- Author: By Sherida Phibbs, UC Master Gardener
In this article, we'll dive into the specifics of frost and freeze protection—vital information for this time of year. I'll also share details about growing citrus in containers and some of the plants chosen for my landscape. If you missed the earlier articles, Part One covered the planning process for my landscape, and Part Two focused on irrigation setup and an initial look at plant selection.
Let's explore how to prepare your garden for the cold and ensure it continues to thrive through the winter.
Preparing Your Garden for Frost And Freeze
In San Joaquin County, where winters are mild but unpredictable cold snaps do occur, gardeners face unique challenges in protecting plants from frost, light freezes, and the occasional hard freeze. With the right techniques and planning, it's possible to safeguard gardens against these chilly conditions and keep plants healthy through the colder months.
Understanding the Threat: Frost, Light Freeze, and Hard Freeze
Cold temperatures can vary in intensity and have different effects on plants:
- Frost – Frost forms when temperatures hover around 32°F or slightly above. As surfaces like leaves and grass cool, water vapor condenses and freezes on them. Frost can damage tender leaves, buds, and flowers, especially on plants like tomatoes and basil.
- Light Freeze – When temperatures fall between 29°F and 32°F, a light freeze occurs. This can damage sensitive plants and buds on fruit trees, especially early bloomers like apricots and citrus. Tropical plants and succulents may suffer leaf or stem damage.
- Hard Freeze – A hard freeze, with temperatures 28°F or below, can cause significant damage. These conditions, often lasting several hours, are especially challenging for less cold-hardy perennials and the roots of tender plants. Hardy plants may survive but can still sustain damage if exposed too long.
Frost and Freeze Concerns in San Joaquin County
Though San Joaquin County has a Mediterranean climate, the cooler months from November through February occasionally bring frost or freeze conditions. The county's topography and microclimates can make certain areas more prone to frost accumulation.
Many plants benefit from covering with frost cloths or blankets, watering prior to a freeze, and mulching around their bases to insulate the roots. Listed below are categories of plants that may need protection during cold weather (not an exhaustive list):
- Fruit trees and fruit-bearing trees including citrus (especially lemons, limes, and oranges), avocado, fig, loquat, and olive.
- Tropical and subtropical plants including banana, bird of paradise, bougainvillea, hibiscus, jade plant, and plumeria.
- Perennials and flowering ornamentals including the passion vine, begonias, fuchsias, lantana, and geraniums.
- Succulents and cacti including aloe vera, echeveria, kalanchoe, and jade plant.
- Young or newly transplanted trees and shrubs (e.g., oak, Japanese maple, and other semi-hardy varieties) are vulnerable to frost and may need extra insulation during the first few years until they are well established.
Using Water to Protect Plants from Freeze
Watering plants (except for succulents) before a freeze is an effective strategy to help protect them from damage:
Moist soil holds heat better than dry soil, absorbing warmth from the sun during the day and releasing it slowly at night. This creates a buffer against the chill, helping to stabilize temperatures around plants.
Hydrated plants are more resilient to cold, as water in their cells provides a layer of insulation. Drought-stressed plants are more vulnerable, as they lack moisture to protect their cells.
Deep watering in the morning or early afternoon is ideal, so the soil can absorb heat throughout the day. Avoid creating overly saturated conditions, as this can lead to root issues. Don't wet the leaves, especially if using overhead watering, as ice formation on leaves can increase damage.
Covering Plants: Choosing the Right Materials
Covering plants before frost or freeze conditions can help protect them, but not all materials are suitable. Plastic coverings, for example, are generally discouraged. While they may seem convenient, plastic has some drawbacks. Plastic transfers cold quickly, so if it touches plant leaves, it can cause more harm than good. Plastic can create condensation on the inside, which may lead to frost formation directly on the plants.
The best materials for covering plants are frost cloths or row covers. They are lightweight and breathable and allow air circulation while insulating plants from the cold. Household blankets, old sheets, or towels offer effective insulation and help prevent direct contact with frost. These can be propped up with stakes or support to avoid crushing plants. Burlap is a good choice as its breathable material works well for wrapping shrubs or small trees, allowing airflow and providing a warm buffer against the cold.
Save those boxes as small plants can be covered with overturned cardboard boxes, secured around the edges to prevent them from blowing away. Arrange the material in a tent-like structure over plants, preventing it from touching leaves or branches directly. Make sure the edges of the cover reach the ground and are secured with bricks, stones, or soil to trap warmth rising from the soil. Remove the cover in the morning, once temperatures rise above freezing. Leaving covers on during warmer days can cause plants to overheat.
