Seed saving involves preserving genetic material from cultivated plants to ensure a sustainable supply for future seasons. Squash, a member of the Cucurbita genus, is a particularly rewarding plant for this practice due to the large, easily handled seeds it produces. By saving seeds, gardeners can select for traits like improved flavor, better adaptation to local soil and climate conditions, and greater disease resistance over time. This process allows the gardener to participate directly in the evolution and preservation of their favorite varieties. Understanding a few fundamental botanical rules is the first step toward successfully harvesting viable seeds for next year’s garden.
Selecting the Best Parent Squash
The process begins with selecting the appropriate fruit from which to harvest seeds, which must come from an open-pollinated (OP) variety, not a hybrid (F1) variety. Open-pollinated seeds produce plants that are true-to-type, meaning the offspring will closely resemble the parent plant. Seeds saved from a hybrid squash, however, will result in an unpredictable mix of traits in the next generation, often leading to undesirable or inedible fruit.
The chosen squash fruit must be fully mature, which is often well past the stage where it would be harvested for eating. For winter squash varieties like butternut or pumpkin, this means the skin should be hardened and difficult to pierce with a fingernail. Summer squash varieties, such as zucchini, need to be left on the vine until they swell to a massive size and their skin becomes tough. Saving seeds from plants that demonstrated the best characteristics throughout the season helps improve the quality of the seed stock. Select fruit from multiple healthy parent plants, ideally between five and ten, to maintain a broad genetic diversity within the saved seed lot.
Preventing Cross-Pollination and Hybridization
Maintaining varietal purity is the greatest challenge when saving squash seeds because the plants are insect-pollinated out-breeders. All cultivated squash fall into distinct species groups, with the most common being Cucurbita pepo (acorn, zucchini, spaghetti), C. maxima (Hubbard, buttercup), and C. moschata (butternut, tromboncino). Varieties will easily cross-pollinate with any other variety within the same species group, resulting in mixed genetics in the seeds.
A zucchini (C. pepo) planted near an acorn squash (C. pepo) will cross, but neither will cross with a butternut squash (C. moschata). The resulting fruit on the current plant will still look and taste like the parent variety, but the seeds inside carry the mixed genetics that will produce an unexpected “squash-mutt” if planted next season. To prevent this, a seed saver must isolate varieties within the same species by a significant distance, often a quarter-mile, which is impractical for most home gardens.
A more practical solution is to only grow one variety from each species, or to employ hand-pollination techniques. Hand-pollination involves covering the female flower (which has a miniature fruit behind it) and the male flower (on a thin stem) the evening before they open. The next morning, the pollen from the male flower is transferred directly to the female stigma, and the female flower is immediately re-covered and tagged to prevent insect cross-pollination. This ensures a controlled parentage for the fruit destined for seed saving.
Step-by-Step Seed Extraction and Cleaning
Once the parent squash has reached full maturity, the process of seed extraction can begin. Cut the squash lengthwise, being careful to avoid slicing through the central seed cavity and damaging the seeds themselves. The seeds, along with the surrounding pulp and stringy material, should be scooped out into a non-metal container, such as a large bowl or bucket.
The next step is to remove the gelatinous coating that surrounds each seed, which contains germination inhibitors and can harbor disease. This is achieved through a wet-processing method known as fermentation. The scooped pulp and seeds are covered with water and allowed to sit at room temperature for one to four days, depending on the ambient temperature.
During the fermentation period, the pulp begins to break down, and any non-viable seeds or debris will float to the surface. Viable seeds are denser and will sink to the bottom of the container. After fermentation, the floating material is carefully poured off, and the sunken seeds are rinsed thoroughly under cool running water until they are completely clean of all residue. Clean seeds should feel slightly rough to the touch, and any seeds that continue to float after the cleaning process should be discarded as they are unlikely to germinate.
Drying and Long-Term Storage Requirements
After cleaning, the seeds must be dried completely to reduce their moisture content for long-term viability. The goal is to reduce the internal moisture content to below eight percent, which slows the metabolic processes within the seed and prevents mold growth during storage. The cleaned seeds should be spread out in a single layer on a non-porous surface, such as a fine mesh screen, a ceramic plate, or a glass dish.
Avoid using paper towels, as the seeds may stick firmly to the material once dry. Place the drying seeds in a warm, dry area with good air circulation, away from direct sunlight or artificial heat sources, which can damage the seed embryo. Stirring the seeds once or twice a day will promote even drying, which can take anywhere from one to three weeks depending on the humidity.
Once the seeds are dry, they should feel hard, slide easily against each other, and snap rather than bend. For storage, use an airtight container, such as a sealed glass jar, or a simple paper envelope. Store the container in a cool, dark, and dry location, like a refrigerator or a dark pantry, as low temperature and low humidity are the two factors that maximize seed longevity. Labeling the container with the variety name and the date of harvest ensures accurate tracking for planting in the subsequent season.