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.

A way of figuring out when you can plant alternaria is to look at the USDA zone info for Helena.

Planting Calendar for Alternaria

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

Alternaria do not do well in cold weather which tells us that it's necessary to wait until it warms up after all chance of frost has passed before you can plant them.

The earliest that you can plant alternaria in Helena is April. However, you really should wait until May 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. If you wait any later than that and your alternaria may not have a chance to fully mature. You can get started a little bit earlier by starting your alternaria indoors.

Last Frost Date

In Helena the average date of last frost happens on March 15. It might get as low as 10°F during the coldest months of winter.

Since the USDA zone info for Helena may not be accurate from year to year the actual date of last frost is different every year. Since half of the time in Helena there is a last frost after March 15 be ready to cover your alternaria if you have a surprise late frost.

USDA Zone Info for Helena

Here is the info for USDA Zone 8a.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	10°F
Highest Expected Low	15°F

This means that on a really cold year, the coldest it will get is 10°F. On most years you should be prepared to experience lows near 15°F.

Plants to Grow in Helena

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