Choose a warm, bright place out of direct sunlight to work.
A good rule of thumb is that if the plant blooms on new growth, it can be pruned in winter, before the new season's growth begins and after the final bloom of the year. Be careful with spring-blooming shrubs- those usually can't be pruned in winter without damaging the flower buds and ruining the blooming season.
Dec 10, Plants grown for their colourful winter stems, such as dogwood, Cornus alba, and white willow, Salix alba, should be cut back hard or ‘stooled’ in late winter or early spring, to around 15cm above ground level. Other shrubs should have the thinnest, spindly growth removed. Oct 19, In areas with ice storms and severe weather that can break plant material and cause damage to the structure, butterfly bush can be severely pruned and it will not adversely affect the flower display.
Removing errant stems and growth will help prevent more acute damage from winter weather and is a sensible way of preparing butterfly bushes for winter in any region.
Be careful with spring-blooming shrubs- those usually can't be pruned in winter without damaging the flower buds and ruining the blooming season. (So don't even think about taking the shears to your azalea, viburnum, spirea, lilac, rhododendron, quince, loropetalum, and forsythia in winter!) Those you should prune immediately after blooming ends.
Hi, Deborah: Thanks for this excellent question. FWIW, what you describe sounds less like pruning and more like tree work necessary for the sake of bushnotch.bar that as it may, most deciduous plants are dormant during winter and perfectly OK to actually prune to get rid of dead wood and encourage new growth in spring.
How dormant the tree is, or even whether it’s dormant at all, would depend on.