One of the first steps you take when you are getting a good idea 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 best time to plant dahlias in Helena should be figured out by using 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.

It's a bad idea to plant dahlias until after all chance of frost has passed because they require warm weather.

The earliest that you can plant dahlias in Helena is April. However, you really should wait until May 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 fully mature. You can get started a little bit earlier by starting your dahlias indoors.

Last Frost Date

On average the last frost is on March 15 in Helena. You should expect an average low temperature of 10°F in the coldest months of winter.

Since the USDA zone info for Helena is just an average the actual date of last frost can change quite a bit from year to year. Since half of the time in Helena you get a frost after March 15 be ready to cover your dahlias in the event of a surprise late frost.

USDA Zone Info for Helena

Here is the info for USDA Zone 8a.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	10°F
Highest Expected Low	15°F

This means that on a really cold year, the coldest it will get is 10°F. On most years you should be prepared to experience lows near 15°F.

Plants to Grow in Helena

You may be interested in your other planting guides for Helena.