New gardeners often ask whether it’s alright to plant cucumbers, squash, or gourds next to each other. Their concern is whether cross-pollination will result in inedible fruit. Fortunately, the pollen source does not affect the current season’s fruit. However, if the seed from that cross-pollinated fruit is saved and planted the following year, the resulting plants can be very different, and may be inedible. (Gourds produce a toxin that is bitter, so if you have a squash that is bitter, discard it and remove the plant from the garden.)
Seed Saving Precautions
Saving seed from garden vegetables can be rewarding, but it also comes with challenges, especially with plants that are cross-pollinated.
If gardeners wish to save seed from cucurbits (squash, pumpkins, gourds, cucumbers, and melons), special precautions need to be observed, as these plants are insect-pollinated. Additionally, they have separate male and female flowers, which increases the chances that the female flower may be fertilized with pollen from a different variety of the same type or species. Unless you (and nearby neighbors) have grown only one of the types or varieties, you could end up with some very strange vegetables from seed saved from those plants.
Plants from within the following groups will cross with each other:
- Zucchini, Yellow Crookneck, Acorn, Spaghetti, Patty Pan, Delicata, Pumpkins and Gourds (except edible snake gourds) all may cross with each other.
- Butternut, Buttercup, Banana, Hubbard and Turban squashes may cross with each other.
- Muskmelon, Cantaloupe, Charentais; Honeydew; Casaba; Armenian Cucumber; Snake melon (gourd) can all cross with each other, but not with squashes, pumpkins, or cucumbers.
- The Buffalo gourd, a weed, is too distantly related to cultivated species to be a problem.
Cucumbers, watermelon, and Loofah gourds only cross only with themselves, so you don’t have to worry about isolating them unless you are growing several varieties of the same type.
To prevent cross-pollination between compatible types or varieties, they need to be separated by a distance of one-half to one mile. The presence of barriers such as large buildings, a thick stand of trees, or a hill can inhibit pollinator movement and allow for shorter isolation distances. However, since most gardeners don’t have adequate distance from other gardens or squash varieties within their own garden, the alternative is to (1) net or cage the entire plant to exclude insects or (2) bag or tape shut new male and female flowers as they are forming (before they open, but just beginning to show a bit of yellow or orange color) to prevent insect transfer of pollen. These methods require hand-pollination of the flowers. Early in the morning, a small paintbrush can be used to collect pollen from a male flower, and transfer it to a female flower. For best results, this should be done as soon as the female flower (identified by the miniature fruit just below the petals) first opens, within 4 hours of opening. Rebag or retape the female flower shut after you have pollinated it. Once you have fruit set, you can remove all the bags – just be sure to mark the fruit that you hand-pollinated.
Because pollen from the same plant can pollinate a flower, you only need to plant a single cucurbit plant in order to harvest viable seeds. However, to maintain a variety over time, save seeds from between 5-10 plants. If you’re saving seeds for genetic preservation of a rare variety, save seeds from 25 plants.
Seed Processing for Cucurbits
Pick fruit several weeks after it has matured to the point of changing color to yellow or orange. Scoop out the seeds and surrounding pulp, and place into a container, add water and let ferment 2-4 days at room temperature, stirring occasionally. Add more water, stir, and allow the nonviable seeds and pulp to float to the top, where they can be removed. Repeat if necessary to thoroughly clean the seed. When clean, spread seeds out to dry on coffee filters, paper towels, or screens. When sufficiently dry, they can be cleanly snapped in half.
For best results, store the fruit until it begins to lose eating quality; then ferment as above. Summer squash should be left on the plant until the rind hardens, then processed as above.
Allow fruit to remain on the plant for 1 to 2 weeks after maturity; alternatively, harvest reipened fruit and allow it to set for a few days prior to harvesting the seed. The seed can be simply washed by hand and then dried.
Once completely dry, seed should be stored in a cool dry location. If you have room, storing in your refrigerator is ideal. Make sure the storage containers are completely dry. Envelopes or ziplock bags work fine, as well as baby-food jars, etc. Most seed will stay good for at least 3-4 years. Don’t forget to label everything with both the plant name and date!
An Additional Caution
Some diseases can be spread through seed from infected plants. Following is a list of some of the diseases that can be spread through seed:
- All Cucurbits
- Angular Leaf spot (especially cucumber)
- Gummy stem blight
- Squash mosaic virus
- Muskmelon, Cucumber, Watermelon
If you know that your plants have any of these diseases, you should not save the seed. However, most people will have no idea whether their plants are infected with particular fungi, bacteria, or viruses. A good rule of thumb is to simply save seed only from plants that have healthy, normal-looking leaves and fruit.
For further reference:
- Seed Saver’s Exchange. 3076 North Winn Road; Decorah, IA 52101; Phone: 319-382-5872
- “The Organic Seed Grower” by John Navazio. 2012. Chelsea Green Publishing, White River Junction, VT.
- “The Manual of Seed Saving: Harvesting, Storing, and Sowing Techniques for Vegetables, Herbs, and Fruits” by Andrea Heistinger 2013. Timber Press, Portland, OR.