One of the best tools that you have as gardeners to help us determine 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.

In Colby you can figure out when you can plant sunflowers by looking at the USDA zone info.

Planting Calendar for Sunflowers

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

Since sunflowers require warm weather it's necessary to wait until after the last frost when the weather gets warmer before you can plant them.

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

Last Frost Date

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

Since the USDA zone info for Colby is just an average the actual date of last frost will vary from year to year. Since half of the time in Colby last frost occurs after April 15 be ready to cover your sunflowers if you have a late frost.

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.