Before planting it is a good idea to find your USDA Zone info to determine your garden schedule. The most important data that the zone info tells us is average last frost and the lowest expected temperature for your area.

The USDA zone info for Portland should be looked at to estimate when it's possible to plant hardy asters.

Planting Calendar for Hardy Asters

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

Since hardy asters are barely cold tolerant you can plant them a bit earlier in the year than other plants that might not handle the cold.

The earliest that you can plant hardy asters 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 hardy asters and expect a good harvest is probably August. Any later than that and your hardy asters may not have a chance to grow to maturity. Starting your hardy asters indoors is a great way to get them started a little bit earlier.

Last Frost Date

The average date of last frost is April 15 in Portland. You can expect an average low temperature of -15°F in the coldest months of winter.

Remember that USDA zone info for Portland is not always accurate and the actual date of last frost will vary from year to year. Half of the time in Portland it frosts late in the year after April 15 so always be ready to protect your hardy asters 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.