In the fruit garden no work is so rewarding as summer pruning. A little effort spent on this task pays you back in so many ways and it is really rather essential for properly maintaining any trained forms of fruit. Summer pruning checks growth and done correctly leads to better quality fruit more reliably, and with less work and wasted plant material. Winter pruning is done while the plant is out of leaf and has different effects; promoting growth and is more useful when forming a tree or re-invigorating it than for the maintenance of good quality crops.
In summer we are cutting out soft shoots and unripened growths and these are easier on us and our tools than the harder ripened shoots of winter. And by taking them sooner we don't leave them to grow using up the plant's resources only to be cut off in winter and burnt or shredded. The smaller bits removed in summer are full of sap and can be added to the compost and soon rot down.
The check to the plant of losing a lot of leaf area, soft wood and many buds redirects the growth to maturing and ripening fruits, and to forming more flower buds rather than growth buds on the wood left. This gives more flower and fruit the following year rather than more wood. It is this check from removing material while the sap is flowing that makes it so different to winter pruning which encourages rather than checks growth.
The opening up of the plant in the middle of summer by removing a great bulk of the shoots and leaves lets air and light penetrate and pass much more freely. This improves the quality and sweetness of the fruits plus they now also receive a larger share of nutrients from the roots. Cutting away much of the total leaf area also reduces the demand for water during dry weather further benefiting the fruit. All of these effects further benefit the remaining wood left by helping it to ripen. So wood and buds much lower down mature ready to burst next year whereas if left unpruned till winter it would be those nearer the top that would have matured and then only to be removed. Thus summer pruning creates the densely spurred stocky growth we are after rather than long lanky unfruitful growth.
However although the leaf area is itself very significantly reduced by summer pruning the total amount of light captured and converted to sugars may remain much the same as it now falls on once shaded leaves more fully exposed. (Much the same argument applies to pests that attack leaves such as gooseberry sawfly and redcurrant blistering aphids -if the leaves are destroyed it lets the light fall on other leaves that were previously shaded thus up to a certain level of damage many pests and diseases could be considered as doing the summer pruning for us. In particular sweet cherries are prone to black aphis attacks which generally wither the tips and end leaves -any damage on this scale increases the flower buds providing yet more cherries for the blackbirds to steal.)
Much of the benefit is also in controlling the size of the plant. Trained forms such as cordons, espaliers and so on need pruning to maintain their chosen form. If these are only winter pruned they will tend to put on too much growth and be full of unproductive wood. Summer pruning not only keeps them producing crops instead but keeps their shape and appearance near constant. (Bush and relatively untrained forms can equally benefit but are just harder to get at and keep in order.) Obviously the leaders, the shoots being left to extend the framework, must be left untouched in most cases though with grapes these too need shortening. Shoots going in the wrong direction such as towards the wall for a trained form are best cut out entirely. Otherwise all shoots are shortened, depending on the subject and it's vigour, by about half their own length more or less. The more vigorous the harder they need to be cut back. (Short shoots that have stopped extending and end in a fat fruit bud, brindles, can be left if you recognise them.)
Summer pruning is best commenced about midsummer, with the soft fruit before the top. Redcurrants and gooseberries first and grapes which need more than any other subject and are really a specialist case. On most specimens I reckon it is best to start with the top growths on the first pass as growth rushes to the top and if you cut the bottom first this only reinforces it. By trimming back the top third of shoots the bottom two thirds grow stronger. Then on the second pass a week or two later the middle third gets cut back further promoting the lowest growths. Finally on the third pass the lowest are trimmed and by this time they have usually formed some good strong growths. It is generally difficult to get lower branches or shoots to extend because of the dominance of the higher growths but by pruning down in this way any shoot can usually be increased sufficiently and fruiting retained over the whole framework. (For greatly increased extension of any shoot do not bend down and tie it until it has reached the desired length but allow it to grow as near vertically as possible.)
Ideally summer pruning is done in these several stages so as not to unduly shock the plant too much, and preferably with sharp, sterilised with alcohol, secateurs or knife. Now although it all sounds very technical and complicated and rather crucial to get it right do not be too concerned. I have heard of many successful growers who summer prune with shears or even hedge trimmers! After all if you think about it; a regularly and properly maintained cordon is pretty close to being sparsely covered topiary. And all other trained forms are just assemblies of cordon trained branches.
