One of the best tools that you have as gardeners to help us figure out 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.

By reviewing the USDA zone info for Helena it's a good idea to figure out when you can plant chrysanthemum.

Planting Calendar for Chrysanthemum

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

It's probably a bad idea to plant chrysanthemum until after the last frost because they require warm weather.

The earliest that you can plant chrysanthemum in Helena 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 chrysanthemum and expect a good harvest is probably August. You probably don't want to wait any later than that or else your chrysanthemum may not have a chance to grow to maturity. If you are starting your chrysanthemum indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

On average the last frost has passed is on May 15 in Helena. In the coldest months of winter you can expect an average low temperature of -25°F.

Since the USDA zone info for Helena is an average the actual date of last frost is different every year. Half of the time in Helena you get a frost after May 15 so be sure to be ready to cover your chrysanthemum in the event of a late frost.

USDA Zone Info for Helena

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 Helena

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