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

By using the USDA zone info for Portland you should be able to figure out when it's possible to plant primroses.

Planting Calendar for Primroses

Frost tolerance for primroses:	Very tolerant of frost.
When to plant:	Up to 7 weeks before last frost.

Primroses do well in cold which tells us that you can plant them much earlier than other frost tender plants.

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

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

Last Frost Date

On average the last frost is on April 15 in Portland. In the coldest months of winter you can expect an average low temperature of -15°F.

Remember that USDA zone info for Portland is just an average and the actual date of last frost will vary from year to year. Half of the time in Portland you get a frost after April 15 so just be sure to be ready to protect your primroses if you have a surprise late frost.

USDA Zone Info for Portland

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 Portland

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