One of the best tools that you have as gardeners to help us determine 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.

You can figure out when to plant periwinkles in Zone 4a by referring to 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.

You should not plant periwinkles until after the last frost has passed because they are not cold tolerant.

The earliest that you can plant periwinkles in Zone 4a is May. However, you really should wait until June 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. Any later than that and your periwinkles may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your periwinkles indoors.

Last Frost Date

In Zone 4a the average date of last frost happens on May 15. You should expect an average low temperature of -30°F in the coldest months of winter.

Just be sure to remember that the actual date of last frost is not always accurate because it is based on the USDA zone info for Zone 4a and it will vary from year to year. Half of the time in Zone 4a there is a last frost after May 15 so make sure that you are prepared to cover your periwinkles in the event of a late frost.

USDA Zone Info for Zone 4a

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°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 -25°F.

Plants to Grow in Zone 4a

You may be interested in your other planting guides for Zone 4a.