There are many methods you can use to ensure a prosperous garden each year, and saving seeds from heirloom or open-pollinated varietals is a wonderful way to almost always guarantee a plant's vitality. By selecting seeds from plants with the best qualities, you can tailor the specific conditions in your garden, allowing for a fruitful harvest for years to come.
However, no two fruits or vegetables are alike, so when it comes to saving seeds, each varietal is different. Take cucumbers, for example. They need to be pollinated by insects or the wind (or hand-pollinated by the gardener) in order to set fruit. To complicate things even further, cucumbers cross-pollinate easily with other cucumber varieties, which can impact the success of future harvests. Professional seed savers recommend separating cucumber varieties by at least half a mile when planting in order to prevent crossing.
Since most home growers don't operate large-scale farms with that much available space, isolation for cucumber seed collection requires a few nuanced measures, following by pollination and finally harvesting.
Isolate the Cucumber Plants
The first step to saving cucumber seeds is to isolate your plant before it fruits. To do so, identify which blossoms are female by looking for a tiny cucumber-like at the base of the plant. Once you've identified the female blossoms, you can bag them individually in spun polyester or cotton bags, which will prevent insects from pollinating—and therefore crossing—them. Follow the same process with the adjacent male flowers, making sure to tag the bags that contain the female blossoms so you can easily identify them later as the ones you'll harvest for seeds.
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, the DIY device also works great to keep pollinators out.
Hand-Pollinate the Cucumber Flowers
You don't want bees pollinating the 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 female flower.
Re-bag the female blossom until it ripens 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.
Harvest the Cucumber Seeds
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 slightly in color from green to yellowish, 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.
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 a pair of gardening sheers 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).
Once all (or at least the majority of) your 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.