One of the best tools that you have as gardeners to help us figure out your gardening schedule is the USDA zone info. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

By looking at the USDA zone info for Mercer Island you should be able to figure out when it's possible to plant sweet williams.

Planting Calendar for Sweet Williams

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

Sweet Williams tend to make it in mild cold which tells us that you can plant them just a bit earlier in the year than plants that are more sensitive to the cold.

The earliest that you can plant sweet williams in Mercer Island is February. However, you really should wait until March if you don't want to take any chances.

The last month that you can plant sweet williams and expect a good harvest is probably September. You probably don't want to wait any later than that or else your sweet williams may not have a chance to fully mature. If you are starting your sweet williams indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

The average date of last frost is March 15 in Mercer Island. It might get as low as 15°F during the coldest months of winter.

Just be sure to remember that the actual date of last frost is just an average because it is based on the USDA zone info for Mercer Island and it changes from year to year. Since half of the time in Mercer Island last frost occurs after March 15 be ready to cover your sweet williams in the event of one of those late frosts.

USDA Zone Info for Mercer Island

Here is the info for USDA Zone 8b.

Average Date of Last Frost (spring)	March 15
Average Date of First Frost (fall)	November 15
Lowest Expected Low	15°F
Highest Expected Low	20°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 20°F.

Plants to Grow in Mercer Island

You may be interested in your other planting guides for Mercer Island.