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

In Harlan you can determine when you can plant periwinkles by using the USDA zone info.

Planting Calendar for Periwinkles

Frost tolerance for periwinkles:	Not tolerant of frost.
When to plant:	After the last frost.

Since periwinkles are not cold tolerant you really should wait until after the last frost before you can plant them.

The earliest that you can plant periwinkles in Harlan 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. You can get started a few weeks earlier by starting your periwinkles indoors.

Last Frost Date

The average date of last frost is April 15 in Harlan. In the coldest months of winter you should expect an average low temperature of -20°F.

Since the USDA zone info for Harlan is an average the actual date of last frost is different every year. Half of the time in Harlan you get surprised by a frost after April 15 so make sure that you are ready to cover your periwinkles if you have one of those late frosts.

USDA Zone Info for Harlan

Here is the info for USDA Zone 5a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-20°F
Highest Expected Low	-15°F

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

Plants to Grow in Harlan

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