Assure Good Blueberry Pollination to Get the Most Out of Your Blueberry Bushes
Achieving good blueberry pollination is one of the keys to getting a great blueberry crop. Blueberry bushes that have been pollinated properly will yield larger berries, and a larger percentage of blueberry blossoms will set fruit.
What does that mean to you as a blueberry grower?
Well, there are some things that you can do to assure that your blueberries are indeed well pollinated.
In fact, you can help assure that your blueberries will be well pollinated before you’ve even planted a single bush.
The Mechanics of Plant Pollination
As you may know, the plants of most flowers have both male and female parts. The male part is called the stamen, and it produces the pollen. The female part is called the pistil, and it must receive the pollen in order to achieve fertilization, which results in the ‘birth’ of a plant embryo (seed).
But since plants are unable to transfer pollen from the stamen to the pistil, they need some help. That’s where honey bees and other pollinating insects come in.
The flowers bribe insects with nectar and with the pollen itself, which is an extremely protein-rich food source.
When an insect visits a flower to collect some of the free pollen or nectar, they unintentionally transfer some grains of pollen from the male parts to the female parts. In true symbiotic fashion, both the plant and the insect help to ensure the survival of their species through the exchange of payment for services (inadvertently) rendered.
It’s a win-win not only for the insect and the plant, but also for the countless other creatures – including us – that depend upon the life-sustaining food that the pollinated plant will produce.
Some plants are pollinated by wind or by animals such as bats instead of, or in addition to insects.
Blueberry Cross-Pollination: Be Picky About the Varieties You Choose
Each pollinated blueberry blossom produces one blueberry. And like the fruits and seeds of most plants, the size and quality of that blueberry will be dependent upon how well the blossom was pollinated.
For many plants, the best pollination is achieved when pollen from the male parts of one plant is transferred to the female parts of a different plant of the same species, rather than just within the same blossom. This is called cross-pollination.
Most blueberry varieties are self-fertile. This means that as long as blueberry pollination occurs within a flower (or among flowers of the same variety), that flower will set fruit and produce a blueberry. But blueberries happen to be among the set of plants that benefit from cross-pollination.
For most blueberry varieties, blueberry pollination will be more complete when a blossom is cross-pollinated with another variety. This means that more seeds will be formed as a result of the blueberry pollination, resulting in a larger berry.
How to Choose Blueberry Varieties for Cross-Pollination
When you’re selecting blueberry varieties for your garden, trying to assure that you’re picking varieties that will cross-pollinate each other can be a bit ‘headachy.’
There are so many different varieties of blueberries within each species (rabbiteye, highbush, etc.) to choose from. And there’s no ‘master chart’ of blueberry pollination – that I’m aware of, anyway – that lists every possible variety of every species and shows what other varieties are compatible as cross-pollinators.
So how do you know which varieties to choose for cross-pollination?
The best way is to buy your plants from an established, reputable nursery, whether local or online. They should be able to recommend cross-pollinating varieties (online catalogs often list blueberry pollination recommendations in the variety’s description).
If you can’t get a specific recommendation, then compare the chill hours requirement of the varieties you’re considering for cross-pollination. The chilling hours requirement is simply the amount of cold a fruiting plant must be exposed to before it will break winter dormancy.
So let’s say you’re considering two varieties for mutual cross-pollination. Variety A has a chill hours requirement of 800 hours, and variety B has a requirement of 600 hours. The two varieties aren’t ideal cross-pollinators because variety B will likely begin to bloom considerably ahead of variety A.
On the other hand, if A required 800 hours, and B required 750, then that’s pretty close, and odds are good that the two varieties will be good cross-pollinators. (The chilling hours requirement can also be a good indicator of whether a plant will do well in your area.)
Also remember that plants can only pollinate other plants of the same species.
Rabbiteye blueberries won’t pollinate lowbush, and lowbush won’t pollinate highbush, etc. So if you happen to live in a borderline area where you can grow two different species, just keep in mind that each species will need pollinators of the same species.
Planting For Optimum Pollination
Getting the best results from cross-pollination involve more than just selecting the right varieties. It’s also important that the cross-pollinating plants be close enough to each other, and that there not be too many of one variety and too few of another.
For blueberry pollination, the spacing isn’t really super-critical for cross-pollination purposes. But you do want to have the cross-pollinating varieties reasonably close together.
For example, if you have a variety on one side of the yard, and a pollinating variety over on the other side of the yard, the blueberry pollination results may not be the best.
If the plants are widely separated, then bees will be less likely to visit both varieties in one foraging trip. And that means poor cross-pollination.
