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 looking at the USDA zone info for Stillwater you should be able to figure out when you can plant helianthemum.

Planting Calendar for Helianthemum

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

Since helianthemum do well in moderate cold you can plant them just a bit earlier in the year than other plants that might not handle the cold.

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

The last month that you can plant helianthemum and expect a good harvest is probably August. Any later than that and your helianthemum may not have a chance to fully mature. If you are starting your helianthemum indoors then you might be able to get away with starting them a little bit earlier.

Last Frost Date

In Stillwater the average date of last frost happens on May 15. You can expect an average low temperature of -25°F in the coldest months of winter.

Keep in mind that USDA zone info for Stillwater is an average and the actual date of last frost changes from year to year. Since half of the time in Stillwater it frosts late in the year after May 15 be ready to protect your helianthemum if you have a late frost.

USDA Zone Info for Stillwater

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 Stillwater

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