Cilantro (Coriandrum sativum) is a popular annual herb often grown in spring and fall due to its preference for cool weather. Cilantro possesses a natural hardiness that allows it to tolerate mild cold snaps, unlike many other herbs. Understanding the herb’s specific limits is necessary for a successful harvest, especially when unexpected cold fronts bring the threat of frost. The difference between a light frost and a deep freeze dictates whether the plant survives or suffers irreparable cellular damage.
Cilantro’s Specific Cold Tolerance
Cilantro is a cool-season crop that thrives in temperatures between 50°F and 85°F, but it can handle temperatures significantly lower than that. It possesses a tolerance for a light frost, which typically occurs when air temperatures dip to between 28°F and 32°F.
Exposure to cooler temperatures can actually benefit the flavor profile of the leaves. The cold environment prompts the plant to convert starches into sugars, resulting in a slightly sweeter taste. However, this natural hardiness has limits, and cilantro is highly susceptible to sustained hard freezes. A hard freeze is defined by prolonged exposure to temperatures below 28°F, with the absolute lowest tolerance around 20°F. If temperatures drop below this threshold, the water inside the plant’s cells will freeze, rupturing the cell walls and causing fatal damage to the foliage.
Practical Steps for Imminent Frost Protection
Watering Before Frost
When frost is forecast, immediate preventative action is the best defense for cilantro plants. One effective strategy is to thoroughly water the soil around the plants before nightfall. Moist soil retains significantly more heat than dry soil. This stored warmth will radiate upward during the cold night, providing a slight thermal buffer for the plant’s root zone and lower canopy.
Using Physical Covers
Physical coverings are the most reliable method for protecting the above-ground foliage from freezing temperatures. Use specialized horticultural fleece, row covers, or even simple household items like old bedsheets, blankets, or towels. The covering traps the radiant heat rising from the soil and prevents the plant’s surface from cooling to the dew point where frost forms.
Proper Installation
It is important to ensure the covering material does not directly touch the cilantro foliage. Any leaf contacting frozen fabric can suffer immediate cellular damage due to conductive freezing. Use stakes, tomato cages, or other supports to create a mini-tent over the plants, allowing the cover to drape down to the ground. Secure the edges of the material to the ground with rocks or soil to seal in the warmth and prevent wind lift.
Removing Covers
Once the sun has risen and temperatures have climbed above freezing the following morning, the cover must be removed. Removing the cover prevents the plant from overheating, which can cause stress and damage.
Assessing and Managing Post-Frost Damage
Wait until the plant has fully thawed before attempting to assess the damage. Visual signs of frost damage are unmistakable, often appearing as a water-soaked, limp, or blackened appearance on the leaves. The delicate tissues will look wilted and may turn brown or black as the damaged cells collapse.
Do not immediately prune the damaged foliage, as this can shock the plant further. Wait a few days for the full extent of the injury to become clear. Once you can distinguish between healthy and damaged parts, use clean shears to trim away any leaves or stems that are mushy or completely blackened down to the nearest healthy growth point.
If the entire plant, including the central crown and main stem, has turned dark and soft, the growing point has likely been fatally compromised. In this scenario, the plant will not recover and should be removed. However, if the crown remains firm and pale green, the plant may still push out new growth from the center once warmer weather returns.