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

The first chance to plant primula in Portola Valley should be determined by reviewing the USDA zone info.

Planting Calendar for Primula

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

Primula can survive in pretty solid cold which tells us that you can plant them much earlier in the year than more sensitive plants.

The earliest that you can plant primula in Portola Valley 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 primula and expect a good harvest is probably October. You probably don't want to wait any later than that or else your primula may not have a chance to fully mature. If you are starting your primula indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

On average the last frost when the weather gets warmer is on January 31 in Portola Valley. You can 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 can change quite a bit from year to year. Since half of the time in Portola Valley you get surprised by a frost after January 31 be ready to cover your primula in the event of a late frost.

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.