The USDA Zone info is a great tool for gardeners to help us determine your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

In Ontario you can determine when it's possible to plant cosmos by referring to the USDA zone info.

Planting Calendar for Cosmos

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

Since cosmos are barely cold tolerant you can plant them a bit earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant cosmos 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 cosmos and expect a good harvest is probably September. Any later than that and your cosmos may not have a chance to fully mature. Starting your cosmos indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

On average the last frost is on January 31 in Ontario. It might get as low as 30°F during the coldest months of winter.

Remember that the actual date of last frost is just an average because it is based on the USDA zone info for Ontario and it changes from year to year. Since half of the time in Ontario it frosts late in the year after January 31 be ready to cover your cosmos in the event of a surprise late frost.

USDA Zone Info for Ontario

Here is the info for USDA Zone 10a.

Average Date of Last Frost (spring)	January 31
Average Date of First Frost (fall)	December 15
Lowest Expected Low	30°F
Highest Expected Low	35°F

This means that on a really cold year, the coldest it will get is 30°F. On most years you should be prepared to experience lows near 35°F.

Plants to Grow in Ontario

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