One of the best tools that you have as gardeners to help us determine 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.

It's possible to estimate when it's the best time to plant zinnia by checking out the USDA zone info for Great Falls.

Planting Calendar for Zinnia

Frost tolerance for zinnia:	Not tolerant of frost.
When to plant:	After the last frost.

Since zinnia are not cold tolerant you must wait until after the last frost has passed before you can plant them.

The earliest that you can plant zinnia in Great Falls 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 zinnia and expect a good harvest is probably August. If you wait any later than that and your zinnia may not have a chance to grow to maturity. You can get started a few weeks earlier by starting your zinnia indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on May 15 in Great Falls. You should expect an average low temperature of -30°F in the coldest months of winter.

Since the USDA zone info for Great Falls is an average the actual date of last frost will vary from year to year. Since half of the time in Great Falls last frost occurs after May 15 be ready to protect your zinnia in the event of a late frost.

USDA Zone Info for Great Falls

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°F

This means that on a really cold year, the coldest it will get is -30°F. On most years you should be prepared to experience lows near -25°F.

Plants to Grow in Great Falls

You may be interested in your other planting guides for Great Falls.