One of the first steps you take when you are figuring out 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.

In Phoenix you can determine when to plant cosmos by checking out 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.

Cosmos are barely cold tolerant which tells us that you can plant them slightly earlier than other frost tender plants.

The earliest that you can plant cosmos in Phoenix 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 grow to maturity. You can get started a couple of weeks earlier by starting your cosmos indoors.

Last Frost Date

The average date of last frost is February 15 in Phoenix. You should expect an average low temperature of 25°F in the coldest months of winter.

It's important to remember that USDA zone info for Phoenix is not always accurate and the actual date of last frost can change quite a bit from year to year. Half of the time in Phoenix you get surprised by a frost after February 15 so just be sure to be ready to cover your cosmos if you have one of those late frosts.

USDA Zone Info for Phoenix

Here is the info for USDA Zone 9b.

Average Date of Last Frost (spring)	February 15
Average Date of First Frost (fall)	December 15
Lowest Expected Low	25°F
Highest Expected Low	30°F

This means that on a really cold year, the coldest it will get is 25°F. On most years you should be prepared to experience lows near 30°F.

Plants to Grow in Phoenix

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