One of the best tools that you have as gardeners to help us estimate your gardening schedule is the USDA zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

A common way of estimating when to plant lithospermum is to consult the USDA zone info for Colby.

Planting Calendar for Lithospermum

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

It's probably a bad idea to plant lithospermum until after the last frost because they are not cold tolerant.

The earliest that you can plant lithospermum in Colby 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. If you wait any later than that and your lithospermum may not have a chance to grow to maturity. Starting your lithospermum indoors is a great way to get them started a little bit earlier.

Last Frost Date

On average the last frost is on April 15 in Colby. It might get as low as -15°F during the coldest months of winter.

Since the USDA zone info for Colby may not be accurate from year to year the actual date of last frost is different every year. Half of the time in Colby last frost occurs after April 15 so always be ready to protect your lithospermum if you have one of those late frosts.

USDA Zone Info for Colby

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 Colby

You may be interested in your other planting guides for Colby.