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.

By reviewing the USDA zone info for Helena it's a good idea to determine when it's possible to plant tithonia.

Planting Calendar for Tithonia

Frost tolerance for tithonia:	Not tolerant of frost.
When to plant:	After all chance of frost has passed.

Tithonia are not cold tolerant which means that it's necessary to wait until it warms up after the last frost has passed before you can plant them.

The earliest that you can plant tithonia 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 tithonia and expect a good harvest is probably August. You probably don't want to wait any later than that or else your tithonia may not have a chance to grow to maturity. If you are starting your tithonia indoors then you might be able to get away with starting them a couple of weeks earlier.

Last Frost Date

On average all chance of frost has passed is on May 15 in Helena. In the coldest months of winter you can expect an average low temperature of -25°F.

It's important to remember that the actual date of last frost is just an average because it is based on the USDA zone info for Helena and it will vary from year to year. Half of the time in Helena you get surprised by a frost after May 15 so be sure to be ready to protect your tithonia 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.