The potato plant, Solanum tuberosum, is a member of the nightshade family (Solanaceae), which also includes tomatoes and peppers. While the edible potato tuber is a modified underground stem, the plant is a flowering species that reproduces both asexually and sexually. Many gardeners overlook or misunderstand the flowering stage, as the primary commercial crop is grown from tubers rather than seeds. Despite this, the presence of flowers is a significant indicator of the plant’s maturity and its developmental phase.
The Timing and Conditions for Flowering
Potato plants generally begin to flower once they have established sufficient vegetative growth above ground. Flowering typically occurs about six to eight weeks after the seed potato pieces are planted in the soil.
The exact time a plant flowers is influenced by several external factors, including the specific potato variety and local climate conditions. Cooler temperatures and longer daylight hours often encourage the plant to flower. Some modern commercial varieties have been specifically bred to flower sparsely or not at all, to prioritize energy use for tuber growth.
The Biological Purpose of Potato Flowers
Potato flowers represent the plant’s mechanism for sexual reproduction, which is distinct from the asexual propagation used by gardeners. The flowers, which can be white, pink, lavender, or blue, possess both male and female reproductive organs. Successful pollination is necessary for the plant to produce true seeds.
While the cultivated tubers are genetic clones of the parent plant, sexual reproduction through flowers allows for genetic recombination and diversity. This process is primarily used by plant breeders to develop new potato varieties with improved traits like disease resistance or higher yields. For the average gardener, however, the flowers are not required for a successful tuber harvest.
Relationship Between Flowering and Tuber Growth
The appearance of flowers signals that the plant has initiated tuber formation underground. Tuber initiation begins on the stolons, modified underground stems, usually around the same time that flower buds appear, making flowering a useful visual cue for the gardener.
Flowering is not a signal that tubers are ready for harvest, but rather that they are beginning their most active growth phase, known as bulking. Once the plant begins to flower and potentially set fruit, it diverts some energy resources toward seed production, which can slow the rate of starch accumulation in the tubers. For the largest possible harvest, it is best to allow the plant to continue growing for several weeks after flowering, often until the foliage naturally begins to yellow and die back.
The Development and Safety of Potato Fruit
After a potato flower is successfully pollinated, it can develop into a small, round fruit often called a potato berry or seed ball. These fruits typically resemble small, green cherry tomatoes. Each fruit contains numerous tiny, true potato seeds that are used solely for breeding purposes.
The potato fruit is highly toxic and must never be consumed by humans or pets. The fruit, along with the leaves and stems, contains high concentrations of a poisonous compound called solanine, a glycoalkaloid. Ingesting this fruit can cause severe gastrointestinal distress and neurological symptoms. Gardeners should remove and dispose of these potato berries if they appear, especially in areas accessible to children or household animals.