If you've ever planted a saved seed and grown a fruit or vegetable that looks nothing like the one the seed came from, what you've grown is called a hybrid. The flower on the original plant was fertilized by a different species through a process called cross-pollination.
What Is Cross Pollination?
Cross-pollination occurs when pollen from one flower reaches the pistils of another flower. This plant therefore "pollinated" another plant, and the genetic material will combine. When seeds of this plant are saved and regrown, a hybrid is produced.
Your hybrid plant is probably an accident of nature, but intentionally crossing species to create plants with tastier fruit, bigger blooms, different colors, and other desirable characteristics is a big part of gardening culture.
For the home grower, understanding cross-pollination helps you plan a garden that's going to stay consistent with your intent.
What Is Cross-Pollination?
Understanding cross-pollination helps to know how plants reproduce through flower, fruit, and seed development. Flowers can be complete, which means they have both male and female parts, or they can be incomplete with only the male (stamen) or female (pistil) parts.
For plants with incomplete flowers, fertilization occurs when insects or wind carry pollen from the stamen of a male flower to the pistil of a female flower. The pollen is captured at the top of the pistil (the stigma) and drops down to fertilize the ovule, which develops into a fruit or a seed.
The mixing of different characteristics occurs during seed development, and all flowering and cone-producing plants can cross-pollinate by natural or mechanical methods. This happens with plants in the same genus with some more vulnerable than others. It is rare for plants in different genera to cross-pollinate.
Certain fruits and vegetables are more vulnerable to cross-pollination, which makes saving seeds a wasted effort. Others with seeds as the edible portion, like sweet corn, can cross-pollinate to produce a variety entirely different than what you planted.
Some plants produce both incomplete male and female flowers on a single plant, and these are types likely to cross-pollinate. A honeybee visits a male flower on a zucchini plant, picking up grains of pollen from the stamen. Then, she flies off to the female flower of a butternut squash growing nearby. Once there, zucchini pollen falls off her body onto the butternut flower stigma. The resulting fruit will still be butternut squash, but the seeds inside it develop combined characteristics of both zucchini and butternut squash to produce a cross or hybrid.
Sweet corn is an example of how cross-pollination can alter the ear, which is the part we eat. If you plant a sweet yellow variety next to a sweet white variety, there's a good possibility both crops will produce mixed ears. Sweet corn also cross-pollinates with field corn, resulting in a tough, chewy vegetable and a ruined crop.
Trees and Shrubs
Many fruit trees and shrubs that produce berries require two plants of the same type or a second plant of a different species to form fruit, since many fruit plants are unable to self-pollinate. Two plants increase the chance for fruit with more flowers maturing at different times.
For example, holly shrubs develop only male or female flowers pollinated by bees. Two are needed, one male and one female, for the female shrub to produce berries. Pawpaws have complete flowers but the female (stigma) matures before the male (stamen) produces pollen. By the time pollen is available, the stigma is no longer receptive or able to use for fertilization.
Explaining Self-Pollination vs. Cross-Pollination
Self-pollinating plants produce complete flowers with both male and female parts in each bloom. Cross-pollination is still possible, but less likely because both reproductive parts are available in all the flowers on the plant and in close proximity.
Self-pollinating vegetables include beans, broccoli, cabbage, carrots, cauliflower, corn, kohlrabi, onions, and peppers.
If you've saved seed from an heirloom tomato you plan to grow again next year, it's a good idea to isolate it from other varieties by 25 feet. Odds are in your favor that the fruit will remain true to the parent, but a possibility exists you've saved the one seed visited by a bee carrying pollen from a different variety.
How Hybrids Form from Cross-Pollination
A hybrid plant has a combination of characteristics from different parent plants in the same species. These plants are created through cross-pollination by insects, environmental factors, and by humans. Plant experts also use other methods to develop hybrids and the quest to grow a marketable cultivar with desirable characteristics is competitive. It takes effort and many years of trial and error to achieve market-worthy status. Meyer lemons, Better Boy tomatoes, tangelos, and jostaberries are examples of commercially viable hybrids.
Garden edibles grown from packaged hybrid seed often have better disease resistance. But saved seed can be sterile and. when viable, is more likely to grow less vigorously that the parent plant. Resulting fruit is variable with smaller blossoms and yield. Check your seed package for the symbol F1, the word 'hybrid', or its abbreviation 'hyb.' Plant purchased seed, instead of saving your own, to guarantee dependable results.
Saving Seed for Next Year, South Dakota Extension