For the sake of this HowTo we are talking about pruning in the context of making large changes, reshaping or curing problems such as disease.
When to prune plants is one of the most common questions for gardeners and if you ask 20 people you will likely get 20 answers as to when the best time for pruning is…
The truth be told the best time to prune is when the job needs to be done and when the weather is not so inclement as to harm the bush or tree you are working on.
For instance you wouldn’t want to prune your bushes or trees in the middle of the summer when your area is going through a heat wave and in the same sense if you are sitting in your home in the middle of winter with nothing to do, going outside in an ice storm is probably not the best time to do it either.
If you find that your trees or bushes are in distress you should not wait to take care of the problem.
If you go through a storm and one tree damages another or a higher branch falls on a lower limb or bush you should not only clear away any debris but you should also prune to eliminate future inset of disease.
General Garden Management
If you are pruning your garden plants for aesthetic reasons or to manage their continued growth and not for immediate need then pruning of any plant should be performed during its dormant season.
For most regions of the country this means in the fall after leaves have fallen or in the spring before they have started to grow.
There are only a few exceptions to this rule and that would be for trees that flower early in the spring. If you find a need to prune your flowering trees in the spring then you should wait until after they are done flowering.
For the exact times you should consult a local arborist that can give you details for your area and plant type.
When in doubt always prune when the tree or bush is dormant.
Or as said above prune any plant when its health is in concern.