The Art and Science of Pruning 
Everyone loves to prune. And at the beginning of each new season, we’re all chomping at the bit, itching to get started. In fact, this time of year I get more questions about pruning than almost anything else. However, there's more to pruning than just going out and cutting off branches or vines. There is an art and a science to pruning - and they go together. 

Pruning is both a dwarfing and invigorating activity for the plant. It helps you manage tree size and shape, while maintaining a proper level of growth to ensure healthy, annual bearing. You prune to get rid of last year’s unwanted growth, dead or diseased limbs, open up the tree and restructure the canopy for better light and air penetration, encouraging good fruit bud formation, and quality fruit development. Pruning too early can lead to bad results under the wrong circumstances – since you may prune off more potential fruit, lose crop to a freeze or frost, and send the plant back in to a vegetative phase. Prune too little and the crop suffers. Pruning too late can just as easily cause an imbalance and poor fruit quality by eliminating too much of last year’s reserves from this year’s growth and fruit. 

Why Prune?
Pruning is fundamentally about maintaining a healthy functional plant architecture, including maintaining a proper fruit to vegetative bud ratio, fruiting branches between 2-6 years old, and an open canopy. You need to prune your trees in a manner that ensures proper limb spacing, orientation, age, and size. Too many bigger, older limbs and you end up with trees that quickly decline in terms of the productive potential. Too many smaller, younger limbs and you end up with a tree that doesn’t have enough bearing wood and low productivity. Small, weak, damaged, rotten branches will never function properly, nor will they provide the structural strength needed to carry a crop.

The ideal is a good mix of young and old, big and small, properly spaced and oriented to permit good sunlight penetration, air movement, bearing and non-bearing wood for solid annual productivity.  A healthy, physiologically active tree is the goal – and an annual pruning program will ensure this. Even if, you are shooting for distressed trees in order to drive down the vigor and drive up the concentration of fruit qualities, you need to prune. Low-functioning and diseased trees will not produce fruit of any quality except poor. And by the same token being heavy-handed with the loppers will lead to trees being over-vigorous and susceptible to all kinds of insect and disease issues - not to mention out-of-sync fruiting cycles. Pruning is an art and science. If you understand the science, but use your creative side to apply it, then you may end up with an orchard that outlives you. Pruning, as in all things in life, is about balance. And balance is the secret to happiness, no matter whether it is your trees or you - hopefully both. 

Pruning - Cause and Effect
•    Sunlight – first and foremost plants need quality sunlight. Without light they can’t photosynthesize, support a crop, develop high quality fruit, or develop fruit buds for next year. Opening up the tree or vine with proper pruning so the sunlight can reach all areas, striking the leaves and bark optimally is critical. More than anything else we do in farming, we principally are in the business of harvesting sunlight. Adequate pruning is critical for semi-dwarf and larger trees. It was shown years ago that even in well-pruned semi-standard trees, only about 30% of the canopy (the exterior 30%) gets enough sunlight. The rest is shaded to varying degrees. So simply consider this: sunlight = sugar. If you’re not photosynthesizing, you’re not growing. The sugars produced during photosynthesis help the developing fruit buds overwinter properly and grow strong next spring. 

Suffice it to say that before we can harvest any fruit, we first have to harvest the sunlight.

•    Air Movement – second only to sunlight, you need to consider how air moves through your tree's canopy and the crop, and how pruning can help that process. Good air movement in concert with good sunlight penetration can help dry out plants after a rain or heavy dew, while helping moderate the temperature throughout the tree. If your trees can't breathe, they suffocate.

•    Water and Nutrients. Pruning also helps manage the number of growing points in the plant. Each growing point requires a certain amount of resources to grow properly. Too many growing points and it dilutes the available resources to other part so the plants. Too few and the plant could grow excessively vigorous, even rank, growth with very few fruit. So before you start pruning always keep in mind the ratio of fruit to vegetative buds on the plant before making the first cut. The rule of thumb for apples is that you need 20 leaves per fruit to grow healthy fruit. You can also calculate the number of apples per tree based on trunk cross sectional area (TCSA). For grapes, the number of buds you leave behind determines the number of potential fruiting clusters. Of course, in both cases the vigorousness of the tree or vine should also be used to fine-tune your pruning approach. 

o    If you need to remove a large number of growing points, do so with a few cuts. This is ALWAYS better than making a lot of little cuts. The more individual cuts, the stronger the tree reacts, and the more adverse the reaction.

