Protecting Your Plants From Frost
As we wind down winter, let’s take a moment to talk about frost. Before you start running to the nursery to plant those adorable little vegetable starts, let’s make sure we check your last frost date. Here in Sonoma County my lose rule is to wait until after Easter to plant the vegetable starts out in the garden.
Last Frost Date Checker
https://www.almanac.com/gardening/frostdates
Understanding the impact of freezing temperatures on your garden is crucial for maintaining plant health and ensuring a vibrant landscape come spring. In Sonoma County, where temperatures can occasionally dip below freezing, it's essential to recognize how cold affects soil and plants, identify frost-sensitive species, and implement effective protection strategies. I will be approaching this from the perspective of our region, however I’m happy to answer questions as I’ve also gardened in Northern regions that get harder freezes and even snow.
Some winter crops like kale become sweeter after frost.
The Effect of Below-Freezing Temperatures on Soil and Plants
What actually happens when the weather drops below zero. The water in both your plants and the soil expands as it freezes. This expansion can burst plant cells, burst pots and disrupt the soil structure. Before we can talk about the ways to protect your garden we need to understand the science of freezing.
When temperatures drop below freezing, several changes occur in the soil and plants:
Soil
How does frost help your soil?
Improved Soil Aeration: Freeze–thaw cycles break apart compacted soil layers, creating pores and improving soil aeration. This enhances root penetration and allows for better gas exchange.Breakdown of Organic Matter: Frost can fragment plant residues and organic materials on the soil surface, making them more accessible to microorganisms for decomposition. This process enriches the soil with nutrients.
Natural Soil Tillage: The expansion and contraction of soil during frost work similarly to tillage, loosening the soil without mechanical intervention, especially beneficial for heavier clay soils.
Pest Control: Freezing temperatures can reduce populations of soil-borne pests and pathogens, providing a natural form of pest control.
Seed Stratification: For certain plants, frost is essential for breaking seed dormancy. The cold period triggers germination in some species, particularly those native to temperate climates.
(Sources: Copernicus, Springer, Wikipedia)
Frozen leaves and grass.
Delicate winter crops like chard will wilt after a frost because their cell walls burst.
Plant Cells
In plants, freezing temperatures can lead to the formation of ice crystals within cells, causing cell walls to rupture. This damage manifests as wilted or discolored foliage and can be fatal if severe. (The Spruce)
Root Systems
Roots are generally less cold-hardy than above-ground parts. Frozen soil can damage shallow roots, impairing the plant's ability to absorb water and nutrients, which may result in stunted growth or death. (UMass Extension)
Plants that are frost hardy benefit from frost.
Frost-Prone Plants in Sonoma County
While Sonoma County's mild climate supports diverse plant life, certain species are particularly vulnerable to frost damage:
Tender Annuals: Plants like marigolds (Tagetes spp.), impatiens (Impatiens walleriana), and petunias (Petunia spp.) are sensitive to frost and can suffer significant damage or death when exposed to freezing temperatures. (Garden Skill)
Subtropical Species: Plants such as citrus trees (Citrus spp.) and bougainvillea (Bougainvillea spp.) thrive in warmer climates and are susceptible to frost injury, which can cause leaf drop and dieback.
Succulents and Cacti: While some succulents are frost-tolerant, many, including jade plants (Crassula ovata) and certain agaves (Agave spp.), can suffer tissue damage when temperatures fall below freezing.
Identifying and monitoring these vulnerable plants is essential for implementing timely protective measures.
Creating tents for citrus trees allows air flow but protects from the hardest frosts. On this project we also added christmas lights to generate some heat.
Protecting Plants, Soil, and Pottery from Freezing Temperatures
To safeguard your garden during cold spells, consider the following strategies:
Mulching: Apply a 2- to 4-inch layer of organic mulch, such as straw or wood chips, around the base of plants to insulate the soil and roots, moderating temperature fluctuations. (The Spruce)
Covering Plants: Use frost cloths, blankets, or burlap to cover sensitive plants during frosty nights. Ensure covers extend to the ground to trap warmth and remove them during the day to prevent overheating. (The Spruce)
Watering: Moist soil retains heat better than dry soil. Watering the ground around plants before a freeze can help maintain a warmer root environment. (The Spruce)
Planting delicate plants in pots allows you to move them in the winter to more protected areas.
Relocating Potted Plants: Move container plants to sheltered areas, such as garages or indoors, to protect them from freezing temperatures. If moving isn't feasible, cluster pots together against a south-facing wall and wrap them with insulating materials. (The Spruce)
Using Wind Machines: For larger gardens or orchards, wind machines can circulate warmer air, reducing frost formation on plants. (Sonoma Ag Preservation)
Implementing these practices can significantly reduce frost damage, ensuring your plants remain healthy throughout the winter.
Conclusion
Understanding the effects of freezing temperatures on soil and plants, recognizing frost-sensitive species in Sonoma County, and employing protective measures are vital steps in maintaining a resilient and thriving garden. By proactively addressing the challenges of cold weather, you can safeguard your plants and enjoy a flourishing landscape year-round.
Sources
Flourishing Plants. "Can Soil Freeze: Causes, Depth, and How it Affects Plants." https://flourishingplants.com/can-soil-freeze/
The Spruce. "What You Should Do Right Now to Keep Your Plants Safe From Frost This Winter." https://www.thespruce.com/how-to-protect-plants-from-frost-this-winter-8750453
Gardenia. "Frost Damage: Identify, Prevent and Treat it." https://www.gardenia.net/guide/frost-damage
The Spruce. "How to Overwinter Your Plants to Keep Them From Dying in the Winter Cold." https://www.thespruce.com/how-to-overwinter-plants-8749052
Sonoma County Winegrowers. "Frost Protection and Water Conservation." https://sonomawinegrape.org/grower-resources/frost-protection-and-water-conservation/
University of California Agriculture and Natural Resources. "Recommended Plants for Sonoma County." https://ucanr.edu/sites/scmg/files/303865.pdf
Purdue University. "Effects of Cold Weather on Horticultural Plants in Indiana." https://www.purdue.edu/hla/sites/yardandgarden/extpub/effects-of-cold-weather-on-horticultural-plants-in-indiana/
Farmers' Almanac. "Protect Outdoor Plants From Frost." [https://www.farmersalmanac.com/frost-temperature-outdoor