The USDA Zone info is a great tool for gardeners to help us determine 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.

You should be able to estimate when it's the best time to plant cosmos by using the USDA zone info for Somersworth.

Planting Calendar for Cosmos

Frost tolerance for cosmos:	Tolerant of a very small amount of frost.
When to plant:	Up to 3 weeks before last frost.

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

The earliest that you can plant cosmos in Somersworth 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 cosmos and expect a good harvest is probably August. Any later than that and your cosmos may not have a chance to grow to maturity. If you are starting your cosmos indoors then you might be able to get away with starting them a couple of weeks earlier.

Last Frost Date

In Somersworth the average date of last frost happens on April 15. In the coldest months of winter you can expect an average low temperature of -15°F.

Since the USDA zone info for Somersworth is just an average the actual date of last frost is different every year. Half of the time in Somersworth it frosts late in the year after April 15 so make sure that you are ready to protect your cosmos if you have one of those late frosts.

USDA Zone Info for Somersworth

Here is the info for USDA Zone 5b.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-15°F
Highest Expected Low	-10°F

This means that on a really cold year, the coldest it will get is -15°F. On most years you should be prepared to experience lows near -10°F.

Plants to Grow in Somersworth

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