Alberta · Growing Zone 5a
Gardeners in Lethbridge, AB can expect the average last spring frost around May 15, and the first fall frost around October 2, based on historical Environment Canada frost data for the area. That gives Lethbridge a frost-free growing season of roughly 140 days. Actual frost dates shift by a week or two year to year, so use this as a planning baseline rather than an exact guarantee, and always check your local forecast before moving tender plants outside.
You have your Lethbridge frost dates. Now put them to work: GrowBlock counts back your indoor seed-starting weeks, marks your safe planting day, warns you before a frost, and lays your whole season out on one timeline.
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Most warm-season crops (tomatoes, peppers, squash) need transplanting only after the last frost has passed, and are usually started indoors 6 to 8 weeks before that date. Cold-hardy crops (peas, lettuce, spinach) can often go in the ground a few weeks before the last frost. As Lethbridge's first fall frost approaches in October, it's time to plan the last harvests for anything frost-sensitive still in the ground.
Approximate dates for common crops in Lethbridge, worked out from the local last frost around May 15. Warm crops go out after frost, cold-hardy crops a few weeks before it, and anything with an indoor start is counted back from its sow date.
| Crop | Start indoors | Sow / transplant out | Approx. harvest |
|---|---|---|---|
| 🍅 Tomato | April 10 | May 29 | August 17 |
| 🌶️ Pepper | March 27 | May 29 | August 12 |
| 🥒 Cucumber | — | May 22 | July 19 |
| 🥬 Zucchini | — | May 22 | July 11 |
| 🥬 Lettuce | — | April 24 | June 8 |
| 🥬 Spinach | — | April 24 | June 11 |
| 🫛 Peas | — | April 24 | June 25 |
| 🥕 Carrots | — | April 24 | July 1 |
| 🫘 Bush beans | — | May 15 | July 4 |
| 🥬 Kale | March 27 | April 24 | June 18 |
Guideline dates from Lethbridge's average frost window, not a guarantee. GrowBlock tunes these to each variety you plant and adjusts as you build your beds.
This calendar is a starting point. In GrowBlock every date is tuned to the exact varieties you plant and updates as you lay out your beds, and you can share the plan with whoever you garden with, changes show up for both of you.
Build your Lethbridge garden planAround May 15 on average, though it can vary by a week or two either way depending on the year.
Lethbridge is in zone 5a, with a frost-free season of about 140 days.
Now that you have your dates, here is how to put them to work through the season:
More how-to on the GrowBlock gardening blog.
See frost dates for all Canadian cities covered by GrowBlock.