One of the best tools that you have as gardeners to help us estimate your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

You should be able to figure out when you can plant primroses by looking at the USDA zone info for Ontario.

Planting Calendar for Primroses

Frost tolerance for primroses:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Since primroses are very cold tolerant you can plant them a lot earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant primroses in Ontario is February. However, you really should wait until March if you don't want to take any chances.

The last month that you can plant primroses and expect a good harvest is probably September. Any later than that and your primroses may not have a chance to really do well. You can get started a little bit earlier by starting your primroses indoors.

Last Frost Date

In Ontario the average date of last frost happens on April 15. It might get as low as -15°F during the coldest months of winter.

Since the USDA zone info for Ontario may not be accurate from year to year the actual date of last frost changes from year to year. Half of the time in Ontario you get surprised by a frost after April 15 so be sure to be ready to protect your primroses in the event of a late frost.

USDA Zone Info for Ontario

Here is the info for USDA Zone 5b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-15°F
Highest Expected Low	-10°F

This means that on a really cold year, the coldest it will get is -15°F. On most years you should be prepared to experience lows near -10°F.

Plants to Grow in Ontario

You may be interested in your other planting guides for Ontario.