In urban settings where isolation distance cannot be used as a method for squash seed saving, hand pollination and individual flower isolation is required to save true-to-type seeds from crops commonly called squashes, zucchini, and pumpkin. This is because cucurbitaare pollinated by insects who can carry pollen up to half of a mile, crossing members of the species mazima, moshata, pepo and argyosperma.
Ahead of time
- Observe what squash blossoms look like the evening before they open for the day. Petals on tomorrow’s flowers will be almost full-sized, showing some orange-yellow color, but still closed tight.
In the evening
- Observe differences between male and female flowers, and identify some of each that will open the next morning. Male flowers are attached to longer flower stems. On female flowers, an enlarged ovary can be seen just below the petals. It looks like a tiny squash. Tie shut or put spring-loaded clips on the female flowers and about three male flowers for each female. Try to find them from multiple plants of the same variety if possible so you are crossing two plants of the same variety.
The next morning
- Cut the male flowers off the plants and tear off the petals to expose the pollen-holding anthers. Gently open the female flowers (because you will seal the petals back up) and, working quickly, brush pollen from three male flowers on the stigma of the female flower. Keep pollinators away, and if one gets to any of the flowers you are working with, abandon those for seed saving.
- Once you’ve pollinated a female flower with pollen from there male flowers, seal it up with masking tape or something similar. If the petals are tattered, use a scrap of cloth or lots of tape to ensure the flower is completely closed up to prevent contamination by pollinators. Mark that flower stem loosely with a bright ribbon or something to remind yourself not to harvest that squash until it is fully mature at the end of the season. For summer squashes, this will be long after you’d harvest for eating.
At the end of the season
- When the squash is fully mature, the stem leading to it will be dry or starting to dry, and the skin will be too thick and tough to dent with a fingernail. You’ll probably leave it out until close to a frost. After cutting it off the vine, crack it open and scoop the seeds into a colander. Wash seeds to remove pulp and its sugars with would otherwise mold. Spread on screen, paper, or colander to dry completely before storing.