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 USDA zone info for Casper should be read to estimate when it's the best time to plant periwinkles.

Planting Calendar for Periwinkles

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

You can not plant periwinkles until after the last frost when the weather gets warmer because they do not do well in cold weather.

The earliest that you can plant periwinkles in Casper 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. Any later than that and your periwinkles may not have a chance to fully mature. You can get started a little bit earlier by starting your periwinkles indoors.

Last Frost Date

On average the last frost is on April 15 in Casper. It might get as low as -20°F during the coldest months of winter.

Always keep in mind that USDA zone info for Casper is an average and the actual date of last frost will vary from year to year. Half of the time in Casper you get a frost after April 15 so make sure that you are prepared to protect your periwinkles if you have a surprise late frost.

USDA Zone Info for Casper

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 Casper

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