Before planting it is a good idea to find your USDA Zone info to determine your garden schedule. 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 estimate when it's a good idea to plant dahlias by reviewing the USDA zone info for Ontario.

Planting Calendar for Dahlias

Frost tolerance for dahlias:	Not tolerant of frost.
When to plant:	After the last frost has passed.

Dahlias do not do well in cold weather which tells us that it's important to wait until it warms up after the last frost has passed before you can plant them.

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

The last month that you can plant dahlias and expect a good harvest is probably August. If you wait any later than that and your dahlias may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your dahlias indoors.

Last Frost Date

On average the last frost is on April 15 in Ontario. It might get as low as -15°F during the coldest months of winter.

Since the USDA zone info for Ontario is just an average the actual date of last frost changes from year to year. Half of the time in Ontario last frost occurs after April 15 so be sure to be ready to protect your dahlias 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.