Quite often, one particular variety is the most desired variety, and other varieties are grown mainly to provide pollination for the favored variety. When this is the case, there’s likely to be considerably more of the ‘star’ variety than the ‘supporting cast’ varieties.
That’s OK as long as things don’t to get too out of balance.
I don’t know of any university recommendations for cross-pollinator ratios. So I’ll just tell you that based upon my own experience, I’d prefer not to exceed a ratio of around 3 to 1. For every 3 plants of the ‘star’ variety, I’d have at least one of the pollinating varieties.
Insects for Blueberry Pollination
If you’re a home gardener, it’s unlikely that you’ll be renting hives of honey bees to pollinate your few blueberry plants, as commercial blueberry growers do.
So in a way, the information provided here about blueberry pollinating insects is just an interesting side note. But it might be fun to watch your blueberry plants while they’re in bloom just to see which insects are working the hardest at helping you produce a great crop of blueberries.
There are a number of insects that are minor blueberry pollinators, and those vary some from region to region. But in general, the two primary blueberry pollinators are bumblebees (a catchall term that refers to a number of Bombus species) and honey bees.
Bumblebees are the more effective of the two at blueberry pollination. Their tongues are long enough to reach through the long, narrow blueberry blossom to the base where the nectar is secreted. Honey bees have shorter tongues, and have more difficulty reaching the nectar.
Bumblebees also use a unique method of collecting pollen, called ‘sonication,’ which makes it a more effective pollinator.
When a bumblebee collects pollen from a blossom, it will hang upside down on the flower, with the opening of the flower positioned over the bees’ belly. It then vibrates its flight muscles, dislodging grains of pollen that fall from the flower onto the bees’ belly. The bee then brushes the pollen grains from its belly into the pollen baskets on its hind legs.
If you gently hold a twig between your fingers that’s attached to a blossom that a bumblebee is sonicating, you’ll easily be able to feel the vibrations of the bee at work. It’ll feel as if the twig is buzzing in your fingers.
Sonication is extremely effective at pollinating a self-fertile flower, but it’s not effective for cross-pollinating. Bumblebees cross-pollinate as they go from flower to flower gathering nectar.
Honey Bees Do Their Share…
If you just compare a single bumblebee to a single honey bee to decide which is the most effective at blueberry pollination, the bumblebee would win the contest hands down.
But honey bees hold one singular advantage over bumblebees that makes them the #1 pollinator of commercially grown blueberries – numbers. A single hive of honey bees can number in the tens of thousands in population.
So while a single honey bee can’t do the pollinating work of a bumblebee, hundreds or even thousands of honey bees certainly can.
That’s why many commercial blueberry growers pay beekeepers to temporarily scatter hives of honey bees throughout their blueberry orchards. It’s worth the expense, because the busy guest workers can significantly increase the quantity and quality of the harvest.
Hey, That’s Cheating!
Another type of bee that can often be found buzzing amongst the blueberry blossoms is called the carpenter bee.
Carpenter bees are small, and have no hope of reaching through the open end of the blossom to the nectar at the base of the flower. Their tongues simply aren’t long enough to reach that tantalizing pool of nectar at the bottom of the blossom.
But that doesn’t mean that the carpenter bees are left out; they still manage to snag their share of the sugary treasure. They take a shortcut by snipping out a small incision at the base of the flower. It’s then an easy reach for them through the hole and right to the nectar.
That solves the problem as far as the carpenter bee is concerned, but it creates a problem for you, the blueberry grower.
That’s because the carpenter bees’ shortcut allows it to completely bypass the pollen-bearing parts of the flower. So as the carpenter bees gather nectar, they do no pollinating at all. They sort of cheat the blueberry plant, you might say – treasure taken without services rendered.
But what’s worse is that honey bees that come along later and visit the same blossom will take advantage of the carpenter bees’ shortcut and slurp nectar through the hole – again without doing a bit of pollinating.
So if an area has a high population of carpenter bees, the effectiveness of honey bees as blueberry pollinators is diminished. (Interestingly, bumblebees just ignore the carpenter bees’ shortcuts, and always probe for nectar from the top of the flower. No cheating for the bumblebee!).
Fortunately, though, not all honey bees take advantage of the carpenter bees’ shortcut.
I’ve spent many hours watching the bees at work in our blueberry orchard. (I guess you could say I’m easily entertained!). And I’ve noticed that some honey bees ALWAYS use the carpenter bee hole, and some honey bees ALWAYS probe for nectar from the top, whether the blossom has a carpenter bee hole in it or not.
So carpenter bees don’t eliminate the effectiveness of honey bees as blueberry pollinators, they just diminish it somewhat.
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