Saving seeds from a plant's flowers or fruit is a very common method of propagating new plants, but it can be more complicated than you think, especially for some vegetables, such as cucumbers. Cucumbers are among those species that have distinctly different male and female flowers, and thus they fertilize by cross-pollination rather than self-pollination. This means that hybrid plants require some special handling if you plan to save the seeds.
Before You Get Started
Many commercially produced cucumber seeds are harvested from newly developed hybrids (often labeled F1), which are produced each season by carefully controlling the fertilization between distinctly different varieties of cucumber. The goal of this cross-breeding is to produce a hybrid plant with special desirable characteristics, but these qualities are often lost in the next generation of the F1 plant, when uncontrolled cross-pollination enters the story. All too often, the F1 plant you grow gets cross-pollinated by pollen from an unknown variety of cucumber somewhere in the area. As a result, the seeds in the fruit, if planted, may produce new generation fruit that is very, very different from what you expect.
But this is generally a problem only for newly developed hybrids developed by controlled pollination. It's not an issue for older cucumber varieties that are long since past their initial controlled hybridization. For this reason, the best cucumbers to grow if you want to collect and replant seeds are older varieties, many of which are known as heirlooms. Most, though not all, heirlooms are open-pollinated plants, fertilized by uncontrolled cross-pollination. With heirloom (and some older non-heirloom hybrids) seeds collected from their fruits will reliably produce plants nearly identical to the parent plant.
But if you are intent on saving seeds from a newer hybrid, experts recommend making sure that no other varieties of cucumber are growing within half a mile. This ensures that pollination is more likely to occur between the male and female flowers on the same plant, not an outsider. Another method of controlling pollination is to enclose the plant's flowers within netting to reduce the chances that pollen from an unknown variety can fertilize them.
What Is an Heirloom Variety?
The term "heirloom" is often applied to plant varieties—especially vegetables—that have been in constant cultivation for a long time. There is disagreement over how old a plant variety must be to earn the heirloom label, but some experts consider 1951 to be the dividing line between modern and heirloom varieties. The genetic history of heirloom plants is often complicated, and the exact lineage is rarely known. Heirloom plants are often quite different than modern hybrids since they are open-pollinated plants that don't require hand pollination.
When to Collect Cucumber Seeds
Cucumber seeds are not ready to harvest until the fruits are completely ripe, well past the point where you usually harvest cucumbers for eating. Leave the fruits on the vine until they are fully yellow or tending toward orange before you harvest them for seeds.
Equipment / Tools
- Small artist's brush
- Small bowl
- Spun mesh bags (hybrid cucumbers only)
- Storage bag or mason jar
Isolate the Plant (Hybrid Varieties)
If you are trying to save cucumber seeds from a modern hybrid variety, the first step is to isolate your plant before it fruits. To do so, identify which blossoms are female by looking for a tiny cucumber-like structure at the base of the flower. Once you've identified the female blossoms, you can bag them individually in spun polyester or cotton bags, which will prevent insects from cross-pollinating them—possibly with pollen from an undesirable plant. One cucumber fruit can produce hundreds of seeds, so it's not necessary to identify and tag all the flowers—only the ones you want to develop into fruit for seed-saving.
Follow the same process with some adjacent male flowers, making sure to tag the bags.
Another (more in-depth) way to isolate your cucumber plant involves building a cage to enclose the entire plant. Typically made using a wood or PVC frame that's been covered in a spun polyester screen, such a DIY device also works great to keep pollinators out.
Hand-Pollinate the Flowers (Hybrid Varieties)
You don't want insects pollinating the hybrid cucumber plants you'll be saving seeds from, so this is the part where you play Mother Nature yourself. To pollinate the flowers you'll harvest for seeds, first use a small brush to collect the pollen from a bagged male cucumber flower. Then, gently place the pollen onto the stigma in the center of the bagged female flowers.
Re-bag the female blossom until it begins to ripes into a fruit—not only is that a great reward for all your hard work, but the presence of a cucumber assures that your hand-pollination methods worked. At this point you can safely remove the bags from all your cucumber plants—just make sure you keep the female fruit tagged so you remember to harvest it for seed and it doesn't end up in a salad by mistake.
Grow Fruit to Maturity
Any cucumbers being cultivated for seed must be grown to full maturity and remain on the vine past the point where they're no longer edible. You'll notice that the cucumber will be larger than its usual harvest size and will start to soften on the vine—it may also change in color from green to yellowish or orange, another good indication that it's time to harvest. It's important to keep an eye on the cucumbers you'll be harvesting throughout the season to ensure they don't look like they're diseased in any way.
Harvest the Fruit and Separate the Seeds
To harvest the fruit and collect the seeds, you'll want to follow a few simple steps. First, pick the cucumber from the vine using either your hand or pruners if the vine is too thick. Bring it inside, then cut it lengthwise to reveal its inner seeds. Scoop the pulp contents into a small bowl or mason jar, then add enough room-temperature water to cover the pulp and seeds, which will help remove their gel coating.
Similar to saving tomato seeds, you'll want to set the container aside (uncovered) in a warm spot that ideally maintains a temperature between 70 degrees Fahrenheit and 80 degrees Fahrenheit. Stir the mixture daily. Once approximately three days have passed, you'll notice that some of the seeds have begun to sink to the bottom of the container. This is a good indication that fermentation is occurring, which further rids the seeds of their gel coating and separates poor seeds (the floating seeds) from the viable ones (the sunken seeds).
Clean and Store the Seeds
Once all (or most) of the seeds have sunk, add additional water to the container to clean them. Any debris or unviable seeds will again float to the top, making them easy to skim off and discard. Rinse the good seeds a few more times, then strain them and place them on paper towels to dry. Once dry, store the seeds in an air-tight storage bag or a Mason jar and label them for next year's sowing. If stored properly, your cucumber seeds will remain viable for 10 years.