One of the first steps you take when you are figuring out your gardening schedule is find your 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.

In Mercer Island you can figure out when it's a good idea to plant bunching onions by looking at the USDA zone info.

Planting Calendar for Bunching Onions

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

Since bunching onions do ok in moderate cold you can plant them slightly earlier in the year than plants that are more sensitive to the cold.

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

Last Frost Date

The average date of last frost is March 15 in Mercer Island. In the coldest months of winter you can expect an average low temperature of 15°F.

Since the USDA zone info for Mercer Island may not be accurate from year to year the actual date of last frost is different every year. Half of the time in Mercer Island you get surprised by a frost after March 15 so make sure that you are prepared to cover your bunching onions in the event of a surprise late frost.

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.