We want to remove all the outer growths retaining the form and the minimum of wood, preferably covered with stubby spurs full of fruit buds in as tight a cylinder about each branch and stem as possible. So there is much to be said for using shears to do a quick job on the first couple of passes and then a refined tidying job on the third ensuring that only the very best placed wood and buds are retained for ripening through the autumn. Anyway if you leave too much it can still be trimmed back further in winter -though as stated this is not so good and wastes the trees resources.
In fact although we are discussing summer pruning something akin to it is done even earlier in the year, from when growth starts, for rather than leave shoots in the wrong places to grow at all they are best rubbed off before they have even finished leaving their buds. Other shoots in better places can be nipped to stop them extending as soon as they have grown long enough. This sort of continuous rubbing out and nipping in can produce the most amazing results but to be fair does require an inordinate amount of attention.
And of course there are the exceptions; some plants must be treated differently. Raspberries, blackberries and the other related hybrids that form multi-stemmed stools are best allowed to form long canes. Though these could be summer pruned if you bizarrely wished to form (short-lived) branched frameworks out of them. These much more benefit from having their new small or congested canes thinned out entirely and all their old ones removed straight after fruiting. Blackcurrants are similar only having one third of the whole stool cutting back each year. (At the time you pick the fruit, if you want the currants to stay fresh leave them on the branch and keep it in water, and if you give fruit to friends this saves your picking it!) Treat the blackcurrant stool like a pie and cut a third slice off each year removing all those shoots down to the ground.
Several of the stone fruits are similar to blackcurrants needing their young shoots to be retained and disposing of the older. Morello cherries, nectarines and peaches are thus either best left almost entirely alone or pruned on what is called the renewal or replenishment method. This is almost the same for other tip bearing fruits such as most of our early season apples which are difficult to prune any other way without removing too much of the fruiting wood. For all these you need to retain the whole length of the best young shoots and to remove as much as possible of the older wood without removing too much young wood along with it! A tall order! Continuous cutting out of the old immediately after fruiting and replacing them with the strongest new shoots from as far down the growth as possible is the ideal. All unwanted and congested shoots are trimmed back very hard, only leaving a couple of buds to produce more replenishment growths for the next round.
Grapevines require as much attention as you can give them but respond magnificently. They are so prone to making luxuriant growth when given a free root run that seriously vicious summer pruning is required to coerce them into ripening their fruit properly and early enough! And unlike the others these are much more prone to making long sideshoots as soon as you stop the main ones, and sideshoots on sideshoots. I first stop all shoots except any leaders about a half dozen leaves after the flower truss. On the second round all surplus shoots are cut back hard except those deemed to have good set trusses of berries. On the third all sideshoots are stopped and any leaders as well. It also helps to get earlier crops if you do the winter prune as soon as possible, even before the leaves fall. And grapes also need heavy fruit thinning as well -with about half the bunches removing from most vines, and if you are really keen removing half the berries from the remaining half!
Fruit thinning as well as summer pruning is certainly advantageous for most fruits, especially the larger ones; peaches, apples and pears which may swell significantly to gourmet proportions. The redirection of resources plus the reduction of numbers not only gives us even better quality fruits but also reduces the stress on the plant. It is the number of seeds that exhaust the plant not the number or weight of fruit pulp surrounding them. Thus the thinning then makes for more reliable regular cropping. Fruit thinning is probably most sensibly done in three passes; one immediately after each pruning.
It's a very good policy to collect all summer prunings up and compost or deeply bury them along with any fruit thinnings. This eliminates a lot of pest and disease organisms rather than leaving them to survive on the ground. And after pruning and thinning it also makes sense to remove any suckers and weeds from around the base and to give a good watering to help the plants recover.
As said at the beginning; with trained fruits of almost all sorts you really can vastly improve the quality of your crop and control the plants size very effectively by such simple means. Thus it is a skill we all should practice on our prized crops. Even so I know some who never summer prune their gooseberries any more simply because they reckon it's ten times more painful than winter pruning!