The USDA Zone info is a great tool for gardeners to help us figure out your gardening schedule. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

A way of estimating when it's a good idea to plant helianthemum is to consult 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.

Since helianthemum are one of those plants that can tolerate a little bit of cold weather you can plant them a little earlier in the year than other plants that might not handle the cold.

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 grow to maturity. You can get started a little bit earlier by starting your helianthemum indoors.

Last Frost Date

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

Keep in mind that USDA zone info for Watertown is an average and the actual date of last frost can change quite a bit from year to year. Since half of the time in Watertown there is a last frost after May 15 be ready to cover your helianthemum in the event of a late frost.

USDA Zone Info for Watertown

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 Watertown

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