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

In Helena you can estimate when it's possible to plant argyranthemum by reviewing the USDA zone info.

Planting Calendar for Argyranthemum

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

Since argyranthemum require warm weather it's necessary to wait until after all chance of frost has passed before you can plant them.

The earliest that you can plant argyranthemum 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 argyranthemum and expect a good harvest is probably August. Any later than that and your argyranthemum may not have a chance to really do well. If you are starting your argyranthemum 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 just an average the actual date of last frost can change quite a bit from year to year. Half of the time in Helena last frost occurs after May 15 so just be sure to be ready to cover your argyranthemum in the event of a surprise 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.