One of the first steps you take when you are figuring out your gardening schedule is find your USDA Zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

The earliest that you can plant watercress in Mercer Island can be estimated by reviewing the USDA zone info.

Planting Calendar for Watercress

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

Since watercress do ok in moderate cold you can plant them a bit earlier in the year than other frost tender plants.

The earliest that you can plant watercress 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 watercress and expect a good harvest is probably August. Any later than that and your watercress may not have a chance to fully mature. You can get started a couple of weeks earlier by starting your watercress indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on March 15 in Mercer Island. In the coldest months of winter you can expect an average low temperature of 15°F.

Just be sure to remember that the actual date of last frost is not always accurate because it is based on the USDA zone info for Mercer Island and it will vary from year to year. Half of the time in Mercer Island last frost occurs after March 15 so make sure that you are prepared to cover your watercress 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.