One of the first steps you take when you are estimating 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.

You can figure out when you can plant dahlias in Helena by looking at the USDA zone info.

Planting Calendar for Dahlias

Frost tolerance for dahlias:	Not tolerant of frost.
When to plant:	After the last frost has passed.

Dahlias do not do well in cold weather which tells us that you have to wait until it warms up after the last frost before you can plant them.

The earliest that you can plant dahlias 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 dahlias and expect a good harvest is probably August. You probably don't want to wait any later than that or else your dahlias may not have a chance to really do well. You can get started a few weeks earlier by starting your dahlias indoors.

Last Frost Date

The average date of last frost is May 15 in Helena. In the coldest months of winter you can expect an average low temperature of -25°F.

It's important to remember that the actual date of last frost is just an average because it is based on the USDA zone info for Helena and it will vary from year to year. Half of the time in Helena it frosts late in the year after May 15 so be sure to be ready to cover your dahlias if you have a surprise 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.