Many old shrubs can be rejuvenated by cutting back some - or all - of the mature growth. It can either be carried out in one hit, or more sensibly in stages.
Most will know that 3 in 1 oil works wonders for getting things moving again. For getting shrubs moving again, let's reverse the numbers and think 1 in 3. One in three is a basic shrub pruning technique that really does wonders for a wide range of shrubs - mainly deciduous but also with a few evergreens that can benefit from selective shoot pruning. Basically, you select one stem or branch in every three and cut it back near to ground level at the base of the shrub.
This method is normally used to rejuvenate shrubs from the base upwards. But with slight modification, it can also be used further up the shrub on lateral or spreading branches.
Many shrubs - especially if grown in close proximity to others in a bed or border - will eventually become top heavy with growth and flowers on the uppermost branches of the shrub. Main reason being that shrubs need light to grow, and if crowded will do what they do best - reach for the light on long stems that are mainly lacking in foliage or flower power.
Most shrubs flower on relatively young growth or twigs that are normally 12 months old. They rarely flower on older branches. Most of the newer branches are at the top of the shrub, where the active growth has been going on.
The end result being a high canopy of flowers and foliage, each year getting further away from the all important root system, and as a result, smaller blooms or flower trusses are accompanied with ever weakening foliage.
Flowers and foliage of shrubs such as Roses and Buddleias are normally bright, large and healthy because they are cut back hard each spring. A neglected Buddleia or Rose will soon start sending out smaller flowers as the shrub's growing tips get further away from the food source.
Roses and Buddleias can be cut back hard each year because they flower on growth that is made in the same season. If you were to cut back a forsythia in the same manner, it would be 2 years before flowering well. This is because they would fistly have to grow a framework of support branches in year 1, then in year 2 they would grow flowering twigs or spurs on that support system. So cut back hard spring 2015; grow support framework throughout summer 2015; grow flowering twigs and spurs through summer of 2016; flower at last in spring 2017!
Remember! We are talking only of Rejuvenation Pruning of older shrubs. Normal pruning takes precedence with younger shrubs.
This method will have to be adjusted according to how the basal framework of individual shrubs it set at ground level. Some shrubs will have a single main stem from which the framework branches grow. Other will have many ground level stems that sucker up from the root system. Most shrubs which are more than 4 years old will have a good selection of branches from which to choose your 1 in 3 for the chop!
By cutting out one in three as in the image which conveniently has 9 main stems (crafty), you will be leaving two thirds of the shrub to grow as normal and carry on producing flowers the following year. The stems that are not pruned out will benefit from the lack of immediate competition, and will develop well and probably produce as much or more flower than if no action had been take.
The stems that have been cut back, will soon start to grow new framework branches for they are now near to the food source and in any event benefit from the added vigour of the branches which have not be cut.
The following year, you can then cut out further stems from the old original framework, for you will now have a mass of newer stems from the year 1 cut back!
Year three should see the remainder of the old stems cut out, so you then end up with a shrub which has a bushier habit, with better looking newer foliage, and continuation of flowers.
This activity will not necessarily reduce the height of the shrub, for it will still have the root system that wants to replace all the cut off growth back to its original size.
There are many others that have strong basal framework growth.
The best time for Remedial Pruning, is immediately after flowering certainly within a month of flowering ceasing.