We all learn about pollinators from childhood, but a deeper dive into growing plants might introduce us to another term: pollenizer (sometimes spelled polliniser, polliniser, or pollinizer). The two sound similar enough to be often confused, but what do they really mean?
A pollenizer is a plant that is a source of pollen. Broadly that can mean all flowering plants, but gardeners are most likely to come across the word in the context of growing fruit cultivars, many of which need pollen from one of a specific list of other cultivars in order to set fruit. A pollinator, on the other hand, is an insect, bird, or other creature that transfers pollen from one plant to another. Abiotic (non-living) agents of pollination, like wind and water, are sometimes also referred to as “pollinators.”
Examples of Plants and their Pollenizers
| Plant | Pollenizer |
| Apples* | *Some apples, called triploids, need two different pollenizers that are not also triploids |
| most commercially grown apples (malus domestica) | other apple cultivars; crabapples |
| Blueberries | |
| highbush blueberries (Vaccinium corymbosum) | other highbush blueberries |
| lowbush blueberries (Vaccinium angustifolium) | other lowbush blueberries |
| halfhigh hybrid blueberries | other halfhigh hybrid blueberries; highbush blueberries |
| Rabbiteye blueberries (Vaccinium ashei) | other rabbiteye blueberries |
| Cherries | |
| Sweet cherries (Prunus avium) | any other sweet cherry |
| Sour cherries (Prunus cerasus) | any other sour cherry |
| other cherry species | cultivars within their own species |
| Grapes | |
| Muscadines (Vitis rotundifolia) | Other muscadine cultivars, especially the few self-fertile ones such as “Carlos” and “Noble” |
| Haskaps, aka Honeyberries | |
| all Haskaps (Lonicera caerulea) | any unrelated haskap variety |
| Pears (Pyrus communis)* | *some pears, called triploids, require two different pollenizers |
| European pears (Pyrus communis) | most other European pears; Seckel is the least flexible |
| Asian pears (Pyrus pyrifolia) | specific Asian pears; of the European pears, occasionally Bartlett |
| Plums | |
| European plums (Prunus domestica) | any other European plum; some American plums |
| Japanese plums (Prunus salicina) | any other Japanese plum; some American plums |
| American plums (Prunus nigra and Prunus Americana) | any other American plum |
Why Are Pollenizers Needed?
In nature, some flowering plants reduce or prevent their seed production if they’re pollinated with their own pollen. This is called “self-incompatibility” and it’s an effective way to ensure genetic diversity throughout the generations. As a result, they must have a source of pollen from another plant of the same species: a pollenizer.
In agriculture, many plants we depend on are actually clones. Each gala apple is genetically identical to every other gala apple. Without cloning we would not be able to fill stores around the world with a steady supply of named fruits with recognizable shapes and flavours. Imagine planting a seed from a golden delicious, tending it for years, and finally discovering that its fruit—which has a new combination of genetics from its male and female parents—looks and tastes different from what your market expects.
Cloning avoids that problem, but if you fill an orchard with golden delicious trees, you have, genetically, filled it with a single tree that cannot self-pollinate. Some cultivars even have sterile pollen. The solution? You fill about 10% of your orchard with a pollenizer, like a crabapple or another marketable cultivar that is genetically similar enough to fertilize your crop, but not so similar that it triggers self-incompatibility. Bees (your pollinator in this example) transfer the pollen from those trees to your golden delicious blossoms, allowing them to turn into fruit. Note that the genetic makeup of your pollenizer won’t affect this generation of apples; however, it would affect the next generation if you tried to plant their seeds.
If that’s hard to wrap your head around, think of it this way: the fruit is not the plant’s offspring; it is an organ the plant uses to grow their offspring, their seed. Just like the tissues in a mammal mother’s womb are controlled by her genes, the tissues in the fruit are controlled by the plant-mother’s genes. The only place the plant-father’s genes end up is inside the seed.
That’s an oversimplification, but I hope it helps with a concept that is often hard to grasp.
As with the flowers we discussed at the beginning of this section, your fruit trees are receiving pollen from a plant in the same species, just from a different cultivar or variety within it.
How to Pick the best Pollenizer for Your Crop
To be useful, a pollenizer must produce a good quantity of fertile pollen. It must not be so genetically similar that self-incompatibility is triggered (at least for species where self-incompatibility is an issue), and its flowers must be open at the same time as those on your primary crop. Here’s an example from my own garden: Squash can be self-fertile, but they often produce many male blossoms before their first female blossom—and those blooms last for just one day. If I care more about having lots of fruits than about collecting pure seed, I’ll grow a few varieties together to maximize the time during which I have male and female blossoms flowering simultaneously. In this case, all of the squash plants end up acting as pollenizers for one another.
Squash are easy because they can all fertilize each other, and they bloom for long periods of time. With fruit trees and shrubs, on the other hand, there is a much smaller window for blossom time, so specialized knowledge is needed. The catalogue of a fruit-tree nursery in your region is likely a great place to find information about which plants require specific pollenizers. When I ordered apple trees from Whiffletree in Ontario, for example, their catalogue told me which of their cultivars to combine for the best results. Of the options they presented, I narrowed it down based on which ones were suited to my climate and soil conditions.
Another method nurseries use to simplify matters is to categorize cultivars into “Group 1,” “Group 2,” and “Group 3,” depending on how early or late they flower. Buyers can simply choose multiple varieties from within the same group.
Some plant breeders have developed cultivars that are specifically meant to be grown as pollenizers rather than for the fruit they themselves produce—for example, seedy watermelons that only exist to provide pollen for sterile seedless varieties.
