In the PNW, we have two shorter and cooler growing seasons, spring and fall. While spring crops mature, it is time to think about a second round of cool weather crops for fall cultivating.
There is an abundance of crops and ornamentals to be planted this fall, as the summer heat dissipates. Perennial vegetables and herbs can be transplanted at the end of August, and examples are asparagus and horseradish. Perennial herbs such as sage, thyme, oregano, rosemary, chives, do well when planted in the fall. This is also a great time to plant perennial flowers and bulbs. (Follow bulb planting directions.)
Another option if you want a fall crop is to plant short season, quick maturing crops such as lettuce, arugula, mache, radishes, baby kale, and spinach. In some cases, your crops may overwinter if we have a mild winter. Some crops are not bothered by snow cover and will greet you next spring. (This is my kale crop from two years ago.)
The key to determining if you can get a short season crop is to pay close attention to your seed catalog and seed packet. According to this seed packet for spinach, it can be planted while the soil temperature is 45-75 degrees Fahrenheit and it takes 6-21 days to mature. The crop matures in 45 days. If we count backward from when we get our first frost (around the first week of November), we need to count backward 45+ 14 (an average germination time) days. 45+14 = 59 days and 59 days from November 1st is roughly September 1st. So, September first is the latest you should sow your seeds before the November frost.
Territorial Seed has a fall and winter catalog. I like this company because they test their seeds and crops right here in the Pacific Northwest; also their catalog provides a wealth of gardening information.
Common cool-season vegetables: asparagus, beets, broccoli, Brussels sprouts, chives, cabbage, carrots, cauliflower, Swiss card, kale, leek, lettuce, onion, parsnips, peas, bok-choy, mizuna, mustard greens, chicory, radishes, spinach, fava beans, orach, sorrel, and turnips.
Keep in mind the water shuts off mid-October. We hope you try a fall garden this year!