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 best time to plant periwinkles in Seattle should be estimated by looking at the USDA zone info.

Planting Calendar for Periwinkles

Frost tolerance for periwinkles:	Not tolerant of frost.
When to plant:	After all chance of frost has passed.

Periwinkles do not do well in cold weather which tells us that you really should wait until it warms up after the last frost before you can plant them.

The earliest that you can plant periwinkles in Seattle is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant periwinkles and expect a good harvest is probably August. You probably don't want to wait any later than that or else your periwinkles may not have a chance to fully mature. Starting your periwinkles indoors is a great way to get them started a few weeks earlier.

Last Frost Date

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

Since the USDA zone info for Seattle is just an average the actual date of last frost is different every year. Since half of the time in Seattle there is a last frost after March 15 be ready to cover your periwinkles if you have a surprise late frost.

USDA Zone Info for Seattle

Here is the info for USDA Zone 8b.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	15°F
Highest Expected Low	20°F

This means that on a really cold year, the coldest it will get is 15°F. On most years you should be prepared to experience lows near 20°F.

Plants to Grow in Seattle

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