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.

You should be able to figure out when to plant helianthemum by using the USDA zone info for Riverside.

Planting Calendar for Helianthemum

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

Since helianthemum are one of those plants that can tolerate a little bit of cold weather you can plant them just a bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant helianthemum in Riverside 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. You probably don't want to wait any later than that or else your helianthemum may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your helianthemum indoors.

Last Frost Date

In Riverside the average date of last frost happens on February 15. You can expect an average low temperature of 25°F in the coldest months of winter.

Since the USDA zone info for Riverside may not be accurate from year to year the actual date of last frost changes from year to year. Since half of the time in Riverside there is a last frost after February 15 be ready to cover your helianthemum if you have a surprise late frost.

USDA Zone Info for Riverside

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 Riverside

You may be interested in your other planting guides for Riverside.