One of the best tools that you have as gardeners to help us estimate 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 first opportunity to plant bells of ireland in Boulder can be figured out by using the USDA zone info.

Planting Calendar for Bells of Ireland

Frost tolerance for bells of ireland:	Tolerant of a very small amount of frost.
When to plant:	Up to 3 weeks before last frost.

Bells of Ireland are one of those plants that can tolerate a tiny bit of cold weather which tells us that you can plant them slightly earlier than other plants that might not handle the cold.

The earliest that you can plant bells of ireland in Boulder 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 bells of ireland and expect a good harvest is probably August. You probably don't want to wait any later than that or else your bells of ireland may not have a chance to fully mature. You can get started a couple of weeks earlier by starting your bells of ireland indoors.

Last Frost Date

In Boulder the average date of last frost happens on April 15. You should expect an average low temperature of -15°F in the coldest months of winter.

Since the USDA zone info for Boulder is not always accurate the actual date of last frost is different every year. Since half of the time in Boulder it frosts late in the year after April 15 be ready to cover your bells of ireland if you have a late frost.

USDA Zone Info for Boulder

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 Boulder

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