Biennial bearing in pears , apples and other fruit trees

Not every crop is Biennial. Some fruit trees are predispositioned to this condition. Biennial bearing - Wikipedia
" Biennial bearing (or alternate) bearing is a term used in pomology to refer to trees that have an irregular crop load from year to year. In the “on” year too much fruit is set, leading to small fruit size. Excess weight in the main branches can be too much for their mechanical resistance, causing them to break. Another major consequence is that flower induction will be lower, and the subsequent year will be “off” year (too little fruit).

The behavior could be due to plant hormones, particularly gibberellins produced in excess in the “on” years in the embryos of the young fruit. It could also be caused by depletion of carbohydrate reserves in the tree.

Biennial bearing is more common in certain fruit crops like mango, apple, pear, apricot and avocado, and is almost nonexistent in grapes.

Biennial bearing is a regular feature of Arabica coffee production in Ethiopia and East Africa, and indeed throughout the coffee-growing world. In Biennial bearing a good or excellent (bumper) crop is followed by a poor, low-yielding crop in the next year’s harvest. This phenomenon occurs independently of weather and climate, so that even when climatic conditions are favourable for a good crop, the yield can be poor. There can be a fivehold (x5) difference between on and off years, although in extreme cases there can be a tenfold (x10) difference in Ethiopia and areas of East Africa.

The biennial cropping rhythm is due to the allocation of the plant’s resources: in the productive ‘on’ year, the coffee tree puts it’s resources into producing the crop at the expense of vegetative growth (stem growth and particularly shoot development and flower bud production); in the ‘off’ year the plant must make up for this vegetative shortfall, at the expense of flower and fruit production.

Biennial bearing can be reduced or almost eliminated using various means, including pruning, the addition of fertiliser, controlled irrigation and the use of selected vigorous clones or cultivars."

"Why do fruit trees tend to bear heavy fruit crops every other year?


Why do fruit trees tend to bear heavy fruit crops every other year?


The tendency of fruit trees to bear fruit in two-year cycles, consisting of a large crop followed by a small crop, is termed alternate or biennial bearing. Alternate bearing occurs in almost all tree fruits.

The flowers that produce next year’s crop are initiated during the development of the current season’s crop. When a fruit tree is producing a large fruit crop, most of the tree’s energy is utilized for fruit development, little energy remains for flower initiation. As a result, a fruit tree often produces a small number of flowers and fruits when preceded by a heavy crop the previous year.

To discourage alternate bearing, home gardeners should thin apple and other fruit trees when fruit set is heavy. Hand thinning of apples should be done within 6 weeks of full bloom. Leave the largest apple in a cluster unless it is damaged. After thinning, apples should be spaced about 8 to 10 inches apart on the branches. Pears, apricots and peaches may also need to be thinned. Fruit should be spaced 6 to 8 inches apart on the branches. Plums will generally thin themselves. " Why do fruit trees tend to bear heavy fruit crops every other year? | Horticulture and Home Pest News

Now that we understand the problem and some solutions it will be easier to prevent Biennial bearing | Good Fruit Grower

Biennial bearing

Growth regulators can tame a common bad habit.

April 1st 2011 Issue

Richard Lehnert // April 1, 2011

Developing seeds inside apples send strong signals to apple shoots telling them not to set flower buds for the next year. Thinning reduces this signal.

Developing seeds inside apples send strong signals to apple shoots telling them not to set flower buds for the next year. Thinning reduces this signal.

Photo courtesy of Steven McArtney

Biennial bearers are the bane of apple growers, but the industry is growing more of them. Many newer varieties, like Honeycrisp, Pacific Rose, Fuji, Cameo, and Braeburn, are prone to alternate light and heavy cropping.

Biennial bearing can have a pronounced negative economic effect on orchard productivity and fruit quality, says Dr. Steven McArtney, southeast apple specialist at North Carolina State University. Cumulative yields are lower, and fruit on light-cropping trees often develops calcium-related storage disorders like bitter pit.

Even the less-prone varieties can be shocked into biennial bearing patterns by such events as major freezes that eliminate apples for a year. “Frost damage is a tremendous trigger for biennial bearing,” he said.

McArtney has made a career of searching for ways to settle biennial-tending varieties into annual bearing patterns. He’s been the apple specialist for the four southeastern states of North and South Carolina, Georgia, and Tennessee since 2003, after spending 16 years with HortResearch in New Zealand.

He described Pacific Rose as “the beast that got me started. This is a great apple to eat, but a terrible variety to grow because of biennial bearing. When I was at Hort­Research in New Zealand, Pacific Rose was referred to by many in the industry as ‘Pacific dog’ because of its severe biennial bearing tendency.”

