Given its multi-faceted and diverse landscape, Arizona has an array of climate conditions that are affected by the Colorado Plateau, Central Highlands, and Basin and Range provinces. Each of these zones is subdivided further to create distinct regions with differing limiting factors for plant growth. Moreover, elevation significantly affects the range of temperatures experienced by each area and the amount of precipitation, as a source of natural moisture, received each year.
Winters in Arizona are thus challenging to describe as a whole. With hardiness zones ranging from 4b – 10b, the state’s chilliest regions may have subfreezing temperatures as low as -25˚F (-32˚C). In contrast, its warmest regions – subtropical deserts located in the southwestern and southcentral areas – have minimum winter temperatures ranging from 30 – 40˚F (-1 to 4˚C). It is crucial to select winter plants based on the microclimate of your particular area as well as its chances of exposure to early and late freezes.
Generally, winter annuals or cold-tolerant perennials that can withstand freezing temperatures are recommended, as the state may experience harsh winter storms. These are typically characterized by strong gusts of freezing winds, icy rain, and sleet. Frost-tolerant flowering species should thrive throughout the state as long as they are afforded ample protection from the elements. Grow these in sheltered spots of the garden, in window boxes, or mixed containers for some cool-season color.
1) Geraniums (Pelargonium spp.)
Geraniums can be grown as flowering annuals in Arizona’s low desert regions, where lows of 47˚F (8˚C) and highs of 68˚F (20˚C) may be observed through winter. Though they do take on perennial growth forms in the wild, they are usually planted into visually eye-catching arrangements during their bloom period. In the subsequent year, gardeners prefer to freshen these arrangements with new tufts of flowering shoots.
The most common geraniums for growth in the US include scented geraniums, ivy geraniums, and zonal geraniums, which are known for the deeper-colored markings on their leaves. These can be planted as early as September, during which they may begin to grace their containers, pots, or plots with vibrant blooms. Given this genus’ many horticultural hybrids, geranium blooms may boast various shades of pink, yellow, orange, red, purple, or white. The blooms may persist throughout warm winters.
Geraniums that are planted towards the end of winter or in early spring may have blooms that last into summer. Hardy to USDA zones 3 – 9, they survive in areas with nighttime winter temperatures briefly dropping to 32˚F (0˚C). Ideally, however, they should be situated in frost-free areas with temperatures ranging from 50 – 60˚F (10 – 16˚C) through the coolest months of the year.
2) Common snapdragon (Antirrhinum majus)
Named for the appearance of their blooms when they are squeezed, snapdragons are some of the most visually arresting flowering plants for winter gardens. Valuable to cool-season pollinators, their inflorescences occur as towering spikes with up to 30 flowers each! Those of the wild forms of this species typically have purple and pink petals, whereas ornamental cultivars exhibit a range of pink, red, orange, yellow, and white tones.
Snapdragons tend to favor Arizona’s dry weather conditions. However, although they may persist as perennials, they are typically cultivated as annuals due to their sensitivity to warm temperatures. They may be planted in the fall, once temperatures have considerably cooled. In some parts of the state, gardeners prefer to plant them outdoors in January and February. Their blooms, which may appear as early as November, may last up to late spring.
Usually placed at the back of container gardens or flower beds, snapdragons can measure as much as 3 feet (91 cm) tall. These plants thrive best under full sun exposure and in well-draining soils with ample moisture. In areas where fall temperatures continue to be markedly warm, consider situating these plants in partial shade, such as below an awning or eave.
3) Winter-blooming pansies (Viola hiemalis)
Often grown as winter annuals, pansies are used to add long-lived color and texture to cool-season flower beds and window boxes. These hardy plants can thrive in the low desert regions of Arizona, where they can be planted from October to February. Also called ice pansies, they require low temperatures to produce their eye-catching and multi-colored blooms. Red, yellow, white, blue, and purple, these blooms can repeatedly appear over the course of 5 – 6 months.
Winter-blooming pansies are best placed in an area where they can receive full sunlight yet remain protected from harsh winds and snowfall. Their 6- to 12-inch (15 – 30 cm) shoots may droop if the substrate is either excessively moist or parched. Day-to-night temperatures ranging between 45 – 65˚F (7 – 18˚C), coupled with low humidity conditions, are best for optimal growth.
4) Petunias (Petunia spp.)
Petunias can be planted throughout winter in the frost-free zones of Arizona. Those that are typically grown in gardens and manicured landscapes are classified as Petunia x atkinsiana hybrids. Some of the most popular tender perennials, oftentimes grown as flowering annuals, flourish in zones with full sunshine, low humidity, and adequate moisture. Though their period of maximum growth usually occurs in late spring, some cultivars can bloom as early as late winter in warm regions.
Particularly beneficial to pollinators, petunias can draw bees and butterflies to your garden during the sunniest and mildest of late winter or early spring days. With fragrant blooms that come in a wide range of colors – purple, pink, yellow, white – and patterned pigments, they are best grown in highly textural bunches and rows. As long as they are provided with some protection from the elements, well-established specimens are usually able to survive through light frosts.
