The USDA Zone info is a great tool for gardeners to help us determine your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

The earliest that you can plant oenothera in Boulder can be determined by referring to the USDA zone info.

Planting Calendar for Oenothera

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

Oenothera do well in moderate cold which means that you can get them planted earlier than other plants that might not handle the cold.

The earliest that you can plant oenothera 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 oenothera and expect a good harvest is probably September. Any later than that and your oenothera may not have a chance to grow to maturity. You can get started a few weeks earlier by starting your oenothera indoors.

Last Frost Date

On average all chance of frost has passed is on April 15 in Boulder. In the coldest months of winter you should expect an average low temperature of -15°F.

Since the USDA zone info for Boulder may not be accurate from year to year the actual date of last frost changes from year to year. Since half of the time in Boulder it frosts late in the year after April 15 be ready to protect your oenothera in the event of 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.