A successful chemical thinning program will often result in returning an orchard to consistent cropping, he said, noting that after chemical thinners came to the market about 1950, the national apple crop showed much less year-to-year size fluctuation.

Studies show that the seeds in developing apples produce gibberellins that suppress bloom the following year by inhibiting flower bud formation. Lots of fruit mean lots of seeds, and that means few flowers the following year.

“Chemical thinners take off a lot of fruit—and also a lot of seeds,” McArtney said. “Thinning takes away the gibberellin signal. Without the signal, you’ll more likely get a flower.”

But with the really sensitive varieties, like Honeycrisp, Pacific Rose, and Fuji, a good chemical thinning job is not enough to guarantee a good return bloom, he said.

The following are the steps apple growers might want to try if they’re hoping to tame a problem orchard’s ­biennial bearing.

Thinning: Do a good job of chemical thinning using combinations of products like Sevin (carbaryl), NAA (naphthalene­acetic acid), and MaxCel (6-benzyladenine).

Summer sprays: Use NAA or Ethrel (ethephon) summer sprays in the heavy cropping year to increase flower bud formation the next year.

NAA may be applied in four applications of 5 parts per million two weeks apart in June and July, or it may be applied in four weekly sprays starting one month before harvest. The preharvest spray somehow changes vegetative buds to flower buds, even after the usual period when the tree makes these decisions, McArtney said.

If Ethrel is used, it should be applied once six weeks after bloom. The rate of Ethrel depends upon the variety, he said. Severely biennial varieties like Fuji might need rates as high as 72 ounces per acre, while varieties that are only slightly biennial will only need 16 ounces per acre. A rate of 48 ounces per acre is recommended for Golden Delicious. Ethrel should not be used on Honeycrisp as it might worsen preharvest drop.

McArtney finds NAA easier to use in the orchard because it is one rate for all varieties and can be included with summer cover sprays.

Bud analysis: Dissect some buds after harvest and see how many are vegetative and how many will throw blooms next spring. What you find will help you decide how heavily to prune next winter. When cut open, the meristem appears either flat or domed—and the domes are the first sign of next year’s flower buds.

“If your orchard is a mixture of heavy- and light-­cropping trees within a block, then you might want to delay pruning until you can see what you’ve got,” he said. “Don’t bother pruning the light-­flowering trees, and prune the heavy-flowering trees more aggressively.”

Hand thinning: Follow up with hand thinning where necessary, setting a target number of fruit per tree and taking off the smallest fruit, and paying no attention to fruit spacing.

McArtney spoke to growers on this topic during the Mid-Atlantic Fruit and Vegetable Convention in Hershey, Pennsylvania, last winter."


Certainly a investing topic given the posts the last few days. I never would have thought there was chemicals that could help with this. Anyone know if the chemicals are included in the soil or on the tree itself and if they are available to the general public?

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1-Naphthaleneacetic acid ( NAA) is easy to find this ebay vendor has been selling it for years

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Since the seeds produce a hormone which reduces bud formation it would follow that cultivars which tend to have reduced seed formation in the fruit should be more often likely to bear regularly. ‘Centennial’ crab comes to mind. It’s productive every year with low seed set. A fair number of the fruits turn out to be seedless even.


What happens when a tree has been grafted with multiple varieties? If one of the varieties is strongly biennial, will the entire tree become biennial?



No not at all multigraft trees don’t change the way a pear produces completely. It’s my opinion if you graft a quick to produce pear on the tree the others should produce faster due to hormones but the bad news is the pears don’t share my opinion. I’m still trying combinations and some with success but from the rootstock not other scions.

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There is much more to trees than biennial fruit production and I’m not at all sure we understand what is going on yet. Honeycrisp might take off several years or it could produce every year. Some claim their thinning skills were the key to success.

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Many of my plums have gone biennial a year after producing heavily, without thinning. That’s logical. They spent so much energy one year, they need to rest and recover the year after.

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Yes my experience is the same some plums went biennial but others didn’t. Some pears do the same. What’s confusing to me are sometimes I might go years without a crop like the case of honeycrisp. Honeycrisp produce heavy every year for 5 years and then take 4 years off. Very confusing not every treetops that. Pears in general lean towards biennial tendencies.

My 13 years old Honey Crisp took about 6 years to fruit. Then, it went biennial. After that, when I thinned thin well, it cropped the next year ( decent crop). When I did not thinned well, it skipped a year. It has never skipped more than one year.

Last year, it had very light crop. This year it is full crop. I wonder if you thin your apples much :grin:. I see your pear trees. I don’t think you thin them much, not at the level I do.

