Before planting it is a good idea to find your USDA Zone info to figure out your garden schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

The USDA zone info for Helena should be looked at to estimate when it's the best time to plant calla lily.

Planting Calendar for Calla Lily

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

Since calla lily are not cold tolerant you must wait until after all chance of frost has passed before you can plant them.

The earliest that you can plant calla lily 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 calla lily and expect a good harvest is probably August. If you wait any later than that and your calla lily may not have a chance to fully mature. You can get started a few weeks earlier by starting your calla lily indoors.

Last Frost Date

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

Since the USDA zone info for Helena is just an average the actual date of last frost is different every year. Since half of the time in Helena you get a frost after May 15 be ready to cover your calla lily 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.