For commercial producers, there are extra factors to consider when choosing one or more pollenizers. If 10% of an orchard is to be given to pollenizers, do they choose a variety that is very fertile but isn’t worth harvesting, like crabapples? If they choose one that is marketable, will it make harvest more complicated to keep it separate from the main crop? Is there a market that will accept that smaller volume of fruits? Do the two cultivars have the same requirements in terms of fertility and pest management?
A piece of advice that is useful for truly maximizing a harvest is to select two pollenizers: one that will begin to bloom just before your chosen cultivar does, and another that will finish blooming just after it. This will make sure your plant’s full blossom time is covered, although it does reduce the amount of space you can dedicate to your primary cultivar. Some cultivars of pear and apple actually require two different pollenizers to get the job done; they are called triploids, in contrast to single-pollenizer-requiring diploids.
How To Space Pollenizers Among Your Primary Crop
Depending on circumstances, commercial growers might plant between 10% and 50% of their field or orchard with pollenizers. But it isn’t enough for the pollenizer to be present; for the pollen to be shared effectively, those plants must be distributed evenly amongst the others. The most efficient way to design a layout for pollen distribution is to imagine the field as a grid, with the corner or side of every main-crop square touching the corner or side of a pollenizer square. However, some growers find it more cost effective to prioritize harvest efficiency, so they plant their pollenizers in straight rows.
According to the University of Georgia’s Honeybee Program [https://bees.caes.uga.edu/bees-beekeeping-pollination/pollination/pollination-crop-pollination-requirements.html], some growers get around the problem of losing orchard space to pollenizers in innovative ways. They graft crabapple branches onto their main-crop apple trees, or bring in barrels of cut crabapple branches when the trees are in bloom. The same post shares very specific advice about how to consider bees’ preferences in your orchard and is well worth a read for anyone setting out to grow fruit on a large scale.
I have spent the most time talking about fruit trees in this post, because their needs are complicated, but remember that you are using pollenizers every time you grow flowering plants of the same species together and allow cross-pollination to occur. There is a good deal of specialized knowledge related to pollenizers, but the word itself—although it’s often met with confusion—represents the simple idea of a plant that gives pollen. Since word choice tends to be a source of confusion in this area, here is a quick reference guide for related vocabulary:
Self-fertile vs. Semi-fertile
A self-fertile plant does not need pollen from another plant to produce fruit. On the other hand, a semi-fertile plant is capable of setting some amount of fruit when pollinated with its own pollen, but it tends to produce lower yields. Having a pollenizer present will improve the production of a semi-fertile plant.
Self-fertilization
Self-fertilization is a process of pollination in which a plant is fertilized by its own pollen. This can take place between male and female flowers on that plant, or within a flower that has both male and female parts. The process is usually facilitated by a living pollinator or by the wind or, rarely, water, but a few plant species have mechanisms that allow them to self-pollinate without help.
Pollenize
“Pollenize” and “Pollinize” are both acceptable American spellings, and “Pollenise” and “Pollinise” are both acceptable British spellings. The word is unfortunately a synonym for “pollinate,” which can be confusing since, as we have established, “pollenizer” is not a synonym for “pollinator.” The word likely came into English through the French: “Il pollinise.”
Monoecious
A monoecious plant produces both male and female flowers. If it does not have a mechanism for self-incompatibility, and if its male and female flowers are open at the same time, it’s likely to not require a pollenizer.
Self-incompatibility
This mechanism ensures genetic diversity within a plant population by inhibiting seed production if a plant is pollinated with its own pollen.
Dioecious
A dioecious plant produces only female flowers on some plants and only male flowers on others.
Androecious
An androecious plant grows only male, pollen-producing flowers.
Gynoecious
A gynoecious plant grows only female, seed-producing flowers.
Bisexual Flowers
Also called “perfect” flowers, these contain both male and female parts to produce both pollen and seed. Some cultivars with bisexual flowers are not self-fertile and still need a pollenizer.
Finally, just to reiterate:
Pollenizer
“Pollenizer” and “Pollinizer” are both acceptable American spellings, and “Polleniser” and “Polliniser” are both acceptable British spellings. The word refers to a plant that is a source of pollen.
Pollinator
A pollinator is a living being that transfers pollen from one plant to another. The word is also occasionally applied to non-living agents that transfer pollen, like wind or water.
Bibliography
Honey Bee Program. “Crop Pollination Requirements.” University of Georgia https://bees.caes.uga.edu/bees-beekeeping-pollination/pollination/pollination-crop-pollination-requirements.html
Schultheis, Jonathan R. (2007). “Planting Pollenizers Strategy for Watermelon Production.” Growing Produce.
Meeuse, Bastiaan J.D. (2021) “Mechanisms that prevent self-pollination.” Encyclopaedia Britannica. https://www.britannica.com/science/pollination/Mechanisms-that-prevent-self-pollination
“How does this pollination stuff work anyway?” Fedco Seeds. https://www.fedcoseeds.com/trees/pollination.htm
Hodgson, Larry. (2021). “Fruit Trees: it usually takes two.” Laidback Gardener. https://laidbackgardener.blog/2021/02/27/fruit-trees-it-often-takes-two/
Grant, Amy. (2021) “Grapevine Pollinating Needs: are Grapes self-fruitful” https://www.gardeningknowhow.com/edible/fruits/grapes/grapevine-pollination-needs.htm
Dray, Delia and Campbell, Jill. (2007). “Crabapples as pollinators.” NSW Government Department of Primary Industries. https://www.dpi.nsw.gov.au/agriculture/horticulture/pomes/apples/crabapple-pollinators
“Pollination—Pear” Washington State University Comprehensive Tree Fruit Site. http://treefruit.wsu.edu/web-article/pear-pollination/