The USDA Zone info is a great tool for gardeners to help us estimate your gardening schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

In Helena you can determine when to plant cleome by checking out the USDA zone info.

Planting Calendar for Cleome

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

It's probably not a good idea to plant cleome until after all chance of frost has passed because they are not cold tolerant.

The earliest that you can plant cleome 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 cleome and expect a good harvest is probably August. If you wait any later than that and your cleome may not have a chance to really do well. You can get started a few weeks earlier by starting your cleome indoors.

Last Frost Date

The average date of last frost is May 15 in Helena. It might get as low as -25°F during the coldest months of winter.

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 changes from year to year. Half of the time in Helena last frost occurs after May 15 so make sure that you are prepared to protect your cleome 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.