One of the first steps you take when you are estimating your gardening schedule is find your USDA Zone info. 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 lithospermum in Boulder can be figured out by referring to the USDA zone info.

Planting Calendar for Lithospermum

Frost tolerance for lithospermum:	Not tolerant of frost.
When to plant:	After the last frost has passed.

It's not a good idea to plant lithospermum until after all chance of frost has passed because they require warm weather.

The earliest that you can plant lithospermum in Boulder is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant lithospermum and expect a good harvest is probably August. Any later than that and your lithospermum may not have a chance to fully mature. You can get started a few weeks earlier by starting your lithospermum indoors.

Last Frost Date

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

It's important to remember that the actual date of last frost is not always accurate because it is based on the USDA zone info for Boulder and it is different every year. Half of the time in Boulder last frost occurs after April 15 so make sure that you are ready to protect your lithospermum if you have 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.