Before planting it is a good idea to find your USDA Zone info to estimate your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

The USDA zone info for Boulder should be reffered to in order to determine when to plant daylily.

Planting Calendar for Daylily

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

Daylily are moderately cold tolerant which tells us that you can start planting them earlier than plants that are more sensitive to the cold.

The earliest that you can plant daylily 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 daylily and expect a good harvest is probably September. If you wait any later than that and your daylily may not have a chance to grow to maturity. If you are starting your daylily indoors then you might be able to get away with starting them a little bit earlier.

Last Frost Date

The average date of last frost is April 15 in Boulder. You can 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 daylily 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.