Garlic, a staple in kitchens worldwide, requires specific temperature conditions throughout its life cycle, from planting to post-harvest storage. Understanding these thermal tolerances is important for growers to achieve a robust harvest and for consumers to extend bulb shelf life. Managing environmental temperatures is key for successful cultivation and preservation.
Temperature Needs for Growing Garlic
Garlic’s growth cycle is linked to temperature fluctuations, requiring distinct temperatures at different stages. This ensures proper development from a single clove into a multi-cloved bulb.
Cold Requirement for Growth
Garlic, particularly hardneck varieties, needs a period of cold exposure, known as vernalization, to stimulate bulb formation. This chilling period requires temperatures below 40-50°F (4-10°C) for 6 to 12 weeks. Without sufficient vernalization, garlic cloves may not divide into distinct bulbs, resulting in a single, undivided bulb or no bulbing. This cold treatment can occur naturally with fall planting in colder climates or can be artificially induced by refrigerating planting stock.
Optimal Temperatures for Leaf Growth
After vernalization, spring brings a period of vegetative growth, developing leaves and roots. Garlic shoots can tolerate temperatures down to 20°F (-6°C) without damage. Root growth occurs whenever the ground is not frozen, and top growth begins when temperatures rise above 40°F (4.5°C). Consistent, moderate spring temperatures encourage strong plant development, essential for later bulb enlargement.
Warmth for Bulb Formation
As days lengthen and temperatures rise in late spring and early summer, garlic transitions from vegetative growth to bulb formation. Bulb initiation is triggered by increasing daylight (over 13 hours), and soil temperatures above 60°F (15.5°C) and air temperatures above 68°F (20°C). This warmth signals the plant to redirect energy from leaf production to bulb swelling. Excessive heat during this phase, however, can lead to smaller bulbs or premature dormancy.
Protecting Garlic from Temperature Extremes
Managing temperature extremes is important for successful cultivation, as prolonged cold and intense heat negatively impact plant health and bulb development. Proactive measures can help mitigate these risks.
To protect garlic from severe winter freezes, applying a thick layer of mulch is a common practice. A 4 to 8-inch layer of organic material like straw or shredded leaves insulates the soil, maintaining a consistent temperature around the cloves. This mulch layer also prevents frost heave, which occurs when freezing and thawing soil pushes cloves out of the ground. Adequate drainage also prevents waterlogging, which can lead to rot in cold, wet conditions.
During periods of high heat, especially during bulb formation, garlic plants can experience stress. Temperatures exceeding 80°F (27°C) in the month prior to harvest can negatively affect dormancy and storability. In hot climates, partial shade can reduce plant heat stress. Consistent soil moisture through adequate watering also helps plants cope with elevated temperatures, as drought stress exacerbates heat effects.
Storing Garlic at the Right Temperature
After harvest and proper curing, maintaining the correct temperature is important for extending garlic’s shelf life and preventing sprouting or spoilage. Cured garlic stores best in cool, dark, and well-ventilated conditions.
The optimal temperature range for long-term storage is between 55°F and 65°F (13-18°C). Temperatures below 50°F (10°C) can cause garlic to sprout. Conversely, temperatures consistently above 70°F (21°C) can lead to dehydration and quicker deterioration. Relative humidity of 45-60% helps prevent drying out, mold, or root development. Good air circulation, often with mesh bags or open containers, prevents moisture accumulation and stagnant air.