One of the first steps you take when you are determining your gardening schedule is find your USDA Zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

The USDA zone info for Helena should be reviewed to figure out when it's possible to plant arabis.

Planting Calendar for Arabis

Frost tolerance for arabis:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Arabis are very cold tolerant which means that you can get them planted much earlier than more sensitive plants.

The earliest that you can plant arabis in Helena is March. However, you really should wait until April if you don't want to take any chances.

The last month that you can plant arabis and expect a good harvest is probably August. If you wait any later than that and your arabis may not have a chance to really do well. Starting your arabis 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. It might get as low as -25°F during the coldest months of winter.

It's important to remember that USDA zone info for Helena is an average and the actual date of last frost can change quite a bit from year to year. Half of the time in Helena there is a last frost after May 15 so always be ready to cover your arabis if you have 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.