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 referring to the USDA zone info for Washington it's a good idea to determine when it's a good idea to plant trifolium.

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 one of those plants that can tolerate a tiny bit of cold weather which means that you can plant them slightly earlier than other plants that might not handle the cold.

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. Any later than that and your trifolium may not have a chance to really do well. If you are starting your trifolium indoors then you might be able to get away with starting them a few weeks earlier.

Last Frost Date

In Washington the average date of last frost happens on April 15. It might get as low as -15°F during the coldest months of winter.

Since the USDA zone info for Washington is not always accurate the actual date of last frost is different every year. Since half of the time in Washington it frosts late in the year after April 15 be ready to protect your trifolium if you have one of those late frosts.

USDA Zone Info for Washington

Here is the info for USDA Zone 5b.

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

Plants to Grow in Washington

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