One of the first steps you take when you are determining 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.

It's possible to estimate when it's possible to plant trifolium by checking out the USDA zone info for Washington.

Planting Calendar for Trifolium

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

Trifolium are barely cold tolerant which tells us that you can plant them slightly earlier than more sensitive plants.

The earliest that you can plant trifolium in Washington 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 trifolium and expect a good harvest is probably August. If you wait any later than that and your trifolium may not have a chance to grow to maturity. You can get started a couple of weeks earlier by starting your trifolium indoors.

Last Frost Date

On average the last frost when the weather gets warmer is on April 15 in Washington. In the coldest months of winter you should expect an average low temperature of -10°F.

Since the USDA zone info for Washington may not be accurate from year to year the actual date of last frost changes from year to year. Half of the time in Washington you get a frost after April 15 so make sure that you are ready to cover your trifolium in the event of one of those late frosts.

USDA Zone Info for Washington

Here is the info for USDA Zone 6a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	-10°F
Highest Expected Low	-5°F

This means that on a really cold year, the coldest it will get is -10°F. On most years you should be prepared to experience lows near -5°F.

Plants to Grow in Washington

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