Before planting it is a good idea to find your USDA Zone info to figure out your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

A way of estimating when it's a good idea to plant dahlias is to examine the USDA zone info for Billings.

Planting Calendar for Dahlias

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

It's probably not a good idea to plant dahlias until after the last frost when the weather gets warmer because they require warm weather.

The earliest that you can plant dahlias in Billings 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 grow to maturity. Starting your dahlias indoors is a great way to get them started a few weeks earlier.

Last Frost Date

In Billings the average date of last frost happens on May 15. You should expect an average low temperature of -25°F in the coldest months of winter.

Always keep in mind that the actual date of last frost is an average because it is based on the USDA zone info for Billings and it can change quite a bit from year to year. Since half of the time in Billings there is a last frost after May 15 be ready to cover your dahlias in the event of one of those late frosts.

USDA Zone Info for Billings

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 Billings

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