Final Tips for Garden Protection
A thick layer of organic mulch (like straw or shredded leaves) around the base of plants provides insulation, keeping roots warm and helping to regulate soil temperatures.
Be proactive by covering plants and watering them in the afternoon before a freeze is expected. This gives the soil time to retain warmth from the sun during the day.
Be mindful of your garden's unique microclimate. Areas near walls or under trees are often more protected from frost, while open spaces may need extra attention.
By understanding the effects of frost and freeze, preparing plants with water and covers, and using the right techniques for San Joaquin County's climate, you can protect your garden through winter. With these steps, your plants will be ready to thrive when spring returns.
Featured Plants in My Garden
Lavandula stoechas: Adding Beauty and Fragrance
I've selected two stunning cultivars of Lavandula stoechas, commonly known as Spanish lavender— ‘Winter Bee' and ‘Primavera'—to border a small island and pathway in my garden. Both are well suited for Mediterranean-climate gardens, offering vibrant color and a delightful fragrance while being easy to care for. These lavenders also attract bees, butterflies, and other pollinators, making them a valuable addition to any pollinator-friendly landscape.
In their natural Mediterranean habitat, Lavandula stoechas thrives in rocky, well-drained soils and is perfectly adapted to hot, dry summers and mild, wet winters. Their drought tolerance and love of full sun make them an ideal choice for gardens in the Central Valley.
The genus Lavandula comes from the Latin word "lavare," meaning "to wash." Historically, lavender was prized for its pleasant scent and purported antiseptic properties. The ancient Romans famously used lavender in their baths, giving rise to its name.
The species name "stoechas" is thought to come from the Stoechades Islands (modern Îles d'Hyères) off the southern coast of France, where the plant was found in abundance. These islands lent their name to the species, tying it to its Mediterranean roots.
Lavandula stoechas ‘Winter Bee' is renowned for its ability to bloom during cooler weather, often beginning in early spring and continuing through late summer, and sometimes extending into autumn if conditions remain mild. Its deep purple flowers, topped with prominent bracts (or “rabbit ears”), are characteristic of the L. stoechas species and draw bees, butterflies, and other pollinators to the garden.
This compact, dense shrub reaches about 18-24 inches in height and spreads similarly wide. Its silvery-green, aromatic leaves are evergreen in mild climates, providing year-round interest. ‘Winter Bee' tolerates cooler conditions better than many other lavenders, making it a versatile choice for a variety of landscapes.
Ideal for sunny locations such as borders, containers, or mass plantings, the fragrant foliage and flowers are perfect for sensory gardens or sunny, drought-tolerant landscapes. Provide full sun and well-drained soil. While the plant is drought-tolerant once established, it is essential to ensure good drainage to prevent root rot.
To keep ‘Winter Bee' looking its best, prune it lightly after its first flowering in spring and again in late summer to remove spent flowers and maintain a compact shape. Avoid cutting into old, woody stems, as this may limit new growth. Regular pruning encourages more blooms and a bushier appearance.
Lavandula stoechas ‘Primavera' stands out for its extended bloom season, which typically starts in early spring and continues through the summer. In regions with mild winters, it may even flower during the colder months. The violet-purple flowers, with their distinctive upright bracts, attract pollinators just like other L. stoechas varieties.
A bushy, compact shrub, ‘Primavera' grows to about 18-24 inches in height and up to 2 feet wide, making it a great choice for borders, rock gardens, or containers. Its grey-green, aromatic leaves are evergreen in warmer climates, adding texture and interest year-round.
Thriving in USDA zones 7-9, ‘Primavera' is particularly known for its early and long-lasting blooms, making it ideal for gardeners seeking continuous color. As with other lavenders, Primavera' prefers full sun and well-drained soil. While it is drought-tolerant, ensuring proper drainage is essential to avoid root diseases.
‘Primavera' benefits from a light trim after each flush of blooms to encourage continuous flowering throughout the growing season. Prune in early spring to remove any dead or damaged stems and again after flowering to shape the plant and promote healthy new growth. As with ‘Winter Bee,' avoid cutting into the older, woody parts of the plant to prevent damage.