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No I don’t normally thin fruit typically. My plums, peaches, and cherries are not biennial. My pear trees were not all grafted at once so if they are biennial it’s OK. Definately doesn’t matter if you have enough pears. If 50 pears produce this year and 50 pears produce next year that’s the same as if I remove half the pears on 100 trees both years. Why do the extra work with no gain? Except pears produce a partial crop on their off year. By not thinning I get more fruit. There are exceptions some pears might be grown for size in which case it matters. Ayers as an example it does not matter at all. Apples don’t produce well here ever. They are not biennial. Haralson is a consistently good producer it’s the exception. All other apples are unpredictable for me. Most home growers thin because they have 2 or 3 trees so they get a crop every year. Many times the weather thins for me. What good does it do to remove half your crop to have a freeze the following year? I’m only pointing out my reasons for what I do not persuading others to use a method not applicable to their situation. Kansas is a marginal climate so i get what I can get while I can get it normally. There are always exceptions. My honeycrisp are very old as well on mm111.

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Well Bud formation is governed by Cytokinins, not Auxins. Cytokins do not travel down the limb so limbs should not effect bud formation of other branches. I guese.

Eh apples produce so much it does not really matter if thinned in my experience. I live in the Applewood portion of Golden CO. Our neighborhood used to be a apple orchard so nearly every home has a apple tree here. I have read dwarf apple trees need staking and that a lot overbear fruit and go biannual. Our neighbors have a dwarf tree that produces apples without stakes. Our apple trees produce so many apples every year. Every year many in this neighborhood don’t harvest them as well which I see as wasteful but that is beside the point of course. There is a path we walk on by our house and while not reachable there is a pear tree is someone’s back yard. I did not see any pears on it in previous years which to me suggests it too young in previous years prior to last year to bear. Last year I saw many pears develop on that tree. This year I saw many flowers on it but we had a late frost. You want my opinion on trees that have a hard time at least in Colorado it is stone fruit and certain kinds. Pears, apples and plums do super well here and there are articles from our local extension telling us they do well here. Cherries and peaches often get nipped off the tree by a early frost here. I am a die hard cherry fan and cherries last along time so will likely not get rid of my cherries. My peaches on the other hand that only live for 20 something years on the high side without getting heavily diseased I am thinking of taking out. The weather will basically ensure about half the time they are alive I will not get peaches.



Try Reliance or contender peaches they both do well for me. I prefer Reliance but contender is later which extends the season. Golden is a nice town its one of several places in Colorado I like. The water is very pure there.

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I have one pear tree with about eight different limbs/varieties. The limbs of Harrow Sweet and Korean Giant fruit each year while the others don’t. I was also hoping that the slow to fruit varieties would be influenced but it hasn’t happened.

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Bud dormancy , fruiting and other things are hormone driven in pears as your aware
The government is interested in this very much Melatonin Induces Parthenocarpy by Regulating Genes in Gibberellin Pathways of ‘Starkrimson’ Pear (Pyrus communis L.) - PMC
There are others who had the same ideas we had
Diffusible and extractable auxins in young Japanese pear trees - ScienceDirect

You will now know why the formula of sevin dust was changed because there are many people who thinned using sevin Can You Sterilize A Tree - How To Keep Trees From Fruiting

Disease also is influenced by hormones Fire Blight | WSU Tree Fruit | Washington State University

Different trees are impacted differently by hormone and disease

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@clarkinks … great information. Personally, I really dislike the Idea of using chemical thinners but I understand the need in commercial orchards. We have several small orchard blocks on our property consisting of apples, apricots, cherries, nectarines, peaches, plums and pears. Hand thinning is a big job in 80+ trees. I totally ignore the pears and cherries except for the thinning influence of pruning. Nectarines and peaches are thinned to increase size and reduce load stress on branches. Crop setting for them seems most influenced by weather. Thinning apples trees to avoid biennial bearing is indeed time sensitive. I work on the most egregious offenders… er overproducers first. Wolf River, Northern Spy, Lodi, September Wonder, Yellow Delicious, Honey Crisp and Gold Rush. I never seem to complete this task in a timely manner. Maybe I need to host a Thinning Party!!! :partying_face:
The Mount Royal plum overproduces every year and has to be thinned for flavor. Anyone else have this problem?
I have decided to just enjoy my orchard and the variables of production. Perfection is not worth the stress.



Sometimes people fight what we need to learn to live with eg. Biennial fruit production. That’s been the case for me many times I try to fight nature before I realize nature was right all along. There are many people who realize to late something doesn’t work in their area. They are out there spraying their pears but that’s a perfect chance to let nature do its job thinning. PC are crushed by pears growing so what harm will they do? I’m not suggesting we never need to act I’m suggesting sometimes we overreact as orchardist. Sometimes we need to thin so branches are not broken on a few trees.

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Perennial fruit trees that were bred with production in mind require significant input of a broad base of nutrients each year for production the next. Without them, the plant will self-regulate and conserve resources.

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