Southern California falls in USDA plant hardiness zones 8b to 11, where the average range of low temperatures is from 15 to 40 degrees F. Mild winters in these zones make it possible to grow vegetables year-round. Vegetables that are identified as cool-weather crops can be grown throughout the winter in Southern California. Consult a local garden center for specific climate information in your area.
Early spring planting in Southern California is a continuation of cool-season crops such as lettuce, chard, spinach, carrots, radishes and kale. The heritage leek variety known as 'Giant Musselburg' is tender and mild-tasting, and overwinters easily in Southern California. Broccoli raab is a fast-growing vegetable that can be planted in early spring and have at the table in 40 to 60 days. The 'Nautic' variety of Brussels sprouts is also planted in early spring.
When the soil warms to above 60 degrees F in Southern California gardens, it is time to plant tomatoes. Heirloom varieties such as 'Brandywine,' 'German Queen,' 'Armenian' and 'Green Zebra' germinate in three to eight days, and are ready for the table in 70 to 85 days. Pepper varieties such as "Hungarian Yellow Wax Hot' and 'Large Red Cherry' can be planted for a harvest in mid-summer. Pole beans, bush beans, corn and squash can also be planted in summer.
Radishes such as 'French Breakfast' and 'Crimson Giant' can be planted every week from September to March. They are ready to harvest three to six weeks after planting. Onions are also easy to grow, and can be planted in succession from fall to summer. Carrots are a year-round crop in Southern California, and should be planted every one to two months to ensure a constant supply. Carrot seeds are tiny and germinate slowly. Plant winter greens such as chard, kale, collards and spinach, and they will be ready to eat by Thanksgiving.
Seeds germinate more slowly in cool-winter Southern California temperatures but crops may still be planted. Continue to plant greens such as mustard, chard and spinach successively. Beets such as the heirloom varieties 'Chioggia' and 'Bull's Blood' planted in early winter will be on the table in March. Thin beet plants as they grow and use the small plants in salad. Other winter crops are parsnips, carrots, rutabagas and onions.