One of the first steps you take when you are estimating 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 Portola Valley can be used to figure out when to plant helianthemum.

Planting Calendar for Helianthemum

Frost tolerance for helianthemum:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

Helianthemum are moderately cold tolerant which means that you can start planting them earlier than other frost tender plants.

The earliest that you can plant helianthemum 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 helianthemum and expect a good harvest is probably October. If you wait any later than that and your helianthemum may not have a chance to fully mature. You can get started a couple of weeks earlier by starting your helianthemum indoors.

Last Frost Date

The average date of last frost is January 31 in Portola Valley. In the coldest months of winter you should expect an average low temperature of 30°F.

Since the USDA zone info for Portola Valley is an average the actual date of last frost is different every year. Since half of the time in Portola Valley you get a frost after January 31 be ready to protect your helianthemum if you have 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.