One of the best tools that you have as gardeners to help us estimate 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.

The USDA zone info for Williston can be reffered to in order to estimate when to plant helianthemum.

Planting Calendar for Helianthemum

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

Helianthemum are one of those plants that can tolerate a little bit of cold weather which tells us that you can plant them a little bit earlier than more sensitive plants.

The earliest that you can plant helianthemum in Williston 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. If you wait any later than that and your helianthemum may not have a chance to really do well. Starting your helianthemum indoors is a great way to get them started a little bit earlier.

Last Frost Date

The average date of last frost is May 15 in Williston. In the coldest months of winter you can expect an average low temperature of -30°F.

Since the USDA zone info for Williston may not be accurate from year to year the actual date of last frost is different every year. Half of the time in Williston last frost occurs after May 15 so be sure to be ready to protect your helianthemum in the event of a surprise late frost.

USDA Zone Info for Williston

Here is the info for USDA Zone 4a.

Average Date of Last Frost (spring)	May 15
Average Date of First Frost (fall)	September 15
Lowest Expected Low	-30°F
Highest Expected Low	-25°F

This means that on a really cold year, the coldest it will get is -30°F. On most years you should be prepared to experience lows near -25°F.

Plants to Grow in Williston

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