December offers a distinctive opportunity for gardening in Arizona, providing a vibrant second growing season while much of the country is dormant. The mild winter weather in the state’s lower elevations allows a variety of cool-season vegetables, herbs, and flowers to be successfully planted and harvested throughout the winter months. This period enables gardeners to cultivate crops that would perish under the summer’s intense heat. Success depends on understanding the stark climatic differences across Arizona’s geography.
Understanding Arizona’s December Climate Zones
Arizona’s vast topography creates two distinct gardening climates in December. The Low Desert region, including Phoenix, Tucson, and Yuma, is characterized by USDA Hardiness Zones 9b to 10a. Daytime temperatures typically range from 60°F to 70°F, supporting continuous cool-season growth, though gardeners must be prepared for light, sporadic frost.
Conversely, the High Desert and mountainous regions, such as Flagstaff, Prescott, and Payson, fall into colder zones (5b to 7a). These higher elevations experience hard freezes and snow, halting traditional outdoor gardening and requiring a focus on protection or indoor starting. The difference in minimum winter temperatures dictates which plants will survive and thrive in each location.
Low Desert Planting: Cold-Tolerant Vegetables and Herbs
December is an ideal time for planting cool-season food crops in the Low Desert, using either direct-seeding or transplants.
Leafy Greens and Brassicas
Leafy greens are tolerant of the mild cold and should be planted now for a steady harvest. These can be continuously harvested using the “cut-and-come-again” method.
- Arugula
- Spinach
- Leaf lettuce
- Swiss chard
Brassicas, including broccoli, cauliflower, cabbage, and kale, should be planted, preferably as transplants, to ensure a harvest before the spring heat arrives. Peas can also be sown now; they benefit from soaking overnight before planting and should be trellised to maximize space.
Root Vegetables and Herbs
Root vegetables require direct seeding to ensure proper taproot development. Carrots, beets, radishes, and turnips should be sown about a half-inch deep and kept consistently moist until germination for an early spring harvest. Radishes are fast-growing and can be succession-sown throughout the month for a quick yield. Cool-season herbs, including cilantro, dill, parsley, and chives, also thrive in December and can be planted from seed or transplant.
Low Desert Planting: Winter Flowers and Ornamentals
For aesthetic appeal, December is the time to introduce vibrant cool-season annuals that provide color throughout the winter and early spring.
Annuals and Bulbs
Pansies and violas offer cheerful blooms and thrive in full to partial sun. Snapdragons add vertical interest and should be planted from young seedlings in full sun. Other colorful options include:
- Calendula, which displays warm orange and yellow flowers.
- Sweet alyssum, which creates a low-growing, fragrant border.
Planting bulbs for spring flowers, such as ranunculus and anemone, should also be done this month. These bulbs require the winter soil chill to set their blooms for a spring display.
Trees and Shrubs
December is also the time to plant hardy deciduous and citrus trees, allowing root systems to establish in the cooler soil before summer heat. Planting cold-hardy shrubs and perennials now gives them a head start. For example, the Baja Fairy Duster is a low-maintenance shrub that provides unique red blooms in the winter.
High Desert Considerations and Winter Plant Care
High Desert Focus
In the High Desert regions, December planting is limited by frozen ground and hard freezes. Gardeners should focus on protecting existing plants and preparing for spring. The primary exception for outdoor planting is hardier garlic, which should be planted as individual cloves beneath a thick layer of mulch to survive the winter and begin growth in spring.
General Winter Care
Winter plant care for all Arizona gardeners centers on frost protection and adjusting watering schedules. Even in the Low Desert, frost can damage sensitive new plantings. Materials like frost cloth or row covers should be used when temperatures are forecast to drop below 32°F. New citrus trees require protection from freezing temperatures.
Watering frequency must be reduced due to cooler temperatures and shorter daylight hours, which slow plant metabolism. Garden beds should only be watered when the soil is dry a few inches below the surface, usually about once a week, ensuring deep saturation to encourage healthy root development.