Before planting it is a good idea to find your USDA Zone info to figure out your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

By referring to the USDA zone info for Helena it's possible to figure out when it's a good idea to plant alternaria.

Planting Calendar for Alternaria

Frost tolerance for alternaria:	Not tolerant of frost.
When to plant:	After the last frost when the weather gets warmer.

You should not plant alternaria until after the last frost has passed because they are not cold tolerant.

The earliest that you can plant alternaria 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 alternaria and expect a good harvest is probably August. You probably don't want to wait any later than that or else your alternaria may not have a chance to grow to maturity. Starting your alternaria indoors is a great way to get them started a couple of 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 should expect an average low temperature of -25°F.

Since the USDA zone info for Helena is not always accurate the actual date of last frost can change quite a bit from year to year. Since half of the time in Helena you get surprised by a frost after May 15 be ready to cover your alternaria in the event of one of those late frosts.

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.