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.

One way of determining when to plant helianthemum is to use the USDA zone info for Watertown.

Planting Calendar for Helianthemum

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

You can plant helianthemum a bit earlier in the year because they are one of those plants that can tolerate a little bit of cold weather.

The earliest that you can plant helianthemum in Watertown 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. Starting your helianthemum indoors is a great way to get them started a little bit earlier.

Last Frost Date

On average the last frost is on May 15 in Watertown. You can expect an average low temperature of -30°F in the coldest months of winter.

Since the USDA zone info for Watertown is just an average the actual date of last frost changes from year to year. Half of the time in Watertown last frost occurs after May 15 so make sure that you are prepared to protect your helianthemum in the event of a surprise late frost.

USDA Zone Info for Watertown

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 Watertown

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