Growing potatoes from True Potato Seed (TPS) is a specialized approach that differs significantly from planting tuber pieces. TPS refers to the botanical seeds produced by the potato plant’s flowers, which develop inside small, green, tomato-like fruits. This technique is primarily used for breeding new varieties or specific agricultural needs, rather than routine home gardening. Successfully growing potatoes from these tiny seeds requires careful attention to the indoor starting phase and the transition to the garden.
Understanding True Potato Seeds vs. Tubers
Potatoes are typically grown from “seed potatoes,” which are small tubers or pieces of a tuber that serve as clonal propagules. This method of vegetative reproduction ensures the resulting plant is genetically identical to its parent, leading to a predictable and uniform crop. Tuber planting offers faster results and maintains the characteristics of established varieties.
True Potato Seed is the product of sexual reproduction, meaning it carries a high degree of genetic variability. Every plant grown from TPS is genetically unique, making this method ideal for breeding new varieties or selecting for specific traits like disease resistance. TPS is also often free from the soil-borne pathogens and viruses that can accumulate in tuber stock over generations.
Starting True Potato Seeds Indoors
The first step is indoor germination, similar to starting pepper or tomato seeds. True Potato Seeds should be sown indoors approximately six to eight weeks before the last expected frost date. Sowing them too early can cause the seedlings to form tubers before transplanting, which stunts their final growth.
Use a sterile, nutrient-free seed-starting mix in trays or small pots. Press the tiny seeds onto the surface and cover them with about one-eighth of an inch of fine medium. Germination requires consistent warmth, ideally maintaining 70 to 75°F until the seedlings emerge, which typically takes seven to fourteen days. Once sprouted, they need immediate, high-intensity supplemental light for 14 to 16 hours daily to prevent them from becoming tall and spindly.
The fragile seedlings should be “pricked out,” or transplanted, into slightly larger individual containers once they develop their first set of true leaves. This provides the developing root system with more space. The plants can tolerate a slightly cooler environment, but they must continue to receive strong light to develop a sturdy stem before moving outdoors.
Transplanting and Maintaining Seedling Growth
Before the seedlings are permanently set out in the garden, they must undergo hardening off to acclimate them to the outdoor elements. This involves gradually exposing the plants to direct sunlight, wind, and cooler temperatures over seven to ten days. Start with a few hours in a shaded, protected area, slowly increasing the duration and intensity of exposure each day.
When transplanting, the outdoor soil temperature should consistently be above 45°F, with the daily high temperature above 55°F. Plant the seedlings deep, burying the stem up to the top set of leaves. This encourages a strong root system and future tubers along the buried stem. Spacing can be tighter than with tuber-grown potatoes, with some growers using as little as eight inches between plants for smaller tubers.
Consistent water is necessary for these young plants, as they are establishing roots and cannot tolerate drying out. Hilling, the practice of mounding soil around the base of the plant, protects developing tubers from light and encourages further growth. Hilling should begin when the plants are four to six inches tall and repeated as the plants grow taller throughout the season.
Harvesting and Seed Saving Considerations
Potatoes grown from True Potato Seed will typically be ready for harvest later than those grown from conventional tubers, usually requiring 90 to 120 days from transplanting. Tubers are maturing when the plant’s foliage naturally begins to yellow and die back. Due to the genetic diversity inherent in TPS, the resulting tubers will be highly variable in size, shape, and color.
The primary goal for many who grow from TPS is selection and breeding, since every plant is unique. To stabilize a new variety, select the best-performing plants based on criteria like tuber yield, disease resistance, and flavor. Save several desirable tubers from these selected plants to use as seed potatoes the following year.
If the goal is continued breeding, you can collect the actual botanical seeds from the green, cherry-tomato-like fruits that form on the potato plant after flowering. These fruits must be allowed to ripen fully, often until they soften or drop from the plant. The tiny seeds are then extracted and dried for long-term storage. Saving the seeds allows for continued experimentation and the potential discovery of a unique, locally adapted potato variety.