One of the best tools that you have as gardeners to help us determine your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

A way of determining when to plant achillea is to examine the USDA zone info for Zone 4b.

Planting Calendar for Achillea

Frost tolerance for achillea:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Achillea tend to make it in cold weather which means that you can plant them quite a bit earlier in the year than other frost tender plants.

The earliest that you can plant achillea in Zone 4b 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 achillea and expect a good harvest is probably August. If you wait any later than that and your achillea may not have a chance to really do well. If you are starting your achillea indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

In Zone 4b the average date of last frost happens on May 15. In the coldest months of winter you should expect an average low temperature of -25°F.

It's important to remember that USDA zone info for Zone 4b is an average and the actual date of last frost is different every year. Half of the time in Zone 4b last frost occurs after May 15 so just be sure to be ready to cover your achillea if you have a 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.