When to plant in Thornhill, ON
Planting dates worked out from Thornhill's own frost records, not a generic zone chart.
Safe to plant out
May 18
1 year in 10 has a later frost
Average last frost
May 5
about a 50% chance of a later one
Average first fall frost
Oct 13
1 year in 10 by Oct 3
Frost-free days
160
median, 1991–2020
Station used: Toronto North York · 5.2 km away · station 187 m, town 175 m. How we match towns to stations
This season
Plan your garden.
Planting dates for common crops
| Crop | Start indoors | Plant out or sow | Harvest from |
|---|---|---|---|
| Tomato | Mar 23 – Apr 6 | May 18 – Jun 1 | Jul 12 |
| Sweet pepper | Mar 9 – Mar 23 | May 18 – Jun 1 | Jul 17 |
| Lettuce (leaf) | Mar 6 – Mar 13 | Apr 10 – Apr 24 | May 20 |
| Peas | — | Apr 10 – May 8 | Jun 4 |
| Bush beans | — | May 11 – Jun 1 | Jun 30 |
| Carrot | — | Apr 21 – Jun 2 | Jun 20 |
| Beet | — | Apr 21 – Jun 2 | Jun 10 |
| Potato | — | Apr 21 – May 12 | Jun 30 |
| Kale | Mar 6 – Mar 20 | Apr 17 – May 1 | May 30 |
| Broccoli | Feb 27 – Mar 13 | Apr 10 – May 1 | Jun 9 |
| Cucumber | Apr 20 – Apr 27 | May 18 – Jun 1 | Jul 7 |
| Summer squash and zucchini | Apr 20 – Apr 27 | May 18 – Jun 1 | Jul 2 |
| Winter squash | Apr 20 – Apr 27 | May 18 – Jun 1 | Aug 6 |
| Sweet corn | — | May 11 – Jun 1 | Jul 10 |
| Onion (from sets) | — | Apr 10 – May 1 | Jul 9 |
| Garlic | — | Sep 29 – Oct 27 (fall) | following summer |
| Spinach | — | Apr 10 – May 8 | May 18 |
| Basil | Apr 6 – Apr 20 | May 18 – Jun 1 | Jul 14 |
Thornhill's weather over time
How the growing season has shifted here, year by year, from the station's own records.
Each year's last spring frostLong-term trend
See the data as a table
| Year | Last spring frost |
|---|---|
| 1995 | Apr 30 |
| 1996 | May 13 |
| 1997 | May 18 |
| 1998 | Apr 28 |
| 1999 | Apr 25 |
| 2000 | May 3 |
| 2001 | Apr 29 |
| 2002 | May 22 |
| 2003 | May 4 |
| 2004 | May 4 |
| 2005 | May 13 |
| 2006 | May 7 |
| 2007 | May 13 |
| 2008 | May 1 |
| 2009 | May 18 |
| 2010 | May 11 |
| 2011 | Apr 22 |
| 2012 | Apr 30 |
| 2013 | Apr 26 |
| 2014 | Apr 24 |
| 2015 | May 23 |
| 2016 | Apr 28 |
| 2017 | Apr 23 |
| 2018 | Apr 29 |
| 2019 | Apr 29 |
| 2021 | May 8 |
| 2022 | Apr 29 |
| 2023 | May 18 |
| 2024 | Apr 26 |
| 2025 | Apr 17 |
| 2026 | May 12 |
Each year's frost-free daysLong-term trend
See the data as a table
| Year | Frost-free days |
|---|---|
| 1995 | 169 |
| 1996 | 143 |
| 1997 | 136 |
| 1998 | 184 |
| 1999 | 164 |
| 2000 | 148 |
| 2001 | 161 |
| 2002 | 144 |
| 2003 | 151 |
| 2004 | 153 |
| 2005 | 159 |
| 2006 | 158 |
| 2007 | 168 |
| 2008 | 158 |
| 2009 | 146 |
| 2010 | 154 |
| 2011 | 183 |
| 2012 | 160 |
| 2013 | 185 |
| 2014 | 169 |
| 2015 | 146 |
| 2016 | 164 |
| 2017 | 176 |
| 2018 | 167 |
| 2019 | 166 |
| 2021 | 178 |
| 2022 | 156 |
| 2023 | 157 |
| 2024 | 173 |
| 2025 | 191 |
Each year's average temperature, April to SeptemberLong-term trend
See the data as a table
| Year | Growing-season temperature |
|---|---|
| 1995 | 15.9 °C |
| 1996 | 15.5 °C |
| 1997 | 15.1 °C |
| 1998 | 17.7 °C |
| 1999 | 17.4 °C |
| 2000 | 15.6 °C |
| 2001 | 16.8 °C |
| 2002 | 16.9 °C |
| 2003 | 15.9 °C |
| 2004 | 15.8 °C |
| 2005 | 17.5 °C |
| 2006 | 16.9 °C |
| 2007 | 16.9 °C |
| 2008 | 16.4 °C |
| 2009 | 15.7 °C |
| 2010 | 17.8 °C |
| 2011 | 17.2 °C |
| 2012 | 17.6 °C |
| 2013 | 16.5 °C |
| 2014 | 16.2 °C |
| 2015 | 17.2 °C |
| 2016 | 17.6 °C |
| 2017 | 16.7 °C |
| 2018 | 17.5 °C |
| 2019 | 16.4 °C |
| 2021 | 17.5 °C |
| 2022 | 17.4 °C |
| 2023 | 16.7 °C |
| 2024 | 18.1 °C |
| 2025 | 17.8 °C |
What this means for you: Since 1995, Thornhill's last spring frost has come about 2 days earlier per decade, on average. The frost-free season has grown by about 6 days per decade. Year-to-year swings are large, so keep using the safe date rather than the trend.
Source: daily records from Toronto North York (NOAA GHCN-Daily, from Environment and Climate Change Canada). Years with too many missing days are left out.