Timing is an important factor when pruning plants in the nursery or the landscape. The late dormant season is best for most pruning, with some exceptions noted below. Pruning in late winter, just before spring growth starts, leaves fresh wounds exposed for only a short length of time before new growth begins the wound sealing process. Another advantage of dormant pruning is that it's easier to make pruning decisions without leaves obscuring plant branch structure. Pruning at the proper time can avoid certain disease and physiological problems:
To avoid oak wilt disease DO NOT prune oaks from April to October. If oaks are wounded or must be pruned during these months, apply wound dressing or latex paint to mask the odor of freshly cut wood so the beetles that spread oak wilt will not be attracted to the trees.
To avoid increased likelihood of stem cankers, prune honeylocusts when they are still dormant in late winter. If they must be pruned in summer, avoid rainy or humid weather conditions.
Prune apple trees, including flowering crabapples, mountain ash, hawthorns and shrub cotoneasters in late winter (February-early April). Spring or summer pruning increases chances for infection and spread of the bacterial disease fireblight. Autumn or early winter pruning is more likely to result in drying and die-back at pruning sites.
Some trees have free-flowing sap that "bleeds" after late winter or early spring pruning. Though this bleeding causes little harm, it may still be a source of concern. To prevent bleeding, you could prune the following trees after their leaves are fully expanded in late spring or early summer. Never remove more than 1/4 of the live foliage. Examples include:
- All maples, including box elder
- Butternut and walnut
- Birch and its relatives, ironwood and blue beech
Trees and shrubs that bloom early in the growing season on last year's growth should be pruned immediately after they finish blooming:
- clove currant
- flowering plum
- or cherry
- early blooming spirea
Shrubs grown primarily for their foliage rather than showy flowers should be pruned in spring, before growth begins:
- alpine currant
- burning bush
- purpleleaf sandcherry
Shrubs that bloom on new growth may be pruned in spring before growth begins. Plants with marginally hardy stems such as clematis and shrub roses should be pruned back to live wood. Hardier shrubs such as late blooming spireas and smooth (snowball) hydrangeas should be pruned to the first pair of buds above the ground.
Use the right tools for pruning
The right tools make pruning easier and help you do a good job. Keeping tools well-maintained and sharp will improve their performance. There are many tools for pruning, but the following will probably suffice for most applications:
A good pair of pruning shears is probably one of the most important tools. Cuts up to 3/4 inches in diameter may be made with them.
Lopping shears are similar to pruning shears, but their long handles provide greater leverage needed to cut branches up to 1 1/2 inches in diameter.
Hedge shears are meant only for pruning hedges, nothing else. They usually cut succulent or small stems best.
Hand saws are very important for cutting branches over 1 inch in diameter. Many types of hand saws are available. Special tri-cut or razor tooth pruning saws cut through larger branches – up to 4 inches in diameter – with ease.
Pole saws allow for extended reach with a long handle, but they must be used carefully as it is difficult to achieve clean cuts with them.
Small chain saws are available for use on larger branches. Operators must wear protective clothing and exercise caution when using them. Never use chain saws to reach above your shoulders, or when you are on a ladder.
Source: University of Minnesota Extension