Before planting it is a good idea to find your USDA Zone info to figure out 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 can be looked at to determine when to plant iceberg lettuce.

Planting Calendar for Iceberg lettuce

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

You can plant iceberg lettuce a bit earlier in the year because they do ok in moderate cold.

The earliest that you can plant iceberg lettuce 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 iceberg lettuce and expect a good harvest is probably August. If you wait any later than that and your iceberg lettuce may not have a chance to grow to maturity. Starting your iceberg lettuce 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 can expect an average low temperature of -15°F in the coldest months of winter.

Remember that USDA zone info for Boulder is just an average and the actual date of last frost will vary from year to year. Half of the time in Boulder you get surprised by a frost after April 15 so always be ready to cover your iceberg lettuce if you have one of those late frosts.

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.