One of the first steps you take when you are estimating your gardening schedule is find your 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.

By checking out the USDA zone info for Helena you should be able to determine when it's possible to plant pentas.

Planting Calendar for Pentas

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

You should not plant pentas until after all chance of frost has passed because they are not cold tolerant.

The earliest that you can plant pentas 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 pentas and expect a good harvest is probably August. If you wait any later than that and your pentas may not have a chance to really do well. If you are starting your pentas 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.

It's important to remember that USDA zone info for Helena may not be accurate from year to year and the actual date of last frost changes from year to year. Since half of the time in Helena it frosts late in the year after May 15 be ready to protect your pentas in the event of 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.