One of the best tools that you have as gardeners to help us figure out your gardening schedule is the USDA zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

The USDA zone info for Napa can be used to figure out when it's the best time to plant hardy asters.

Planting Calendar for Hardy Asters

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

Since hardy asters do ok in moderate cold you can plant them a bit earlier in the year than more sensitive plants.

The earliest that you can plant hardy asters in Napa 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 hardy asters and expect a good harvest is probably September. Any later than that and your hardy asters may not have a chance to grow to maturity. Starting your hardy asters indoors is a great way to get them started a little bit earlier.

Last Frost Date

On average the last frost is on February 15 in Napa. In the coldest months of winter you can expect an average low temperature of 25°F.

Since the USDA zone info for Napa is not always accurate the actual date of last frost changes from year to year. Half of the time in Napa there is a last frost after February 15 so make sure that you are ready to cover your hardy asters in the event of one of those late frosts.

USDA Zone Info for Napa

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 Napa

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