One of the first steps you take when you are figuring out your gardening schedule is find your 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.

The best time to plant astilbe in Zone 4a can be determined by looking at the USDA zone info.

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 are barely cold tolerant you can plant them slightly earlier in the year than other plants that might not handle the cold.

The earliest that you can plant astilbe in Zone 4a 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 fully mature. You can get started a few weeks earlier by starting your astilbe indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on May 15 in Zone 4a. You can expect an average low temperature of -30°F in the coldest months of winter.

Since the USDA zone info for Zone 4a is an average the actual date of last frost changes from year to year. Since half of the time in Zone 4a last frost occurs after May 15 be ready to cover your astilbe if you have a surprise late frost.

USDA Zone Info for Zone 4a

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°F

This means that on a really cold year, the coldest it will get is -30°F. On most years you should be prepared to experience lows near -25°F.

Plants to Grow in Zone 4a

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