The USDA Zone info is a great tool for gardeners to help us determine your gardening 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 Rock Falls should be reviewed to estimate when it's the best time to plant delphinium.

Planting Calendar for Delphinium

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

Since delphinium are barely cold tolerant you can plant them slightly earlier in the year than more sensitive plants.

The earliest that you can plant delphinium in Rock Falls 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 delphinium and expect a good harvest is probably August. If you wait any later than that and your delphinium may not have a chance to fully mature. Starting your delphinium indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

The average date of last frost is April 15 in Rock Falls. It might get as low as -15°F during the coldest months of winter.

Since the USDA zone info for Rock Falls is not always accurate the actual date of last frost changes from year to year. Since half of the time in Rock Falls you get a frost after April 15 be ready to cover your delphinium if you have a late frost.

USDA Zone Info for Rock Falls

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 Rock Falls

You may be interested in your other planting guides for Rock Falls.