Borage (Borago officinalis) is a popular annual herb recognized for its culinary, medicinal, and ornamental attributes. This plant features distinctive star-shaped blue flowers and leaves covered in a bristly texture. Understanding its environmental needs, particularly temperature, is important for ensuring its successful growth and vibrant display in any garden.
Borage Temperature Tolerance
Borage thrives in moderate temperatures, with an optimal range for growth and flowering typically between 60°F and 75°F (15°C to 24°C). Some sources suggest a slightly broader preferred range of 68°F to 100°F (20°C to 38°C), indicating its adaptability. Temperatures around 65°F to 70°F (18°C to 21°C) are especially favorable for seed germination and the development of healthy seedlings.
The plant exhibits a degree of cold tolerance, capable of withstanding light frosts. However, borage is an annual herb and typically dies back when subjected to a hard or killing frost. While mature plants can endure short periods at temperatures as low as 50°F (10°C), prolonged freezing temperatures below 32°F (0°C) are generally detrimental.
Borage also shows tolerance to warm conditions, though extremely high temperatures can impact its vigor. When temperatures consistently exceed 80°F (27°C) in the shade or reach above 100°F (38°C), the plant’s growth and flowering can be affected, and it may not bloom as prolifically. Above 110°F (43°C), leaves may lighten in color, curl, become susceptible to sunburn, and the plant may wilt or dry out.
Cultivating Borage in Varying Temperatures
Successful borage cultivation involves strategic planting and environmental management to accommodate its temperature preferences. Direct sowing of borage seeds is often recommended, as the plant develops a taproot that can make transplanting difficult. The ideal time for outdoor planting is in early spring, after the last threat of frost has passed and when soil temperatures have warmed to at least 60°F (15.56°C). In regions with milder winters, fall planting can also be successful, allowing for winter and spring growth.
Protecting borage from unexpected late frosts is important for young plants. While seedlings can survive light frosts, applying mulch around the base of ground-planted borage or using horticultural fabric can create an insulated barrier against cold wind and frost. If borage is grown in containers, moving them indoors to a location with bright, indirect light can safeguard them from freezing temperatures below 15°F (-10°C).
Managing borage during hot spells involves several techniques to mitigate heat stress. Providing partial shade, especially during the hottest parts of the day, can help prevent sunburn and wilting. This can be achieved by selecting planting locations that receive morning sun and afternoon shade or by using shade cloth. Adequate watering is also important in warm conditions, as borage does not tolerate drought, particularly when young. Watering deeply to keep the soil consistently moist, especially for container-grown plants, can support the plant’s health and encourage continued flowering.