Both ‘Winter Bee' and ‘Primavera' offer a combination of beauty, fragrance, and low maintenance, making them perfect for gardeners looking to enhance their Mediterranean-style landscape or add pollinator-friendly plants to their garden. Pruning these lavenders regularly not only keeps them looking neat but also encourages a fuller, more vigorous growth and an abundance of blooms.
Loropetalum Chinense ‘Kurenai': Captivating Color and Easy Care
The Chinese fringe flower ‘Kurenai,' also known as 'Jazz Hands,' is a showstopping shrub, celebrated for its hot-pink spring blooms and striking purple-black foliage. Unlike its larger relatives, this compact variety reaches a manageable 3–5 feet in height and width, making it a perfect fit for smaller gardens or as a colorful landscape accent. While it primarily dazzles in spring, it may offer a delightful encore of blooms in summer. As fall arrives, its foliage transforms into a rich red, adding year-round visual interest.
Loropetalum chinense 'Kurenai' is a cultivar of the Chinese fringe flower, native to China, Japan, and the Himalayas. This variety, introduced more recently, is renowned for its striking red to purple leaves and vibrant pink, fringe-like flowers. The name "kurenai," derived from a Japanese word meaning "crimson" or "deep red," reflects the cultivar's vivid foliage. Though Loropetalum chinense has been a beloved garden plant for centuries, 'Kurenai' has gained particular popularity for its compact size and vibrant color, making it a standout in ornamental landscaping. Developed by horticulturalists, possibly in Japan or the U.S., in the late 20th century, this cultivar was selectively bred for its unique combination of foliage and flowers—ideal for those seeking a plant that offers both beauty and ease of care.
I chose two of these stunning plants for my own landscape, drawn by their adaptability and ornamental appeal. Loropetalum chinense 'Kurenai' thrives in full sun to partial shade and prefers rich, well-draining loamy soil with a slightly acidic to neutral pH. Keep the soil consistently moist while the plant is young, but once established, it becomes impressively drought-tolerant, making it a fantastic option for a low-maintenance garden.
For best results, fertilize in spring and early summer with an all-purpose, slow-release fertilizer. This hardy shrub can withstand temperatures as low as 0°F but will benefit from protection against harsh winds. Light pruning after flowering helps maintain its compact, mounded shape and encourages lush new growth.
Growing Dwarf Citrus Trees in Containers
Three potted dwarf citrus trees welcome visitors as they approach the front porch, adding a delightful, fragrant sensory experience during their blooming season. I selected the warmest location for these trees—lemon, blood orange, and mandarin orange—placing them in large pots along the side of the house by a cement walkway. The reflective heat from the sidewalk and house provides additional warmth during colder months, while the overhang of the roof and proximity to the house offer some frost protection. However, when a hard freeze is predicted, I plan to cover the trees with burlap, as citrus is not hardy below 32°F.
Citrus trees require regular fertilization in the spring, summer, and fall. They prefer soil that is consistently moist but not waterlogged. When growing citrus in containers, it's essential to use pots with excellent drainage and fill them with high-quality citrus or regular potting soil. Repotting every two to three years helps refresh the soil and prevents the trees from becoming root bound, ensuring they remain healthy and productive. During the growing season, which typically spans spring through summer, citrus trees benefit from a fertilizer rich in nitrogen, applied every 6–8 weeks. Feeding can be reduced in fall and winter when growth slows.
Pruning is best done lightly in late winter or early spring to shape the trees, remove dead or crossing branches, and improve airflow. Heavy pruning should be avoided, as it can reduce fruit production. Citrus trees thrive in full sun, requiring at least 6–8 hours of sunlight daily for healthy growth and abundant fruiting. They prefer well-draining soil with a slightly acidic pH of 6.0–7.0. While mature trees are moderately drought-tolerant, regular deep watering is important, especially during the establishment phase or hot, dry periods. Deep watering during fruiting also ensures optimal growth and a robust harvest.
Caring for citrus involves staying vigilant for common pests such as aphids, scale, and spider mites, which can be managed with horticultural oil or insecticidal soap. Protecting the trees from frost during cold snaps is crucial to maintaining their health and productivity. With proper care and attention, dwarf citrus trees can thrive in containers and bring beauty, fragrance, and fruit to your home garden.
Citrus limon ‘Eureka' traces its origins to California in the mid-19th century. It was first propagated in 1858 by Thomas Garey, a nurseryman in Los Angeles, using seeds imported from Sicily, Italy. This variety quickly rose to prominence in the United States for its vigorous growth, high productivity, and ability to produce fruit nearly year-round. Its Italian heritage, combined with its refinement in California, has made the Eureka lemon a hallmark of premium quality, prized for its juicy, tangy flavor and thin, fragrant rind.