5) Sweet alyssum (Lobularia maritima)
A lovely annual for container gardens, window boxes, and elevated pots, sweet alyssum is set apart by its delicate clusters of honey-scented blooms. Each flower has a maximum diameter of just 0.2 inches (0.5 cm), but they are densely borne on seemingly energetic inflorescences. In regions with frost-free winters, they may be present on well-established shoots throughout the year. Their blooms attract many small insects, which are likely to pollinate nearby plants as well.
Hardy to USDA zones 5 – 9, sweet alyssum naturally spreads towards the edges of its container. It sends out cascades of gravity-defying shoots, which can effectively naturalize raised structures. From a distance, the white blooms (particularly those of the ‘Snow Crystal’ cultivar) may replicate the appearance of a light spray of snow. Those of some horticultural varieties are light purple or pink. Timely trims can encourage the production of more spritely inflorescences.
6) Pot marigold (Calendula officinalis)
Pot marigold makes for a great cool-season plant in the frost-free zones of Arizona. Known for being versatile, forgiving, and suitable for novice gardeners, it can rapidly grow in mild climates. Excessively cool and markedly hot temperatures can damage this species, so it is usually cultivated as an annual. If your area is devoid of winter or early spring freezes, you may sow pot marigold seeds as late as fall. They may sprout quickly enough to produce blooms in winter!
With stems that grow to about 31 inches (79 cm) tall, pot marigold produces hairy, deep-green foliage with either smooth or slightly toothed margins. These make a fine backdrop for the plant’s bright orange blooms, which consist of both ray and disc florets. The blooms attract many pollinators, some of which will lay their eggs on the surrounding foliage. Regularly deadheading spent blooms should enhance the production of new buds.
7) Baja fairy duster (Calliandra californica)
The Baja fairy duster is an evergreen shrub that, in Arizona, may bloom fully in either winter or spring. This slow-growing plant is perfect for desert gardens or Mediterranean-style landscapes, where the substrate is likely to be well-draining and exposed to full sun. Known for the quirky, duster-like appearance of its flowers, which mainly consist of long, red stamens, its vibrance can be maintained throughout the year. The blooms unfailingly attract hummingbirds and bees.
Hardy to USDA zones 9 – 12, the Baja fairy duster is tolerant of a wide range of substrates and becomes increasingly drought-tolerant over time. In winter, its well-established roots can survive being watered just once per month. Cold-tolerant down to about 5 – 22˚F (-15 to -6˚C), this shrub can be used to add long-lived complexity in extensive landscapes experiencing mild climate conditions. Its fern-like leaves, which tend to fold at night, greatly add to its appeal.
8) Firecracker penstemon (Penstemon eatonii)
Perfect for adding striking red speckles to a semi-arid habitat, the firecracker penstemon can reliably bring year-round interest to both small and large gardens in Arizona. Hardy to the moderate temperatures of Phoenix, its small, trumpet-shaped flowers usually appear as early as late winter. These tend to last through spring and may even persist into summer. The blooms are gracefully borne atop towering stalks, creating a spectacular show of seasonal color.
Firecracker penstemon can generally tolerate winter temperatures that drop to around 22˚F (-6˚C). Though it is evergreen, exposure to prolonged or severe frosts can impede its growth and prevent timely flower production. It may be watered in winter, but only if there is minimal rainfall in your area. The rapid drainage of sandy soils should promote root health and lead to successful self-seeding. As the shoots may measure anywhere between 1 – 4 feet (0.3 – 1.2 meters) tall, they can be situated at the forefront or middle row of shrub plantings.
9) Desert globemallow (Sphaeralcea ambigua)
The active growth period of the desert or apricot globemallow is winter or early spring. If it is planted early enough in USDA hardiness zones 6 – 9, it may bloom profusely in late winter. This stunning perennial boasts branching shoots that grow up to 4 feet (1.2 meters) tall in optimal conditions. These bear tri-lobed leaves with a fuzzy and silvery appearance due to a fine layer of hair on both upper and lower surfaces. The attractive foliage complements the cup-shaped blooms, which usually have orange to apricot-toned petals.
As a desert plant, the desert globemallow favors slightly alkaline, sandy, or clay-based substrates. In wild habitats with a Mediterranean-type climate, it tends to grow alongside other drought-tolerant shrubs. For this reason, it is often used to add visual appeal to xeriscapes or desert landscapes requiring restoration. With a peak season lasting from October to May in the lower Sonoran Desert, it is perfectly compatible with Phoenix’s winter conditions.
10) Cape honeysuckle (Tecoma capensis)
In warm regions, the cape honeysuckle may stun viewers with its year-round display of red-orange flowers. These are beautifully arranged in clusters arising from the tips of fine, woody branches. Versatile, the stems can be encouraged to form a tall shrub (4 – 8 feet or 1.2 – 2.4 meters) or a brambling vine – one which boasts a coverage reaching heights of 25 – 30 feet (7.6 – 9 meters)! Due to its sheer capacity for growth, this species may require frequent pruning each year.
Hardy to USDA zones 9 – 11, the cape honeysuckle tolerates winter temperatures down to around 41˚F (5˚C). In regions with cooler winter temperatures, specimens that are situated in pots may need to be overwintered indoors. In many parts of Arizona, however, this species can prove to be a lasting type of groundcover or hedge that tolerates outdoor conditions through all the seasons. If unexpected freezes do occasionally occur in your area, pruning frost-damaged stems should benefit the plant.
