Canada's Plant Hardiness Site
Ontario
| 1961-1990 zone | 1991-2020 zone | 1961-1990 hardiness index | 1991-2020 hardiness index | |
|---|---|---|---|---|
| Oakville | 6b | 7a | 66 | 72 |
| Oakwood | 5a | 5b | 53 | 56 |
| Oba | 1b | 2b | 18 | 26 |
| Odessa | 5b | 6a | 59 | 62 |
| Oil Springs | 6b | 6b | 66 | 69 |
| Oliphant | 5b | 6a | 57 | 61 |
| Omemee | 5a | 5b | 53 | 56 |
| Ompah | 4b | 5a | 45 | 51 |
| Onaping Falls | 3b | 4a | 38 | 44 |
| Opasatika | 1b | 2a | 17 | 23 |
| Orangeville | 5a | 5b | 50 | 56 |
| Orillia | 5a | 5b | 54 | 58 |
| Orléans | 4b | 5a | 49 | 54 |
| Orono | 5b | 6a | 59 | 62 |
| Orrville | 4b | 5a | 45 | 50 |
| Osgoode | 5a | 5b | 52 | 57 |
| Oshawa | 6a | 6b | 61 | 65 |
| Osnaburgh House | 1b | 2b | 15 | 29 |
| Ottawa | 5a | 5a | 50 | 54 |
| Otterville | 6a | 6b | 63 | 66 |
| Owen Sound | 5b | 6a | 57 | 61 |