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.

You should be able to estimate when you can plant purple rock cress by reviewing the USDA zone info for Helena.

Planting Calendar for Purple Rock Cress

Frost tolerance for purple rock cress:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Purple Rock Cress are very cold tolerant which tells us that you can plant them much earlier than plants that are more sensitive to the cold.

The earliest that you can plant purple rock cress 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 purple rock cress and expect a good harvest is probably September. Any later than that and your purple rock cress may not have a chance to grow to maturity. You can get started a little bit earlier by starting your purple rock cress indoors.

Last Frost Date

On average all chance of frost has passed is on March 15 in Helena. In the coldest months of winter you can expect an average low temperature of 10°F.

Since the USDA zone info for Helena may not be accurate from year to year the actual date of last frost changes from year to year. Since half of the time in Helena last frost occurs after March 15 be ready to protect your purple rock cress if you have a surprise late frost.

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.