One of the first steps you take when you are getting a good idea 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 Portland you can determine when you can plant thunbergia by referring to the USDA zone info.

Planting Calendar for Thunbergia

Frost tolerance for thunbergia:	Not tolerant of frost.
When to plant:	After the last frost has passed.

Thunbergia are not cold tolerant which means that you really should wait until it warms up after all chance of frost has passed before you can plant them.

The earliest that you can plant thunbergia in Portland is April. However, you really should wait until May if you don't want to take any chances.

The last month that you can plant thunbergia and expect a good harvest is probably August. You probably don't want to wait any later than that or else your thunbergia may not have a chance to grow to maturity. Starting your thunbergia indoors is a great way to get them started a little bit earlier.

Last Frost Date

In Portland the average date of last frost happens on March 15. In the coldest months of winter you should expect an average low temperature of 15°F.

It's important to remember that the actual date of last frost is not always accurate because it is based on the USDA zone info for Portland and it can change quite a bit from year to year. Since half of the time in Portland you get surprised by a frost after March 15 be ready to cover your thunbergia in the event of a surprise late frost.

USDA Zone Info for Portland

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 Portland

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