Tomatoes, scientifically known as Solanum lycopersicum, are often treated as annual plants, but they are botanically classified as tender perennials. This means they have the genetic potential to live for multiple seasons. However, this perennial nature only expresses itself in continuously warm environments. In most temperate regions, cold temperatures force them into an annual lifecycle.
Understanding the Tomato’s True Nature
The confusion about tomatoes stems from the difference between their botanical classification and their practical application in the garden. As a member of the nightshade family, the tomato is a tender perennial that lives for more than two years under ideal conditions. Its original habitat is the equatorial regions of South America, which lack freezing temperatures.
This warm-climate origin explains the plant’s sensitivity to cold, which prevents it from returning each spring in temperate zones. While tomatoes tolerate temperatures down to about 50°F (10°C), growth slows significantly below this point. Exposure to frost (32°F or 0°C) causes the water inside the plant’s cells to freeze, leading to irreparable damage and death. This biological limitation effectively converts the perennial into an annual for gardeners outside of frost-free regions.
Methods for Overwintering Mature Plants
To keep a mature plant growing for a second season, the root system must be preserved indoors by forcing the plant into semi-dormancy. This process begins before the first expected frost by selecting a healthy plant free of pests and diseases, and pruning it severely.
Pruning and Repotting
The plant should be cut back to a manageable size, leaving only one to two feet of the main stem and a few healthy branches. Remove all flowers and developing fruit so the plant focuses its energy on survival rather than reproduction. If the plant is in the ground, carefully dig it up and repot it into a container, preserving as much of the root ball as possible.
Indoor Care
Move the potted plant to a cool, non-freezing indoor location, such as a basement or heated garage. Temperatures should remain consistently between 55°F and 65°F (13°C and 18°C). During this dormancy, light requirements are minimal, and watering must be drastically reduced. The soil only needs enough moisture to prevent the roots from completely drying out until the plant can be moved back outside in the spring.
Generating New Plants Annually
Even if the mature plant is not saved, new plants can still be generated from the previous year’s growth through two different methods.
Taking Cuttings
Taking cuttings is the first method and guarantees an exact genetic clone of the parent plant. Tomato stems readily form new roots when placed in water or moist soil, a process that allows a gardener to start a new, smaller plant indoors late in the season. These small, rooted clones can be kept under grow lights throughout the winter and will be much larger than a seed-started seedling when spring arrives.
Volunteer Plants
The second common way tomatoes seem to return is through “volunteer” plants, which sprout spontaneously from seeds of dropped or rotting fruit. Tomato seeds are remarkably cold-hardy and can survive the winter in a dormant state within the protection of the soil.
A key consideration with volunteer plants is that their genetics can be unpredictable, especially if the original plant was an F1 hybrid. Hybrid seeds are the result of a cross between two different parent plants, and the seeds saved from a hybrid will not grow “true to type.” The resulting volunteer plant may produce fruit that is significantly different in size, flavor, or disease resistance compared to the parent, while plants grown from open-pollinated varieties are much more likely to resemble the original.