Pruning is a necessary practice for most plant materials. Proper pruning is very important to plant growth. In order to prune plants properly you must know what plant you are pruning, its growth habit and it’s flowering time.
Flowering Shrubs that bloom before June 1, must NOT be pruned in the spring. These plants such as forsythia, magnolia, wisteria, rhododendron, azalea, lilac, bridalwreath spiraea, redbud and flowering dogwood must be pruned after they are finished flowering. You can prune them for shape, to thin them or to severely remove overgrown stems after they have flowered but then not pruned again for the year!!
Flowering Shrubs that bloom after June 1 can be pruned in spring but if you miss that window of time they can be pruned after they have finished flowering that year. These plants bloom on new wood produced in the growing season.
There is another group of plants that require severe pruning in the spring. These are plants that re-grow quickly in one season. Butterfly Bush, Bluebeard Caryopteris and roses fall into this category. They should be treated like perennials in this way.
Conifers are difficult to explain as a group because so many of them have specific pruning practices. As a rule conifers should be pruned before July 1 or not until after October 31. This gives the plants time to harden off any new growth that has occurred during the growing season.
The pine family prefers candling in early spring to pruning whereas the yew family can be sheared or pruned severely. Spruce, fir and junipers do not like severe pruning and it must be done very lightly on new growth only.
Shearing is a different practice altogether and should only be done on plants that are being used as a hedge or topiaries. It is important to find out the plant types that will tolerate shearing before using this type of pruning practice.