One of the first steps you take when you are estimating your gardening schedule is find your 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.

The USDA zone info for Helena can be read to estimate when it's a good idea to plant four o' clock.

Planting Calendar for Four O' Clock

Frost tolerance for four o' clock:	Not tolerant of frost.
When to plant:	After the last frost has passed.

It's not a good idea to plant four o' clock until after the last frost when the weather gets warmer because they are not cold tolerant.

The earliest that you can plant four o' clock 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 four o' clock and expect a good harvest is probably August. If you wait any later than that and your four o' clock may not have a chance to grow to maturity. Starting your four o' clock indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

In Helena the average date of last frost happens on May 15. It might get as low as -25°F during the coldest months of winter.

Since the USDA zone info for Helena is not always accurate the actual date of last frost changes from year to year. Since half of the time in Helena there is a last frost after May 15 be ready to cover your four o' clock in the event of 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.