Before planting it is a good idea to find your USDA Zone info to estimate your garden schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

You can determine when it's a good idea to plant centaurea in Boulder by using the USDA zone info.

Planting Calendar for Centaurea

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

You can plant centaurea just a bit earlier in the year because they are one of those plants that can tolerate a little bit of cold weather.

The earliest that you can plant centaurea in Boulder 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 centaurea and expect a good harvest is probably September. Any later than that and your centaurea may not have a chance to really do well. Starting your centaurea indoors is a great way to get them started a little bit earlier.

Last Frost Date

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

Since the USDA zone info for Boulder may not be accurate from year to year 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 protect your centaurea in the event of 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.