Editorial Standards & Data Sources
Every frost date, planting window, and growing recommendation on GrowersGuide.ca is built on a stated source, a defined method, and a documented review schedule. This page explains exactly how the site is researched, written, and kept current.
Where our data comes from
- Frost dates & growing-season length — Environment and Climate Change Canada (ECCC) climate normals, currently the 1991–2020 dataset. Where a city's official weather station sits outside the urban core, we note it on the page.
- Hardiness zones — Natural Resources Canada's Canadian Plant Hardiness Zone Map (most recent revision).
- Crop maturity days and indoor-start windows — established horticultural references (provincial agricultural extension publications, Vesey's / William Dam / OSC seed catalogue specifications) cross-checked against ECCC frost dates for the relevant zone.
- Pest and disease information — provincial agriculture ministry pest factsheets (OMAFRA for Ontario, BC Ministry of Agriculture, Alberta Agriculture and Forestry) and university extension publications.
- Pet-safety information for houseplants — the ASPCA Toxic and Non-Toxic Plant List.
How dates are derived
"Last frost" on this site is the 50th-percentile historical average last spring frost from the city's ECCC station — meaning roughly half of years see the last frost earlier and half later. Where suburbs or neighbourhoods differ materially from the central station (Toronto waterfront vs. Brampton, Vancouver vs. Fraser Valley), we publish the variation alongside the headline figure.
Indoor seed-start dates count backwards from a city's last frost: 6–8 weeks for tomatoes, 8–10 weeks for peppers, 4–6 weeks for brassicas, and so on, using ranges established by horticultural references. Transplant and direct-sow dates apply the appropriate buffer past last frost (zero for hardy greens, one to two weeks for warm-season crops).
Frost dates and zones are averages, not forecasts. We say so on every page, and we recommend a one- to two-week buffer past the average for frost-sensitive crops.
Review & update schedule
- Year-in-title rollover — the time-sensitive page titles (frost dates, planting windows) are updated each January so they reflect the current year.
- Annual content review — planting calendars, crop maturity windows, and pest information are reviewed at least once per growing year against current ECCC and provincial agriculture publications.
- Hardiness zone updates — we adopt new Natural Resources Canada zone maps within one growing season of publication.
- Data-source upgrades — when ECCC publishes a new climate normal (currently 1991–2020; the next set is expected in the early 2030s), frost dates are recalculated and the page methodology block is updated.
Corrections policy
If a date, recommendation, or fact on the site is wrong, we want to fix it. Send the page URL and a short note explaining the issue through the feedback page. We aim to confirm receipt within seven days and to make verified corrections within two weeks of confirmation. Material corrections are reflected in the page's dateModified schema field and in the sitemap.
For frost-date or zone disputes specifically, we ask for the ECCC station identifier or the alternative source you're citing, so the change can be made against an authoritative reference rather than anecdote.
Conflict-of-interest & affiliate disclosure
Some product mentions on the site use affiliate links. These are disclosed individually on the pages where they appear and collectively on the affiliate disclosure page. Product recommendations are based on suitability for the Canadian climate and home-gardener use, not on commission rates — if a non-affiliate product is the better choice for a given page, we name it without a link.
Frost dates, planting calendars, and growing recommendations are never altered to favour an affiliate product.
AI tooling disclosure
Some pages on this site are drafted with the assistance of AI writing tools. Every page so produced is reviewed against the data sources listed above before publication and is subject to the same annual review and corrections policy. Frost dates, planting windows, and pest information are taken from the cited primary sources — not invented by an AI tool.
Contact the editors
Corrections, source disputes, and editorial questions: feedback page.
More on who we are and how the site is run: About GrowersGuide.ca.