Late summer or early fall pruning causes vigorous regrowth, which in some cases may not harden off by winter, leading to possible cold damage. Whenever unexpected damage from vandalism or bad weather occurs, prune at once.
http://www.savvygardener.com/Features/pruning_shrubs.htm
most spring blooming shrubs require pruning after the blooms are gone, but before fall.
It is recommended to trim bridal wreath shrubs after they have finished blooming in the spring. This allows you to shape the shrub and encourage new growth without cutting off potential flower buds for next year. Avoid trimming the shrub in the fall or winter to prevent removing the buds that will bloom in the spring.
There are a few ways to trim round shrubs. If you want a formal look, use an electric trimmer. This will create straight edges. If you want your shrubs to look more textured, you should use clippers to open up space into the plant.
Trees and shrubs can be lightly pruned anytime in Florida. To minimize reduction of next year's flowers, prune spring-flowering plants such as azaleas, in late spring before the flower buds set for the next season.
To ensure that you trim shrubs evenly, use a measuring tool like a string or a level to guide your cuts and maintain a consistent height. Step back periodically to check for symmetry and adjust as needed.
Yes, you can trim your bushes in October in Kentucky, but it's important to consider the type of bushes you have. For deciduous shrubs, late fall can be a suitable time for pruning, as it allows you to shape them before the winter dormancy. However, avoid trimming spring-flowering shrubs, as this could remove buds for next year's blooms. Always ensure to check specific care guidelines for your particular plants.
Trim in in the spring before the leaves come out.
Early spring. You can trim up to 1/3 of the stalks, and trim from the ground up.
This is a very comprehensive answer from NC State University: http://www.ces.ncsu.edu/depts/hort/consumer/factsheets/shrubs/text/pruning.html
Shrubs that do not have blooming flowers need to be trimmed just when the weather is starting to warm up after winter. A person that lives in a climate that does not have snow can trim their shrubs whenever they need it.
Generally, it's towards the end of winter that you trim, prune or otherwise cut shrubs in Pennsylvania. But that decision depends upon two conditions. One condition is the particular pruning schedule of a particular shrub. For example, early spring blooming shrubs generally need their care delayed until after the bloom.Another condition is the reason behind the care. Care may be done any time that the reason may be said to begin with the letter 'D'. Specifically, that means if the shrub is damaged, dangerous, dead, diseased or dying.
To prune boxwood shrubs, use sharp shears to trim back any overgrown or dead branches. Shape the shrub by cutting back to a bud or branch junction. Avoid cutting into old wood as it may not regrow. Prune in early spring before new growth appears for best results.