This was kindly sent to us from Stephen Phillips, The Vice President of Bainbridge Island Fruit Club. I am anxious to try it out.
Some people are intimidated by pruning. The expert advice can be confusing so I put this together and hope it helps.
I have links below to some really excellent resources on pruning fruit trees. If you know of others, let me know and I’ll try to add them to the list. As to the confusing or conflicting part- Growing conditions and weather are a part, goals and resources of commercial and backyard orchardists differ, and cultural differences between pomme and stone fruit, as well as differing vigor of various root stocks affect growth habits. Finally young trees are handled differently than old trees. A few basic principles may be helpful in understanding the experts advice. I am commenting here on healthy apples in the maritime northwest.. Radically pruning mature or badly diseased trees is a special case for another time.
Periodic pruning is a necessary activity, not an option. Each cut will influence the future development of the tree. Its shape, production and vigor, the quantity and size of fruit. Trees which are not pruned will produce smaller and lower quality fruit.
-Branches which don’t get sunlight won’t produce much or any fruit. Thinning the upper branches helps get light down to the lower ones.
-Generally speaking vertical branches will produce leaves but not much fruit, horizontal branches will produce the most fruit, and drooping branches are not as good as gently rising ones. UC Davis suggests a 45 degree angle for branches coming off of the trunk.
How the tree grows-
-Auxin (Indole Acetic Acid ) is a chemical produced by the terminal bud of a branch. It causes the branch to elongate, and make side buds. It seems that high concentrations of IAA inhibit the growth of the side budson the stem. Pruning the the end bud on a branch eliminates the source of auxin. The side lateral shoot, just below it is no longer inhibited, and starts producing its own auxin. It becomes the dominant bud and that is the direction the branch will start growing . Terminal cuts farther away from a lateral will tend to promote lateral growth over several buds going down the stem . Authors differ on how far down the branch this continues. Somewhere between 8 and 16 inches Keep this in mind when you are choosing where to prune.
When to prune:
When you prune will also have implications. Diseased and structurally unsound wood should be taken out whenever you notice it. Cutting it out controls disease spread, and directs nutrition airflow and sunlight to the remaining branches. Very narrow crotches will generally become a problem, and they should be removed before they split. When you do the other pruning will depend on your priorities. Advocates of winter pruning note that it is easier to see the branches when the tree is dormant and many of us have more time in the winter. Summer pruners say it is more enjoyable and faster to do it in the summer while you are thinning the fruit. The effect on the tree is different as well.
Winter pruning tends to promote a vigerous flush of new growth the following spring. These water sprouts produce leaves, not fruit and should be removed.
Summer pruning limits the growth of the tree and minimizes water sprouting- The spring growth spurt has come and gone, and reducing the leaf canopy in the summer limits the amount of nutrition available to be stored which controls growth. This dwarfing effect diminishes as the summer progresses. There is also research suggesting that early summer pruning can increase flower bud set. Since the flower buds set this year will become flowers the next year, this may be a help with apple varieties which tend toward biennial fruiting. It seems that this pruning should be done within 8 weeks of bloom.
What to cut off?
Although the trend in eastern Washington orchards commercial orchards is to use a V type which looks almost like an espaliered hedge from a distance, our area seems to favor more traditional tree shapes either the central leader or the open vase systems.
Here are some links :
Simplified pictures, descriptions of the systems: http://www.groworganic.com/organic-gardening/articles/pruning-fruit-trees-choose-training-shapes-for-apple-peach-cherry-trees
How much to take off? Orchardists with grown trees tell me that taking off about 20% of the new growth in our area is about right with apples. Stone fruit with their more vigorous growth and different laterals, should have about 50% taken off.
UC Davis excellent overview of pruning fruit trees:
Hope this helps
Other interesting somewhat related links:
A very old and comprehensive discussion of grafting techniques
Electron microscopy of flower/pollen and fruit set http://fruitandnuteducation.ucdavis.edu/files/162093.pdf
Good photos of different stages of flower development