The USDA Zone info is a great tool for gardeners to help us figure out your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

You should be able to figure out when it's the best time to plant ageratum by referring to the USDA zone info for Havre.

Planting Calendar for Ageratum

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

Ageratum do not do well in cold weather which tells us that it's necessary to wait until it warms up after the last frost before you can plant them.

The earliest that you can plant ageratum in Havre is May. However, you really should wait until June if you don't want to take any chances.

The last month that you can plant ageratum and expect a good harvest is probably August. Any later than that and your ageratum may not have a chance to grow to maturity. Starting your ageratum indoors is a great way to get them started a little bit earlier.

Last Frost Date

On average the last frost has passed is on May 15 in Havre. In the coldest months of winter you should expect an average low temperature of -30°F.

It's important to remember that the actual date of last frost is not always accurate because it is based on the USDA zone info for Havre and it will vary from year to year. Half of the time in Havre there is a last frost after May 15 so always be ready to cover your ageratum if you have one of those late frosts.

USDA Zone Info for Havre

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 Havre

You may be interested in your other planting guides for Havre.