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

A way of making a decision about when it's a good idea to plant trailing portulaca is to check out the USDA zone info for Helena.

Planting Calendar for Trailing Portulaca

Frost tolerance for trailing portulaca:	Not tolerant of frost.
When to plant:	After the last frost.

It's not a good idea to plant trailing portulaca until after the last frost has passed because they are not cold tolerant.

The earliest that you can plant trailing portulaca 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 trailing portulaca and expect a good harvest is probably August. Any later than that and your trailing portulaca may not have a chance to fully mature. Starting your trailing portulaca indoors is a great way to get them started a couple of weeks earlier.

Last Frost Date

The average date of last frost is May 15 in Helena. In the coldest months of winter you should expect an average low temperature of -25°F.

It's important to remember that the actual date of last frost is an average because it is based on the USDA zone info for Helena and it can change quite a bit from year to year. Half of the time in Helena it frosts late in the year after May 15 so make sure that you are prepared to cover your trailing portulaca 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.