One of the best tools that you have as gardeners to help us estimate your gardening schedule is the USDA zone info. The zone info helps tell us things like average date of last frost and lowest expected temperature for your area.

By using the USDA zone info for Portland you should be able to figure out when 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 tells us that you can start planting them slightly earlier than other plants that might not handle the cold.

The earliest that you can plant trifolium in Portland 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

In Portland the average date of last frost happens on April 15. You should expect an average low temperature of 0°F in the coldest months of winter.

Always keep in mind that USDA zone info for Portland is just an average and the actual date of last frost changes from year to year. Since half of the time in Portland there is a last frost after April 15 be ready to cover your trifolium in the event of a late frost.

USDA Zone Info for Portland

Here is the info for USDA Zone 7a.

Average Date of Last Frost (spring)	April 15
Average Date of First Frost (fall)	October 15
Lowest Expected Low	0°F
Highest Expected Low	5°F

This means that on a really cold year, the coldest it will get is 0°F. On most years you should be prepared to experience lows near 5°F.

Plants to Grow in Portland

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