Arugula, sometimes called rocket, is a peppery green and a member of the Brassica family. Classified as a cool-season crop, it thrives in the milder temperatures of spring and fall. This allows arugula to tolerate temperatures far lower than many other common salad greens. Understanding its specific temperature limits is essential for a continued harvest.
Arugula’s Baseline Cold Tolerance
Arugula produces its best flavor and most tender leaves when the air temperature falls within the range of 45°F to 65°F (7°C to 18°C). This cool environment is optimal for growth without triggering the plant to prematurely “bolt,” or go to seed, which is a common reaction to prolonged heat. Exposure to light cold temperatures actually improves the culinary quality of the leaves.
The cold air triggers a physiological response in the plant that increases the sugar concentration within its cells. This higher sugar content functions as a natural antifreeze, lowering the internal freezing point of the plant’s tissues. Arugula harvested after a touch of cold weather is often noticeably sweeter and less bitter than plants grown during warm periods.
Freezing Point Thresholds and Plant Damage
Arugula can survive short periods of light frost, defined as temperatures that drop to between 28°F and 32°F (0°C to -2°C), without sustaining permanent damage. The plant’s cell structure is robust enough to handle the initial shock of freezing, especially if the plants have been gradually acclimated to the cold. However, the danger begins when temperatures consistently drop lower than this range for several hours.
A temperature below 25°F (-4°C) is considered a hard freeze and is the point where significant damage occurs to the plant tissue. At this threshold, the water inside the plant cells expands as it freezes, rupturing the cell walls. This internal damage causes the leaves to turn dark and mushy upon thawing, a clear sign of tissue death.
While the foliage may be destroyed, the survival of the entire plant depends on the condition of the crown and the root system. If the central growing point remains unfrozen, the arugula can often produce new leaves once warmer conditions return. However, the average garden arugula will not survive deep cold without protection.
Strategies for Protecting Arugula from Hard Freezes
When temperatures are forecast to dip below the 25°F threshold, gardeners can employ several methods to insulate their arugula patch. The most immediate and effective measure is to cover the plants with a physical barrier. Floating row covers, frost cloths, or even old bed sheets can be draped over the plants to trap residual ground heat and block wind. It is important to ensure this covering does not directly touch the foliage, as this can transfer the cold and cause localized damage.
A layer of organic mulch, such as straw or shredded leaves, can be applied around the base of the plants to insulate the soil and keep the root zone warmer. Watering the plants thoroughly before a deep freeze is also effective, as moist soil retains heat better than dry soil, providing a thermal buffer for the roots. These protective measures create a microclimate that can raise the ambient temperature by several degrees, often preventing frost damage.