Chamomile, encompassing the annual German variety (Matricaria recutita) and the perennial Roman variety (Chamaemelum nobile), is a globally cultivated herb valued for its fragrant flowers. The plant’s ability to thrive, produce flowers, and concentrate its medicinal compounds is profoundly dictated by the ambient temperature. Fluctuations outside of a narrow thermal window, from both heat and cold extremes, directly influence the plant’s growth cycles and its ultimate chemical composition.
Ideal Temperature Range for Growth
Chamomile flourishes in climates that offer a mild spring and a moderate summer, favoring a consistent temperature range for vigorous vegetative growth. The optimal daytime temperatures for the plant generally fall between 60°F and 70°F (15°C to 21°C). Maintaining this moderate range promotes maximum foliage development and sets the stage for a high yield of blooms.
If grown indoors, a slightly warmer but consistent range of 65°F to 75°F is maintained to encourage steady development. This preferred temperature zone establishes a baseline for healthy growth, preventing the onset of stress responses.
Chamomile’s Tolerance for Extreme Heat
The plant begins to exhibit signs of thermal distress when ambient temperatures sustain above 85°F (29°C), and its survival is significantly challenged when temperatures exceed 100°F (38°C). German chamomile, in particular, may show visible signs of strain above 95°F (35°C) as its metabolic processes slow down.
Visible signs of heat stress include the leaves becoming a lighter green color, curling inward, or developing scorched patches resembling sunburn. Prolonged exposure to high heat can cause the plant to wilt severely, dry out, and often lead to premature bolting and a shortened lifespan.
To mitigate the damaging effects of intense sun, cultivators often provide light afternoon shade during the hottest hours of the day. Increasing the water supply helps cool the root zone through evaporation, and applying organic mulch assists in maintaining a lower, more stable soil temperature.
Chamomile’s Hardiness to Cold and Frost
Chamomile species possess different degrees of cold tolerance, primarily determined by their life cycle. German chamomile is an annual plant and is the less cold-tolerant variety. While established seedlings can withstand a mild spring frost down to about 30°F (-1°C), the plant will not survive a sustained, deep freeze and is typically planted after the danger of frost has passed.
Roman chamomile is a perennial and demonstrates significantly greater cold hardiness, capable of surviving winters in USDA Hardiness Zones 4 through 8. This species can remain outdoors throughout the winter, entering a dormant state that allows it to successfully overwinter and resume growth in spring. Potted German chamomile, in contrast, must be moved to a protected indoor location to survive freezing temperatures.
Temperature’s Role in Flowering and Oil Production
Temperature has a direct influence on the quality and concentration of the essential oils within the chamomile flower heads. Sustained high temperatures during the growing and flowering period can negatively affect the volatile oil content. While constant warm temperatures around 77°F (25°C) may result in a high number of flowers, the individual flower heads tend to be smaller.
Cooler temperatures, particularly at night, are beneficial for enhancing the quality of the essential oil compounds. A night temperature of approximately 59°F (15°C) yields the highest proportion of chamazulene, the sesquiterpene responsible for the oil’s distinctive blue color and anti-inflammatory properties. Therefore, mild, moderately warm growing seasons are preferred for optimizing the medicinal potency of the final harvest.