North American Fruit Explorers mailing list at ibiblio

[Alan Haigh <alandhaigh@gmail.com>]

Of course, biennial bearing is related to a wide range of factors.  Just as a cool wet spring can prevent flowers from setting fruit, inadequate days of full sun and periods of cool can stop a tree from manufacturing adequate carbohydrate to invest in flower bud formation for the following year. 

 

The longer fruit hangs on the tree the more of an investment is required in carbohydrate whether we're talking tiny surplus apples (which need to be thinned by about 2 weeks after petal fall) or the harvest itself.  Even the level of brix that an apple develops is directly related to how much energy was required for its formation.  High brix apples tend to have more biennial issues just as late ripening ones do.  Fuji and Goldrush are both extremely high brix and very late.

 

Imagine how much more energy an apple tree in the West can harvest with the nearly rainless, cloudless growing season, except on the coast, than those of us in more humid parts of the country.  Imagine how much more light can be harvested from a tree growing in the open.  On hot days the stomates close and carbo production is brought till a standstill after mid-morning until early evening- especially on apples.

 

Thinning fruit is helpful but not a panacea, no matter how timely.  Pruning a tree in an open form so each branch gets the maximum amount of sun also helps.  Anything that augments a trees ability to harvest light near where the fruit is or will form next year including some summer pruning may help.

 

On the Bramley in question the fact that it is on seedling rootstock may actually be quite helpful.  I manage a lot of huge apple trees of varieties that are notorious for biennial bearing and I believe that vigorous root stocks are less prone to this problem if managed properly.

 

I usually gradually remove much of the highest wood to create a low spreading tree where no large branches block the light of any other.  I kind of create a single plane branch structure that has plenty of room.  As the old timers used to say- "needs to be open enough that you can throw a cat through it".

 

I mop out the water sprouts in mid- summer on the more vigorous trees so the light and sap goes where it's needed.