Summer pruning

Winter pruning vs. Summer pruning

The main  objective of Winter pruning is to develop and maintain a strong, well balanced, branch structure. 
This is achieved by establishing  dominant leaders  (through  apical dominance ) with lateral branches that are no larger than half the leader diameter.  
Winter pruning generally promotes vigorous new  growth , while  Summer pruning retards growth -  the new growth tends to  be much less vigorous.
Pruning in Summer thus saves the  tree from wasting energy when the unwanted new, vigorous, Winter pruning growth is later removed.
Summer  pruning  can control size  and  the shape of  fruit  trees, and - by  increasing the movement of air through the canopy - help to control diseases.
Summer pruning also helps to maintain the  critical balance between  new vegetative growth and fruitfulness.

Pruning cuts

There are two basic pruning cuts :
Heading cuts are where terminal stems and  branches are cut back.
Heading cuts remove the dominant apical growing tip and this releases the side buds to grow resulting in an unwanted, more dense, vigorous growth at the point of pruning. Heading cuts  result in a thicker and denser canopy that will reduce light levels within the tree.  Apical  dominance then  has to be re-established by  thinning-out the  dense new  growths to establish a new dominant leader.

Thinning cuts remove stems or branches at their point of attachment.  This results in much less vigorous  regrowth  (due to the retainment of apical  dominance) and improved light penetration.
When making  thinning cuts  prune just outside the branch collar - this will lead to rapid wound closure and the prevention of decay in the main stem or branch. 

When  Summer pruning use mainly  thinning cuts (rather than  heading  cuts)  and prune to an outward  facing  bud.

Summer  Pruning

Summer  bearing fruit trees are best pruned as soon as possible after the fruit has been harvested 
( providing the weather is not  wet). 
Summer pruning wounds heal rapidly  -   less chance of diseases entering through open wounds  (important for apricot  and cherry  trees).
Summer prune for sunlight  -  open up congested canopies and allow  light into  the trees, this will help keep  flower buds alive for next  year's  fruit crops. 
Cut out completely all in-growing branches to open up the  centre  of the tree.
Prune  crossing over branches  and cut out all dead or diseased (gumming ) wood.
Much of the new growth made since spring can be cut back by at least half.

Once a system of summer pruning is established, very little winter pruning  is  required  and a better balance  between vegetative  growth , flower development and fruit production  is maintained.