Before planting it is a good idea to find your USDA Zone info to estimate your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

One way of figuring out when it's possible to plant onions is to use the USDA zone info for Phoenix.

Planting Calendar for Onions

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

Onions do ok in pretty solid cold which means that you can plant them quite a bit earlier in the year than other plants that might not handle the cold.

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

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

Last Frost Date

On average all chance of frost has passed is on February 15 in Phoenix. You can expect an average low temperature of 25°F in 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 Phoenix and it changes from year to year. Half of the time in Phoenix it frosts late in the year after February 15 so be sure to be ready to protect your onions in the event of a surprise late frost.

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.