Taxus trees naturally have distinctive growth habits and do not require excessive pruning to maintain shape. Pruning is done to reduce the size, such as with yew hedges. This is a regular, light pruning done anywhere between early spring to the middle of summer, as suggested by Duncan Coombs in "The Complete Book of Pruning." Iowa State University Extension recommends pruning yew shrubs before new growth begins, as recommended by the Iowa State University Extension.
When pruning yew shrubs with upright growth forms, thin the branches by making cuts underneath the overhanging plant foliage. Shape the plant with a general tapering from top to bottom. If the yew has a naturally spreading form, create more emphasis on the plant's naturally shingled look. In order to maintain the taxus yew hedge's compact look, shear away the new summer growth during early spring.
Times to Avoid
It is best not to prune evergreen conifers such as Taxus yew during late summer or early fall. Late season pruning encourages the trees or shrub to produce succulent, new growth that does have enough time to harden off or mature before the cold season. This new growth becomes prone to cold and frost damage, as cited by the Virginia Cooperative Extension.
There are certain times when yews require corrective pruning. This situation arises when branches are diseased, have pest infestations or damaged beyond repair. Prune to remove sick or damaged plant areas at any time of the year. This keeps the disease or pests from spreading to other tree areas. When removing sick plant areas, make the cut several inches below infected wood and disinfect pruning tools between cuts.