Unlike many citrus varieties, the Eureka lemon is not particularly cold-hardy and thrives in warm climates. The dwarf version of this iconic lemon is especially popular for home gardens and patios, as its compact size makes it ideal for growing in containers. When planted in the ground, the dwarf tree typically reaches 8–10 feet in height but remains smaller when confined to a pot, making it perfect for spaces with limited room.
Eureka lemons are best harvested when their skin turns a vibrant yellow and the fruit feels slightly firm to the touch. It is important to note that lemons do not continue to ripen once picked, so harvesting them at their peak ensures the best flavor. In addition to its reliable fruit production, the dwarf Eureka Lemon tree contributes a lush, evergreen presence to gardens, offering beauty year-round.
With proper care, this versatile tree not only provides an abundant supply of fresh, flavorful lemons but also serves as a decorative element in outdoor spaces. The Eureka lemon dwarf tree is a practical and charming choice, bringing both utility and elegance to any home garden.
Citrus reticulata ‘Owari' is a hardy and flavorful mandarin orange with a rich history rooted in Japan, where it has been cultivated for centuries. The term "Satsuma" originates from the historic Satsuma Province, now part of Kagoshima Prefecture, a region renowned for growing and exporting these mandarins. While its cultivation flourished in Japan, the variety is believed to have originated in China before being introduced and refined in Japan.
Owari is one of the oldest and most esteemed Satsuma cultivars, celebrated for its sweet flavor, almost-seedless fruit, and exceptional cold tolerance. Its introduction to the Western world occurred in the 19th century, and it gained popularity in the United States, particularly in regions with mild winters, such as the Gulf Coast and California. Today, the Owari Satsuma mandarin is beloved globally for its adaptability and high-quality fruit.
Its fruit ripens in late fall to early winter, generally between October and December, offering a bright orange color, delicate fragrance, and sweet, tangy flavor. The mandarins are easy to peel and virtually seedless, making them a favorite for fresh eating and culinary uses.
Knowing when to harvest Owari Satsuma mandarins is key to enjoying their full flavor. The fruit is ready to pick when it develops a deep orange hue and feels slightly soft to the touch. Unlike some citrus varieties, mandarins can continue to ripen slightly on the tree, but their flavor and sweetness are at their peak once the skin has fully colored. Its fruit is versatile, whether enjoyed fresh, used in recipes, or preserved. For example, I enjoy adding mandarin oranges to salads. After supreming (eliminating the pith and tough membranes) the fruit for easy-to-eat segments, I often preserve them by canning. If you're interested in learning how to supreme citrus, check out the article I wrote for the UC Master Food Preservers.
Citrus sinensis ‘Moro' is a stunning and flavorful blood orange variety prized for its distinctive crimson flesh and rich, tangy-sweet flavor. Believed to have originated in Sicily, Italy, during the early 19th century, this variety of blood orange is thought to be a natural mutation of the sweet orange (Citrus sinensis). Its vibrant color and unique flavor profile, often described as having hints of raspberry or berry-like notes, make it a favorite among citrus lovers and chefs alike.
The fruit of the Moro blood orange is typically ready for harvest in late winter to early spring, usually from January through March, depending on the climate and growing conditions. The fruit is at its peak ripeness when the skin develops a deep reddish-orange blush, and the flesh inside has achieved its characteristic crimson color. To ensure the best flavor, the fruit should feel firm but slightly yielding to the touch and detach easily from the tree. Unlike some citrus fruits, blood oranges do not ripen further after being picked, so harvesting at the right time is crucial.
The Growing Season: A Year of Landscape Transformation
I'm excited to share the final article in the Transforming Your Landscape series in the spring edition of our newsletter! In it, I'll highlight more of my favorite plant selections, the progress of my landscape as it continues to acclimate and thrive, and even more helpful tips to inspire your own transformations. I can't wait for you to join me on this journey—stay tuned!
References:
Transforming Your Landscape Part One
Transforming Your Landscape Part Two
Approximate First and Last Frost Dates in California
Frost and Protection for Sensitive Plants
Lavandula stoechas ‘Winter Bee'
Lavandula stoechas ‘Primavera'
Chinese Fringe Flower ‘Jazz Hands'
Growing Citrus in Patio Containers
