|Species joined by a solid line do not cross, but crossing may occur between species connected by a broken line.|
One of my friends has started a large CSA (Community Supported Agriculture) this year, and the subject of saving seeds came up. Obviously, if you can save seeds from OP (open pollinated) and/or heirloom varieties, you can save some money the following year by not having to purchase seeds again. However, some vegetables are notorious for cross-pollinating, like peppers and squash. Commercial pepper farms isolate varieties by 1500 feet, which isn't practical for CSA's or the home gardener.
Beans (P. vulgaris) rarely cross naturally, but lima beans (P. lunatus) and runner beans (P. coccineus) will. Tomatoes will cross, although it's hard for insects to actually get to the pollen. You can isolate varieties by a trap crop (like peppers) between them. With any vegetable saved for seeds, save only the very best, and save several of the same variety mixed together, even mix with a few of the original seeds if they are only a year or two old. ALWAYS save enough of the original seed to plant out the following 2 years in case of a crop failure.
Any vegetable that cross-pollinates will still grow the first year just as it is supposed to do, but any saved seeds will likely produce some strange looking veggies the following year. Here's a lesson on cross pollination on the Curcurbit family, and down below that, a tip on how to easily isolate seeds so they do not cross pollinate.
To be honest, this information is most likely copied word for word from someone's site on the internet, but I've had it in my files for ages, with no source listed. It may even be copyrighted material and I apologize, but I'm just using it for education, which is allowed by law.
Plants in the Cucurbitaceae or gourd family belong to four species among which crosses may occur. The success of such crossing depends on the species to which a variety belongs. Plants belonging to the Cucurbitaceae family produce separate male and female blooms on the same plant. Insects are usually required to cross-pollinate blooms.
This refers to the drawing above: Species joined by a solid line do not cross, but crossing may occur between species connected by a broken line.
The more common varieties of gourd, pumpkin, and squash belong to the species indicated below:
C. pepo: Casserta, Cocozefle, Connecticut Field, Delicata, Early Prolific Straightneck, English Marrow, Golden Custard, Orange Gourd, Pea, Gourd, Small Sugar, Table Queen or Acorn, Tours, Tricolor Spoon Gourd, Uconn, White Bush Scallop, Winter Luxury, Yellow Crookneck, and Zucchini.
C. moschata: Alagold, Butternut, Calhoun, Chirimen, Dickinson Field, Golden Winter Crookneck, Kentucky Field, Large Cheese, Sugar Marvel, and Turkish Honey.
C. mixta: Green Striped Cushaw, Japanese Pie, Silverseed Gourd, Tennessee Sweet Potato, and White Cushaw.
C. maxima: Banana, Boston Marrow, Buttercup, Delicious (all types), Essex Hybrid, French Turban, Hubbard (all types), Mammoth, Mammoth Chili, Marblehead, and Olive.
Pumpkins and squashes do not cross-pollinate with cucumbers, watermelons or citron. Watermelons and citron both belong to the same genus Citullus and, therefore, will cross-pollinate each other. Muskmelons and Casaba melons will cross since they are both in the same genus Cucumis and also in the same species melo.
Here's a tip on how to get non-cross-pollinated seed:
You can plant squash of the same species and save seeds too. Check your blossoms the night before and pick a male and female that should open the next morning. Take a bit of masking tape and tape the blossom ends shut. The next morning, pick your male flower and untape. Untape your female and hand pollinate it. Tape it back shut, and mark that blossom with a bit of yarn or something.
Squash produce so many seeds, that you can do 2 or 3 flowers and have tons of seed for growing, trading or selling. Then let everything grow and pollinate as they naturally do. When harvest time comes, you have your marked squash to save seeds from. Once a flower is pollinated (and not subject to pollen carried on the wind), you could also put it in a little net bag; just don't use the drawstring as it can be hard to remove. Use a twist-tie or a bit of cotton around the stem.
Cucurbit flowers open shortly after sunrise and remain open until late afternoon or early evening. Accordingly, each flower is open for only a few hours. The honeybee is the most common and effective pollinator of cucurbits. Honeybee activity closely coincides with the period when the flower is open. Honeybee visitation begins an hour or two after sunrise and continues until midafternoon. If temperatures are very warm, bee activity may decline about noon. Research on cantaloupe pollination conducted in California showed that bee visitations increased until 10 a.m. and then declined until 3 p.m. when activity almost ceased.