•    Housekeeping – winter pruning is also a good time to remove old and diseased limbs. In fact, this is where I usually start because it gets the obvious cuts out of the way. Limbs typically produce quality fruit well for the first two to six year, maybe up to ten. But as they get older, their ability to produce quality fruit and well as their propensity for diseases suggests that maintaining fruiting wood at an average of less than 10 years old will encourage a long-productive life for the tree. All damaged wood, especially diseased wood, should be pruned out and removed from the orchard.

Pruning is about architecture, sunlight, air movement, resource allocation, and housekeeping, all in the support for healthy trees and annual fruiting. 

Pruning for Fruit and Productivity
Of course, pruning is fun and can help you develop an aesthetically beautiful plant. But the vast majority of people also want to get some fruit off of those trees every year. Return bloom is a tricky thing to manage in apples – especially in varieties that have a tendency to bear every other year. But the only things we know are what we know, so we need a good head for conjecture. That said, I hate to leave things to chance. After return bloom, cold damage to fruit buds, either from frost or cold winter temperatures, is the most likely time that we’ll see major unavoidable changes to our crop potential. That’s why I like to wait as long as possible to prune. 

Yet, the biggest regulator of the plant’s growth response is your crop, the one you haven’t seen yet. That’s why predicting the unknown is a critical skill. There are ways to assess potential crop load before we start to prune to give us a baseline. 

•    Shape and size
•    Microscopic Analysis
•    Forcing buds
•    Varietal tendencies
•    Last year’s crop
•    Winter Temperatures
•    History

Generally speaking, though, we won’t know what our crop is until it is actually on the tree or vine.

How do I develop a pruning strategy for Bearing Trees?
Developing a pruning strategy starts by asking questions and making some estimates of return bloom. You can start by understanding the basic growth and fruiting tendencies of the your particular variety and rootstock combination .
 
•    How old are my trees?
•    What is general fruiting to vegetative wood ratio?
•    Is your orchard on a strong site – in other words, do the trees naturally grow more vigorously there than on another site?
•    Do you have early or late blooming varieties? 
•    Consider the cold hardiness of your particular varieties, rootstocks and locations; factor in the potential for spring frost using your site history 
•    Did I have a crop last year?
•    How big was my crop last year? 
•    What do the buds “look like” on the tree?
•    What if any cold damage past, present or future have the trees experienced? 
•    Do I have a “frosty” site
•    Finally, while the basic principles of pruning are the same no matter what size trees you have, you will want to adjust your pruning style based on tree size and crop objectives. Some additional questions to ask – What size fruit do I want? Does this variety return bloom well? Is my fruit intended for fresh market or cider? 

Once you answer the above questions, you have what you need to develop a sound pruning strategy. The point of this – and it does have some bearing on crop load management – is to determine how much and when you really want to start pruning. There is no harm in waiting to prune, unless you wait too long . Pruning late can be a good risk management strategy, but waiting too long can reduce resource allocation from the winter reserves to remaining buds. However, by waiting you can better assess the return bloom, crop load potential, and get past the coldest part of the winter. Waiting no later than tight cluster to prune has been shown to have no impact on tree or fruit quality. 

Pruning too early doesn’t give you the option of backing off or adjusting your pruning to accommodate any winter damage, frost potential, or low return bloom. If the unforeseen occurs, there are always ways to adjust for unfortunate circumstances. For now, start as late as possible and make sure you leave enough time to get your pruning done by tight cluster. If you can wait, then wait. 

Rehabilitating Old Apple Trees
Renovating and rehabilitating old apple trees and orchards differs from planting a new orchard. First, and this is really important, you have make sure the trees are alive. There’s no point in trying to revive a dead tree. Depending on how far gone the tree is, you’re sometimes better off turning the tree into firewood. But if the tree is still alive [or a good portion of it at least], then you need make a careful assessment of quality of the trunk, bark, scaffolds, dead vs living branching, how dense the canopy is, etc. to determine what approach you take. Decide how aggressive you want to be, perhaps staging the pruning over a few years rather than doing it all at once. Also, depending on the health of the tree, you will want to assess the quality of fruit buds, if any, and whether to prune for a crop or not. But mostly this workshop is about taking trees that are in various stages of decline and bringing them back to life.  

WHERE TO START REHABILITATING YOUR OLD APPLE TREES. 
1.    The first year you’ll want to make large cuts rather than do a lot of fine pruning. 
2.    Remove all dead wood and branches. 
3.    Open up canopy by removing
a.    large branches and creating windows for sunlight
b.    branches that are dense or matted together. 
c.    Pendant branches
d.    Vigorous upright branches
4.    Clear up around the base of the tree. This will stimulate nutrient release, biology and improve soil aeration and water penetration – all working to help the tree grow and thrive.

Good luck out there and have some fun!