The USDA Zone info is a great tool for gardeners to help us determine your gardening schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

By looking at the USDA zone info for Grinnell it's possible to figure out when you can plant penstemon.

Planting Calendar for Penstemon

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

Since penstemon are one of those plants that can tolerate a little bit of cold weather you can plant them just a bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant penstemon in Grinnell 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. Any later than that and your penstemon may not have a chance to really do well. You can get started a few weeks earlier by starting your penstemon indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on April 15 in Grinnell. In the coldest months of winter you can expect an average low temperature of -20°F.

Since the USDA zone info for Grinnell is not always accurate the actual date of last frost changes from year to year. Half of the time in Grinnell you get a frost after April 15 so make sure that you are ready to protect your penstemon in the event of a late frost.

USDA Zone Info for Grinnell

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 Grinnell

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