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.

The first opportunity to plant lobelia in Boulder can be estimated by looking at the USDA zone info.

Planting Calendar for Lobelia

Frost tolerance for lobelia:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Lobelia do well in quite a bit of cold which means that you can plant them quite a bit earlier in the year than more sensitive plants.

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

Last Frost Date

On average the last frost when the weather gets warmer is on April 15 in Boulder. In the coldest months of winter you can expect an average low temperature of -15°F.

Keep in mind that USDA zone info for Boulder is an average and the actual date of last frost will vary 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 lobelia 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.