Before planting it is a good idea to find your USDA Zone info to determine your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

The first chance to plant catharanthus in Helena can be determined by reviewing the USDA zone info.

Planting Calendar for Catharanthus

Frost tolerance for catharanthus:	Not tolerant of frost.
When to plant:	After the last frost has passed.

Catharanthus are not cold tolerant which tells us that it is important to wait until it warms up after the last frost before you can plant them.

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

The last month that you can plant catharanthus and expect a good harvest is probably August. Any later than that and your catharanthus may not have a chance to grow to maturity. Starting your catharanthus indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

The average date of last frost is March 15 in Helena. In the coldest months of winter you can expect an average low temperature of 10°F.

Keep in mind that the actual date of last frost may not be accurate from year to year 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 a frost after March 15 so make sure that you are ready to cover your catharanthus in the event of one of those late frosts.

USDA Zone Info for Helena

Here is the info for USDA Zone 8a.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	10°F
Highest Expected Low	15°F

This means that on a really cold year, the coldest it will get is 10°F. On most years you should be prepared to experience lows near 15°F.

Plants to Grow in Helena

You may be interested in your other planting guides for Helena.