As temperatures gradually fall across Missouri, frost is expected within the next two weeks in the northernmost parts of the state, according to the University of Missouri Extension’s Frost/Freeze Probabilities Guide. This serves as a timely reminder for gardeners to prepare their plants for the colder weather, said MU Extension state horticulture specialist David Trinklein.
Although freezing temperatures are not yet in the forecast, daily temperatures are steadily dropping by about one-half degree, while daylight is decreasing by 2-3 minutes per day, noted MU Extension state climatologist Zachary Leasor. Frost dates vary across Missouri, with the first frosts expected in northern counties in about two weeks, around Oct. 20 for central Missouri, and near Nov. 1 in the southern part of the state. Higher elevations, such as the Ozarks, may experience frost earlier.
“Not all plants react the same to lower temperatures,” Trinklein said. “Tropical plants, in particular, suffer ‘chill injury’ at temperatures well above freezing, and they should not be exposed to temperatures below 45 degrees Fahrenheit.” Many of these plants are grown in containers and should be brought indoors as early as possible to prevent damage.
Trinklein also explained that the moisture in plant tissue differs from pure water and does not freeze at the typical 32 degrees Fahrenheit. Most plants, except for sensitive tropical species, can tolerate temperatures as low as 28 degrees Fahrenheit with minimal damage. Certain cool-season flowers and vegetables can endure even lower temperatures, especially when gradually exposed to cooler conditions.
For fall gardening, Trinklein noted that protecting plants from the cold is often about delaying the inevitable. “Whether it’s ornamental plants or food crops, they’ve served their purpose throughout the growing season,” he said. In contrast, spring protection aims to safeguard an investment in plants that are expected to grow and yield results, which may require more extensive measures.
To protect plants from cold temperatures in either season, the goal is to preserve the latent heat stored in the soil or containers. Using insulating materials, such as floating row covers, can help protect plants by creating a small difference in temperature beneath the insulation, however, in the fall, there tends to be more latent heat in the soil, making frost protection somewhat more effective. Gardeners are encouraged to remove any protective coverings during the day to allow the plants to receive direct sunlight.
As the growing season draws to a close, many gardeners may choose to follow the natural rhythm of the seasons, accepting the end of the planting cycle and preparing for winter. “To everything, there is a season,” Trinklein concluded, reminding gardeners to look ahead to the next planting season with optimism.
