Pollination Myths

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Gardening myths abound, and we’ve probably all been guilty of perpetuating some of them until we learned better. Although much of garden mythology is benign, misconceptions about pollination can be downright serious, affecting the types of plants we choose to grow or the quality of seeds that we save. With that in mind, it’s prudent to dispel some popular myths about pollination in home gardens once and for all.

Myth 1: Sweet peppers and hot peppers need to be separated in the garden, or you’ll be surprised with hot sweet peppers.

It is true that most varieties of hot and sweet peppers grown in home gardens are the same species, Capsicum annum, and capable of cross-pollinating, but that is the only grain of truth to this common pollination myth. Cross-pollination of almost any fruit or vegetable variety will only affect the NEXT generation of plants grown from the seeds. That means that you won’t know that cross-pollination has occurred until you save seeds from those peppers and grow them out the following year. Why does it only affect the next generation? The flesh of a pepper, like other fruits, doesn’t develop from the fertilized ovules — it develops from the ovary wall that surrounds them. This means that the genetics of the mother plant determine the characteristics of the fruit that is produced, not the genetics of the seed.

Basic flower anatomy (adapted from Wikimedia Commons).

Basic flower anatomy (adapted from Wikimedia Commons).

 

What about the pepper seeds, you ask… shouldn’t they be hot? Capsaicin, the substance which gives peppers their heat, is not produced in the seeds at all, but is abundant in the inner membrane and fleshy interior ribs that support them.

So, basic botany explains how this myth is biologically implausible, but how much should you trust theory? Three summers ago, a friend asked me to start 6 seeds for him of Bhut Jolokia, or “Ghost Pepper” — the hottest pepper in the world at the time. Chris let me keep one of the plants, which I planted in the garden right alongside my other sweet and hot peppers. The Bhut Jolokia was one of the most prolific peppers we grew that year, spreading taller and wider than any of the other plants (over 5 ft high) and producing loads of scary-red peppers. I harvested the Ghost Peppers with gloves and a doubled ziplock bag, but we never tasted any additional heat in any of the other 18 varieties of peppers that I grew that year, including the sweet peppers grown immediately nearby.

 

Myth 2: Cucumbers and squash should never be planted next to cantaloupes or honeydews, or they will cross-pollinate and you’ll end up with bland-tasting melons.

Although cucumbers, squash, muskmelons, and watermelons are all cucurbits, they are all different species, making it genetically improbable for them to cross-pollinate, with some rare exceptions (primarily among winter squash species). Varieties within the same species can cross-pollinate (e.g., cucumbers with cucumbers), but even then, like peppers, you won’t know it until you grow out the seed the next year. When a melon doesn’t match your expectations for taste, environmental factors are most likely to blame (melons are very sensitive to water and soil fertility), not the 20 zucchini plants in your neighbor’s backyard.

Is there ever a time that cross-pollination matters to the harvest? It does if you are growing corn. Sweet corn grown next to field corn will be starchy and tough, as the genetics of the pollen contribute to the character of the developing kernels (~30%). Why is corn an exception? Basic botany comes to the rescue again. The proper development of corn kernels, like the seeds of other flowering plants including pepper and melons, requires double fertilization — that is, two sperm (carried in the pollen) are required to fertilize an ovule. One of the sperm fertilizes the egg within the ovule, which becomes the plant embryo. The other sperm fuses with other nuclei in the ovule to become the endosperm of the seed, which will develop into a food source for the developing plant. The endosperm makes up the majority of a corn kernel, which is why the genetics of the pollen source matter so much. In contrast, there is very little endosperm in the seeds of other garden plants, which instead put all of their resources into developing the cotyledons (seed leaves).

 

Myth 3: Tomatoes are self-pollinating, so no special isolation steps are necessary for saving seeds for replanting next year.

There are some elements of truth in this myth. Tomatoes are self-fertile, but they aren’t self-pollinating in the truest sense of the word. If this doesn’t make sense to you, take a closer look at a tomato flower. You won’t find pollen on exterior anthers; instead, the pollen is produced internally and must travel down a hollow stamen and drop onto the stigma. Left on their own, tomatoes don’t set fruit well — motion is required to shake the pollen out. Wind can do it, but bees do it most effectively, which is why greenhouse-grown tomatoes will fail to set fruit unless bees are introduced (or humans agitate the plants). Hurray for pollinators!

