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.

It's a good idea to determine when it's a good idea to plant astilbe by using the USDA zone info for Zone 4b.

Planting Calendar for Astilbe

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

Since astilbe do ok in moderate cold you can plant them a bit earlier in the year than other frost tender plants.

The earliest that you can plant astilbe in Zone 4b 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 astilbe and expect a good harvest is probably August. If you wait any later than that and your astilbe may not have a chance to grow to maturity. You can get started a little bit earlier by starting your astilbe indoors.

Last Frost Date

On average the last frost has passed is on May 15 in Zone 4b. You should expect an average low temperature of -25°F in the coldest months of winter.

Remember that USDA zone info for Zone 4b is not always accurate and the actual date of last frost is different every year. Since half of the time in Zone 4b last frost occurs after May 15 be ready to protect your astilbe if you have a surprise late frost.

USDA Zone Info for Zone 4b

Here is the info for USDA Zone 4b.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-25°F
Highest Expected Low	-20°F

This means that on a really cold year, the coldest it will get is -25°F. On most years you should be prepared to experience lows near -20°F.

Plants to Grow in Zone 4b

You may be interested in your other planting guides for Zone 4b.