One of the first steps you take when you are figuring out 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.

A way of estimating when it's a good idea to plant purple rock cress is to look at the USDA zone info for Seattle.

Planting Calendar for Purple Rock Cress

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

You can plant purple rock cress quite a bit earlier in the year because they do well in cold.

The earliest that you can plant purple rock cress in Seattle 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 purple rock cress and expect a good harvest is probably September. Any later than that and your purple rock cress may not have a chance to really do well. You can get started a little bit earlier by starting your purple rock cress indoors.

Last Frost Date

On average all chance of frost has passed is on March 15 in Seattle. In the coldest months of winter you can expect an average low temperature of 15°F.

It's important to remember that the actual date of last frost is an average because it is based on the USDA zone info for Seattle and it is different every year. Half of the time in Seattle last frost occurs after March 15 so just be sure to be ready to protect your purple rock cress in the event of a surprise late frost.

USDA Zone Info for Seattle

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 Seattle

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