One of the first steps you take when you are determining your gardening schedule is find your USDA Zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

By using the USDA zone info for Boulder it's possible to estimate when it's a good idea to plant nierembergia.

Planting Calendar for Nierembergia

Frost tolerance for nierembergia:	Not tolerant of frost.
When to plant:	After all chance of frost has passed.

Since nierembergia are not cold tolerant it is necessary to wait until after all chance of frost has passed before you can plant them.

The earliest that you can plant nierembergia in Boulder is April. However, you really should wait until May if you don't want to take any chances.

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

Last Frost Date

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

Since the USDA zone info for Boulder is just an average the actual date of last frost will vary from year to year. Since half of the time in Boulder you get a frost after April 15 be ready to cover your nierembergia if you have a surprise 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.