Before planting it is a good idea to find your USDA Zone info to determine your garden schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

By looking at the USDA zone info for Helena you should be able to estimate when it's possible to plant iberis.

Planting Calendar for Iberis

Frost tolerance for iberis:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

Iberis do ok in mild cold which tells us that you can plant them a little earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant iberis 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 iberis and expect a good harvest is probably August. Any later than that and your iberis may not have a chance to really do well. If you are starting your iberis indoors then you might be able to get away with starting them a couple of weeks earlier.

Last Frost Date

On average the last frost is on May 15 in Helena. You should expect an average low temperature of -25°F in the coldest months of winter.

Always keep in mind that USDA zone info for Helena is not always accurate and the actual date of last frost will vary from year to year. Since half of the time in Helena it frosts late in the year after May 15 be ready to cover your iberis 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.