get your frost dates, how warm your season is and, for 31 vegetables and herbs, when to start seeds indoors, sow in the garden and plant out.

1,145 Quebec towns and districts. If you use your location, it stays in your browser.

How your dates are calculated

Frost dates and degree-days come from Agriculture and Agri-Food Canada’s 1991-2020 climate normals, calculated on a 10 km grid. The average last frost is the average date of the last night at or below 0 °C before July 1.

At that average date, there is still about one chance in two of frost. In the 88 Quebec weather stations with enough data (Environment Canada 1981-2010 normals), the risk drops to about one chance in ten 16 days later, at the median. We call that day the “safer date”, and it anchors the planting dates. In the fall, the risk of a first frost reaches about one chance in ten roughly 15 days before the average first frost.

The sowing windows are based on the vegetable sowing calendar of the Montréal Botanical Garden (Espace pour la vie) and on extension guides from the universities of Maine and North Dakota, regions with a climate like ours, brought back to your safer date. Warm-season vegetables need soil of at least 10 to 16 °C, according to University of Minnesota Extension; peas, spinach, lettuce and radishes can be sown once the soil reaches 4 to 10 °C.

Your yard has its own climate

A value for a 10 km square doesn’t tell the whole story. In a hollow, near a cold lake or at higher elevation, frost often comes later in spring and earlier in fall: some weather stations record their last frost two to three weeks after the grid average for their area. Near a south-facing brick wall, in town or near the river, it’s often a little earlier. And every spring is different: always check the forecast before putting your seedlings out. Microclimates: why your yard can gain half a zone

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Frequently asked questions

Where do the frost dates come from?

From the derived normal climate data of Agriculture and Agri-Food Canada for 1991 to 2020, calculated on a 10 km grid across Canada. The last spring frost is the average date of the last night at or below 0 °C before July 1.

What is the “safer date”?

At the average date of the last frost, there is still about one chance in two of another frost. In the 88 Quebec weather stations with enough data (Environment Canada normals, 1981 to 2010), the remaining risk drops to about one chance in ten, at the median, 16 days after the average date. That is the date the calculator uses to place your plantings.

What are degree-days?

Each day from April to October, we add up the degrees by which the average temperature exceeds 5 °C. The total measures the heat available to grow and ripen your vegetables: the more there are, the easier it is for tomatoes, peppers and melons to ripen.

My yard is colder than my town. What should I do?

The values are averages for a 10 km square. In a hollow, near a cold lake or at higher elevation, frost often comes later in spring and earlier in fall. The gap can be large: some weather stations record their last frost two to three weeks after the grid average for their area. Add a week or two of caution if your yard is in a frost pocket.

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