Late October can be a somber time of the year for gardening enthusiasts, since it usually signals the end of the outdoor growing season, said University of Missouri Extension horticulturist David Trinklein.
Based on decades of weather data, there is a 50% chance that mid-Missouri’s first frost of fall will happen on or before Oct. 23, and a 70% that first frost will arrive by Oct. 29. In any case, the end of the growing season is near.
Plants differ in their ability to withstand cool weather. Some species, mainly tropical plants, suffer “chill injury” at temperatures well above freezing. Most species in this category should not be exposed to temperatures lower than 45 F. Container-grown tropical houseplants placed outside for the summer should be brought inside early in the fall, if possible.
Another consideration is that the moisture in plant tissue is not pure water; it contains solutes that lower its freezing point. Except for sensitive tropical plants, most plants can withstand 28 F with little, if any, damage. Cool-season flowers and vegetables (pansy and cabbage, for example) can withstand considerably lower temperatures, depending on species and the exposure to gradually cooler temperatures.
Protecting plants in the fall differs from spring protection. In the fall, gardeners are “prolonging the inevitable.” Whether it is ornamentals or food crops, most have served their purpose and provided enjoyment and food for the past growing season. In the spring, gardeners are protecting an investment they have made in plants that have yet to yield dividends, so more aggressive (and expensive) measures are warranted.
In either case, protection from cold usually involves preserving latent heat stored in the soil of a garden or growing medium of a container. Usually, this entails placing insulating material over tender plants. However, this process likely will result in a difference of only a couple of degrees. Lightweight floating row cover (such as Agfabric) is an example of a commercially available product for frost protection. Bed sheets, blankets or other items already on hand may be used, but a support mechanism may be needed to keep these materials from crushing delicate plants.
Fortunately, the soil contains more latent heat in the fall than in the spring, so protecting plants with an insulation tends to be more successful in the fall. Unless cold temperatures continue throughout the day, remove insulation during the day to expose plants to sunshine.
However, there comes a point late in the year when gardeners must acknowledge the growing season has ended, said Trinklein. “While it can be difficult to watch delicate flowers and tomato plants heavy with fruit succumb to the first autumn frost, this transition is a natural and necessary part of the Earth’s cycle. Resisting the change only leads to frustration, whereas embracing it allows gardeners to concentrate on essential autumn tasks like harvesting the garden’s final vegetables, clearing spent beds and planting cover crops.”
Finally, don’t be discouraged. As writer and naturalist Hal Borland wrote, “No winter lasts forever, and no spring skips its turn.” The 2027 growing season is just around the corner.
By Linda Geist, University of Missouri Extension
