One of the best tools that you have as gardeners to help us figure out your gardening schedule is the USDA zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

In Helena you can figure out when it's a good idea to plant calendula by reviewing the USDA zone info.

Planting Calendar for Calendula

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

Calendula can survive in mild cold which means that you can plant them just a bit earlier in the year than more sensitive plants.

The earliest that you can plant calendula 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 calendula and expect a good harvest is probably August. You probably don't want to wait any later than that or else your calendula may not have a chance to fully mature. If you are starting your calendula 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. You should expect an average low temperature of -25°F in the coldest months of winter.

Keep in mind that USDA zone info for Helena may not be accurate from year to year and the actual date of last frost is different every year. Half of the time in Helena there is a last frost after May 15 so just be sure to be ready to cover your calendula 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.