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.

A way of estimating when it's possible to plant pennyroyal is to check out the USDA zone info for Philadelphia.

Planting Calendar for Pennyroyal

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

Pennyroyal are one of those plants that can tolerate quite a bit of cold weather which tells us that you can plant them much earlier than more sensitive plants.

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

The last month that you can plant pennyroyal and expect a good harvest is probably September. Any later than that and your pennyroyal may not have a chance to fully mature. You can get started a few weeks earlier by starting your pennyroyal indoors.

Last Frost Date

The average date of last frost is March 15 in Philadelphia. You should expect an average low temperature of 10°F in the coldest months of winter.

Since the USDA zone info for Philadelphia may not be accurate from year to year the actual date of last frost will vary from year to year. Since half of the time in Philadelphia you get surprised by a frost after March 15 be ready to cover your pennyroyal if you have one of those late frosts.

USDA Zone Info for Philadelphia

Here is the info for USDA Zone 8a.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	10°F
Highest Expected Low	15°F

This means that on a really cold year, the coldest it will get is 10°F. On most years you should be prepared to experience lows near 15°F.

Plants to Grow in Philadelphia

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