One of the first steps you take when you are making a decision about 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.

The USDA zone info for Costa Mesa can be reviewed to figure out when it's the best time to plant onions.

Planting Calendar for Onions

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

Onions are one of those plants that can tolerate quite a bit of cold weather which means that you can start planting them much earlier than other plants that might not handle the cold.

The earliest that you can plant onions in Costa Mesa 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. If you wait any later than that and your onions may not have a chance to really do well. Starting your onions indoors is a great way to get them started a little bit earlier.

Last Frost Date

The average date of last frost is January 31 in Costa Mesa. In the coldest months of winter you can expect an average low temperature of 35°F.

Always keep in mind that the actual date of last frost is not always accurate because it is based on the USDA zone info for Costa Mesa and it is different every year. Half of the time in Costa Mesa you get a frost after January 31 so just be sure to be ready to cover your onions if you have one of those late frosts.

USDA Zone Info for Costa Mesa

Here is the info for USDA Zone 10b.

Average Date of Last Frost (spring)	January 31
Average Date of First Frost (fall)	December 15
Lowest Expected Low	35°F
Highest Expected Low	40°F

This means that on a really cold year, the coldest it will get is 35°F. On most years you should be prepared to experience lows near 40°F.

Plants to Grow in Costa Mesa

You may be interested in your other planting guides for Costa Mesa.