Although most of the pollen that reaches the stigma of tomato flowers is from the same plant (similar to peppers), there is still the opportunity for cross-pollination. If you grow several varieties of tomatoes in your garden each year and you want to make sure that your seed is pure for saving, simply exclude the pollinators using caging around the plants, or bags around the flowers. Most seed-savers don’t take such steps, however, as the frequency of cross-pollination is pretty low (1-5%). And if the number of tomato offerings in the Seed Saver’s Exchange Yearbook is any indication, most folks prefer variation in tomatoes anyway.

 

Myth 4: Since bean flowers self-pollinate before they open, the seeds will always breed true for seed-saving.

Most beans do in fact self-pollinate before they open, and for many varieties of beans cross-pollination is indeed a rare occurrence.  Hungry bumblebees can facilitate crossing when they chew through unopened bean flowers to gain access to the nectar, as heirloom bean expert Bill Best explains in his book, “Saving Seeds, Preserving Taste.”

Many varieties of beans, although self-pollinating to a large degree, still require visits from pollinators to set the maximum number of seeds. Lima beans in particular perform better with the services of pollinators, as unlike most bean species, the anther and stigma do not contact one another during flower development. Instead, most of the pollen falls onto the style (which supports the stigma); when a bee pushes it’s head into the flower, the style and stigma are forced out, the style’s pollen is dusted on the petals, and the stigma picks some of it up when it retracts. Although wind may also help lima bean pollen find the stigma, bees more effectively “trip” the flowers and get the pollen where it belongs (or deliver pollen from other bean plants in the process). From my own experience in the garden, I can attest that we saw a major difference in fullness of our lima bean pods after we began beekeeping and attracting native pollinators.

 

Myth 5: Honeybees are the most important pollinators to the home gardener.

Honeybees are invaluable workers in the home garden, but as much as we love our hives, I would argue that we exalt them at the expense of our native pollinators. If you love to grow squash, bumblebees are far more important. Cowpeas? Invite wasps, a misunderstood garden ally (as explained here). And don’t forget about the thousands of species of native pollinators, such as mason bees, sweat bees, leafcutter bees, and carpenter bees (I see more of these native bees working in my garden than my honeybees, who live in hives placed right at the garden’s edge). Many folks wouldn’t dream of swatting and killing a honeybee, but yet consider these other important pollinators a nuisance. Let’s look out for all of our pollinators, o’kay?

Bumblebees doing all the work pollinating squash blossoms.

Bumblebees doing all the work pollinating squash blossoms.

 

9 Comments

  1. terrirochenski

    June 21, 2013 at 7:51 am

    Excellent post! Thanks for all the great explanations.

  2. Peter Kuhns

    July 8, 2013 at 8:08 pm

    Phew! Good to see I’m not crazy (or lying). Anyway, great article.

    • Ma Hubbard

      July 8, 2013 at 8:17 pm

      Thank you!

  3. Melissa (AKA Bee Girl)

    March 5, 2014 at 8:12 am

    Great facts here! Thank you for setting the record straight!

  4. Andrea

    March 7, 2014 at 12:46 pm

    Very interesting! Number one I had always heard the other way…that if you want heat in your hot peppers, don’t put them next to sweet peppers, because they will be bland. Should we still separate the pepper plants if we plan to save the seed, since the cross pollination will show up in the next generation?

    • Ma Hubbard

      March 7, 2014 at 8:58 pm

      Very interesting, Andrea. Yes, if you are seed-saving, make sure that cultivars are separated.

  5. April Harshbarger

    May 13, 2014 at 8:40 am

    Thanks so much for this article. I was wondering why I sometimes end up with weird yellow striped zucchinis, but I’m glad to know I don’t need to try to separate the squashes from each other. Plant biology is so amazing. You could learn about it for years and still find new things.

    • Ma Hubbard

      May 14, 2014 at 6:00 am

      I think plants are pretty amazing, too, April. Thank you for visiting!

  6. KC Tomato

    September 22, 2014 at 10:29 pm

    Tomatoes, especially those with fasciated fruits, have been documented to outcross at much higher rates than indicated here. Richardson (TGRC 3:1953) reported rates of 10-17%. That is high if one is trying to seed save and maintain a variety.