One of the best tools that you have as gardeners to help us determine your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

By using the USDA zone info for Helena it's possible to estimate when it's the best time to plant sweet williams.

Planting Calendar for Sweet Williams

Frost tolerance for sweet williams:	Tolerant of some frost.
When to plant:	Up to 5 weeks before last frost.

You can plant sweet williams a bit earlier in the year because they are moderately cold tolerant.

The earliest that you can plant sweet williams in Helena is March. However, you really should wait until April if you don't want to take any chances.

The last month that you can plant sweet williams and expect a good harvest is probably August. Any later than that and your sweet williams may not have a chance to fully mature. You can get started a couple of weeks earlier by starting your sweet williams indoors.

Last Frost Date

In Helena 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.

Since the USDA zone info for Helena is not always accurate the actual date of last frost is different every year. Half of the time in Helena you get a frost after May 15 so always be ready to protect your sweet williams in the event of one of those late frosts.

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.