One of the best tools that you have as gardeners to help us determine 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 Watertown should be reviewed to figure out when to plant tree onions.

Planting Calendar for Tree onions

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

Tree onions do ok in moderate cold which means that you can get them planted just a bit earlier than plants that are more sensitive to the cold.

The earliest that you can plant tree onions in Watertown is April. However, you really should wait until May if you don't want to take any chances.

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

Last Frost Date

On average the last frost is on May 15 in Watertown. You should expect an average low temperature of -25°F in the coldest months of winter.

Keep in mind that the actual date of last frost is an average because it is based on the USDA zone info for Watertown and it is different every year. Since half of the time in Watertown it frosts late in the year after May 15 be ready to cover your tree onions if you have a surprise 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.