Garlic is a notably cold-tolerant plant that can generally survive frost. This hardy bulb, typically cultivated as an annual crop, possesses natural adaptations allowing it to withstand freezing temperatures during its underground development. In fact, a period of sustained cold is necessary for the plant to properly develop the segmented bulb that is harvested.
Garlic’s Requirement for Cold
Garlic requires cold exposure to trigger the complex process of bulb division. This chilling period, known as vernalization, is necessary for the plant to transition from vegetative growth into forming multiple cloves. Without this exposure, the plant will likely produce a single, undivided bulb, often called a “round.”
The ideal chilling period for most varieties is between 30 and 120 days, with temperatures remaining below 40°F (4°C). Fall planting allows the clove to establish roots before the ground freezes, enabling the bulb to enter a state of deep rest, shielded by the soil. While the green tops of the plant may suffer damage during severe frost, the vital bulb remains protected underground, preparing for spring growth.
Differences in Garlic Type Hardiness
Garlic varieties are categorized into two main types with distinct levels of cold tolerance. Hardneck varieties are significantly more cold-hardy and are the preferred choice for regions with severe winters. These types require an obligate vernalization period to form their characteristic flowering stalk, or scape, and to properly segment the bulb.
Softneck varieties are much less cold-tolerant and thrive best in environments with milder winters. They require less chilling to produce a segmented bulb, making them suitable for warmer regions where the ground may not freeze deeply. Although softnecks can be grown in colder areas, they are less durable against extreme cold than hardneck varieties.
Safeguarding Garlic from Freezing Temperatures
While garlic is naturally tough, growers can employ specific techniques to protect the bulbs from temperatures exceeding the plant’s natural tolerance. The depth of planting provides the first line of defense against freezing soil temperatures. Planting cloves approximately 2 to 4 inches deep helps insulate the developing bulb and anchors it firmly in the soil.
Applying a thick layer of organic mulch, such as straw or shredded leaves, is the most effective action a grower can take before the ground freezes. A protective layer of 4 to 8 inches insulates the soil and prevents repeated freezing and thawing cycles. This insulation prevents a phenomenon called frost heaving, where the expansion and contraction of freezing soil pushes shallow bulbs out of the ground, exposing them to lethal cold and desiccation.
In early spring, once the worst of the cold has passed, it is beneficial to partially pull back the thick mulch layer. This action allows the soil to warm up faster, stimulating new growth, and prevents emerging shoots from becoming weak due to lack of sunlight. Managing the mulch layer helps ensure the plant focuses its energy on developing a strong, healthy bulb instead of tender top growth susceptible to late spring frosts.