One of the best tools that you have as gardeners to help us figure out your gardening schedule is the 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 Portola Valley can be read to estimate when to plant pearl onions.

Planting Calendar for Pearl onions

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

Pearl onions can survive in some cold which tells us that 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 pearl onions in Portola Valley 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 pearl onions and expect a good harvest is probably September. You probably don't want to wait any later than that or else your pearl onions may not have a chance to really do well. You can get started a couple of weeks earlier by starting your pearl onions indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on January 31 in Portola Valley. You should expect an average low temperature of 30°F in the coldest months of winter.

Since the USDA zone info for Portola Valley is just an average the actual date of last frost will vary from year to year. Since half of the time in Portola Valley it frosts late in the year after January 31 be ready to cover your pearl onions in the event of one of those late frosts.

USDA Zone Info for Portola Valley

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 Portola Valley

You may be interested in your other planting guides for Portola Valley.