December in California is a crucial period for planting, capitalizing on the mild winter conditions across much of the state. This month offers a significant advantage for establishing a cool-season garden, allowing plants to develop robust root systems before the heat of late spring and summer arrives. Strategic planting in December ensures a bountiful harvest and vibrant floral displays early in the new year.
Understanding California’s Diverse Winter Planting Regions
California’s unique geography creates distinct microclimates, making a single, statewide planting guide impractical for December. Winter gardening advice is divided into three primary zones based on temperature and frost likelihood. The most populated areas, encompassing the Mild Coastal and Inland Valleys, experience cool temperatures with little to no hard frost, making them ideal for continuous cool-season growth.
The second category is the Low Desert, which includes areas like the Coachella and Imperial Valleys, characterized by very mild, warmer winters that allow for the cultivation of specific, cold-sensitive crops.
Finally, the High Elevation and Mountain zones experience hard freezes and snow, requiring plants to enter a complete dormancy period. Gardeners in these frost-prone areas must focus on protective measures and planting items that require a chilling period.
Cool-Season Vegetables for Coastal and Inland Valleys
For the Mediterranean climates of the coastal regions and the Central Valley, December is the peak of the cool-season vegetable planting window. Direct sowing and transplanting cool-tolerant crops now ensures they mature before the spring temperature spike causes them to bolt. Many popular brassicas, which thrive in temperatures between 55°F and 75°F, can be planted from transplants this month for a late-winter or early-spring harvest.
Transplants for crops like broccoli, cabbage, and cauliflower should be set out now, benefiting from the entire winter growing period due to their long maturity times. For root crops, December is an excellent time to direct-sow seeds for carrots, beets, radishes, and turnips. The cooler soil temperatures help sweeten the roots and prevent bolting that can occur with warmer spring planting.
Leafy greens, including spinach, Swiss chard, and various lettuce varieties, can be continuously sown from seed throughout December for a steady supply of fresh leaves. These crops are highly tolerant of light frost, which actually improves their flavor profile, a process known as cold-sweetening.
Flowers, Bulbs, and Ornamentals for Winter Color
December is the optimal time for planting dormant, bare-root material, which includes deciduous fruit trees, grapevines, and roses. Planting these items while they are dormant reduces transplant shock and allows the root system to establish itself in the cool, moist soil before spring growth begins.
Spring-blooming bulbs that require a chilling period, such as tulips and daffodils, should be planted now if they have been pre-chilled in a refrigerator for at least six weeks. This cold treatment is necessary to break dormancy and ensure proper flower development, particularly in California’s mild winter zones where the ground does not freeze consistently.
For immediate color, cool-season annuals like pansies, violas, and cyclamen can be planted as transplants in beds and containers. These plants will provide vibrant blooms throughout the winter and into early spring, thriving in the lower light and cooler temperatures of the season.
Planting Strategies for Desert and High Elevation Zones
Gardening in California’s climatic extremes requires a highly specialized approach in December, focusing on protection in the mountains and leveraging the mild temperatures in the desert. In the Low Desert areas, the winter is actually the primary growing season, allowing for the planting of crops that would typically be spring plantings elsewhere. Specific varieties of peas, which appreciate warm winter soil, can be planted now, often benefiting from the use of floating row covers to moderate temperatures during occasional cold snaps.
For mountain and high-elevation zones, where hard freezes are a certainty, the focus shifts away from active planting to preparation and strategic overwintering. December is the last opportunity to plant hardneck garlic, which requires an extended period of cold stratification below 40°F to form large, segmented bulbs.
Garden beds not in use should be heavily mulched with straw or leaves to protect the soil structure and beneficial organisms from deep freezing. This protective layer is also important for insulating the roots of perennials and preparing the ground for an earlier spring thaw.