One of the first steps you take when you are estimating your gardening schedule is find your USDA Zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

By checking out the USDA zone info for Ontario you should be able to figure out when it's a good idea to plant petunias.

Planting Calendar for Petunias

Frost tolerance for petunias:	Tolerant of a very small amount of frost.
When to plant:	Up to 3 weeks before last frost.

Petunias are barely cold tolerant which tells us that you can start planting them slightly earlier than plants that are more sensitive to the cold.

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

The last month that you can plant petunias and expect a good harvest is probably August. Any later than that and your petunias may not have a chance to fully mature. You can get started a couple of weeks earlier by starting your petunias indoors.

Last Frost Date

On average the last frost has passed is on April 15 in Ontario. You can expect an average low temperature of -15°F in the coldest months of winter.

Since the USDA zone info for Ontario is just an average the actual date of last frost can change quite a bit from year to year. Since half of the time in Ontario it frosts late in the year after April 15 be ready to cover your petunias in the event of one of those late frosts.

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.