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.

One way of making a decision about when it's a good idea to plant penstemon is to refer to the USDA zone info for Rock Falls.

Planting Calendar for Penstemon

Frost tolerance for penstemon:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

Penstemon do well in mild cold which tells us that you can plant them just a bit earlier in the year than other frost tender plants.

The earliest that you can plant penstemon in Rock Falls 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 penstemon and expect a good harvest is probably September. You probably don't want to wait any later than that or else your penstemon may not have a chance to really do well. You can get started a little bit earlier by starting your penstemon indoors.

Last Frost Date

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

Since the USDA zone info for Rock Falls is just an average the actual date of last frost will vary from year to year. Half of the time in Rock Falls you get surprised by a frost after April 15 so make sure that you are prepared to cover your penstemon if you have one of those late frosts.

USDA Zone Info for Rock Falls

Here is the info for USDA Zone 5b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-15°F
Highest Expected Low	-10°F

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

Plants to Grow in Rock Falls

You may be interested in your other planting guides for Rock Falls.