The USDA Zone info is a great tool for gardeners to help us determine your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

A common way of estimating when to plant pennyroyal is to examine the USDA zone info for Zone 4a.

Planting Calendar for Pennyroyal

Frost tolerance for pennyroyal:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Since pennyroyal do well in cold you can plant them much earlier in the year than more sensitive plants.

The earliest that you can plant pennyroyal in Zone 4a is March. However, you really should wait until April if you don't want to take any chances.

The last month that you can plant pennyroyal and expect a good harvest is probably August. If you wait any later than that and your pennyroyal may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your pennyroyal indoors.

Last Frost Date

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

Keep in mind that USDA zone info for Zone 4a is an average and the actual date of last frost will vary from year to year. Since half of the time in Zone 4a you get a frost after May 15 be ready to cover your pennyroyal if you have a surprise 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.