From Linda Gilkeson:
The first cold weather of the year is forecast to arrive later this week with lows well-below freezing beginning Wednesday night or Thursday. Forecast lows around the south coast range from -4 or -5oC [23-25oF] to what would be extreme cold for this region: -8 to -10oC [14-18oF]—and even colder at higher elevations. Most overwintering vegetables can survive -5oC well enough, but -10oC would severely damage or kill unprotected vegetables out in the garden.
If you still have leaves or straw on hand, fluff an extra thick layer of mulch over the tops of carrots and other root crops, pile it over top of cabbages, radicchio and around leeks and other plants. Throw tarps or plastic sheets over chard, spinach, Chinese cabbage, lettuce and other leafy greens. Hold the covers down with rocks, bricks or boards to keep them in place in high wind (Arctic outflow winds can be very strong!). You can support the covers on short stakes or low wire hoops if desired, but keep them low to avoid catching the wind. You can lay tarps or plastic directly on top of plants if necessary and despite some flattening if snow accumulates, plants usually fare remarkably well. If the cold outbreak dips below -5oC (25oF), winter broccoli, cauliflower and cabbage should be covered to minimize damage. Some varieties are hardy to -9oC (16oF) but not all. At these lows you should also cover rosemary, bay laurel and other less hardy perennials as well as plants growing in unheated greenhouses and tunnels. Garlic shoots poking up now are pretty frost hardy, but it would still be a good idea to cover them with more mulch.
Before freezing weather hits, you might want to harvest as much of your above-ground vegetable crops as you can fit in the fridge. Check that irrigation systems and outdoor taps are drained/insulated as needed. Move potted plants temporarily into a garage or shed or other protected spot for the duration of the cold spell to avoid having the roots freeze (plants will be okay in darkness for a week or so). For more on preparing for a cold blast see my Nov. 22, 2022 and December 19, 2021 messages: Linda Gilkeson || West Coast Gardening || Gardening Tips
Republished with permission from Linda Gilkeson’s Gardening Tips. See Linda’s website to sign up for her newsletter, purchase books, access free presentations and identify pests and diseases which may affect West Coast gardens.