Before planting it is a good idea to find your USDA Zone info to estimate 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.

By using the USDA zone info for Helena it's possible to estimate when you can plant oenothera.

Planting Calendar for Oenothera

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

You can plant oenothera a bit earlier in the year because they do well in moderate cold.

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

The last month that you can plant oenothera and expect a good harvest is probably September. Any later than that and your oenothera may not have a chance to really do well. You can get started a couple of weeks earlier by starting your oenothera indoors.

Last Frost Date

The average date of last frost is March 15 in Helena. It might get as low as 10°F during the coldest months of winter.

Since the USDA zone info for Helena may not be accurate from year to year the actual date of last frost will vary from year to year. Half of the time in Helena it frosts late in the year after March 15 so make sure that you are ready to cover your oenothera if you have 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.