The goal of pruning is to improve the overall health and usefulness of a plant:
Plant materials grown by a quality grower will have been pruned correctly from the start, so you shouldn’t need to worry about corrective pruning for a while. A good example is shrubs. Plant nursery staff work to encourage branching lower to the ground, so the plants don’t have voids and aren’t "leggy". For trees, the nurseries prune for nice straight single leaders and uniform, open branching.
After you plant your trees, you should pay attention to your plants as they grow and develop. Some corrective pruning may be necessary on trees to maintain a single central leader. As soon as you see another branch develop that is competing with the main stem, eliminate it right away.
Some species of trees will grow denser with more branches and you may want to thin out a few branches to allow more wind to blow through the plant for improved air circulation. Plants that have been thinned a bit also offer less wind resistance and may be less susceptible to storm damage as they grow and mature.
Pay attention to the overall shape of the tree. In many areas, trees can become windswept from the prevailing westerly winds. These winds may push branches to the east side of the plant. You may end up having to head back (or shorten up) a few of the longer branches if they develop outside of the normal length that you would like to see. Shorten up the branch by cutting it back to another branch or to another bud that will continue in its place.
If your tree gets damaged from wind or snow loads, selectively remove the broken branches by cutting them back to existing branches. Trees are pretty amazing in that if a large portion of a tree does get damaged, they do amazingly enough respond by filling in that part of the tree faster than you think.
If it flowers in spring, wait to prune. Don’t prune spring blooming shrubs in fall, or you’ll cut off all the flower buds.
Shrubs that bloom late winter or early spring are blooming on last year’s wood. Don’t prune them until after their flowers open, wither and turn brown next spring. If you wait for the flowers to finish and THEN prune, you will not eliminate any flowering.
Some plants that you should hold off pruning including Serviceberry, Magnolia, Redbud, Flowering Quince, Forsythia, Lilacs, Wisteria, Rhododendrons, Flowering Cherries and Crabapples, and early blooming Spiraea types. Enjoy the bloom and then do any corrective pruning if necessary.
There are a few shrubs which bloom on new wood and flowers will be produced in the new growth that develops in spring. Trim the Spiraea bumalda types like Goldmound, Goldflame, Froebelii, and all of the new Double Play selections back to about half way just before they start to grow. They will bloom wildly and after that set of flowers if you dead head them will bloom wildly again for you.
When you have a large, old shrub that isn’t flowering as well as it used to, or has outgrown its space, you may need to consider using the renewal pruning method. This method can take several years, but you’ll love the results.
In year one, you’ll prune out 1/3 of your shrub. Select the oldest, fattest stems and prune them right to the ground. This is called a thinning cut. Leave the younger thinner stems to remain.
In year two, you’ll select another 1/3 of your shrub to thin out. Again, select the oldest, fattest stems and prune them to the ground. Do the same in year three.
Renewal pruning is an excellent way to rejuvenate the shrubs without sacrificing the flowers or the fruit. This technique works beautifully for Aronia, Cotoneaster, Red and Yellow twigged Dogwood, Ninebark, Lilacs, Viburnums, Mockorange, Weigela, and shrub Willows. All of these plants should be maintained with stems that are younger than five years old.
Renewal pruning keeps the plants more juvenile, so they are less prone to disease, and produce more flowers and if the plants fruit – more fruit too. It also reduces the height and the plants are less leggy with more branches and foliage closest to the ground. Renewal pruning allows the plants to grow in their most natural form.
Sometimes shrubs need to have some stems shortened up. This pruning method is called heading back. It is used to reduce excessive growth to keep the overall size and form of deciduous shrubs.
It is important to use sharp pruning tools so the cuts on the plants are clean and smooth. Clean cuts heal fast.
Use bypass hand-held pruners and cut just above a leaf or needle at 45 degree angle. Try to keep the cut parallel to the branch. You want to avoid horizontal cuts, which can hold water and lead to problems down the road.
Heading back is also used for Japanese Yews and spreading Juniper types. Snipping back the longest new growth on these evergreens causes them to branch and encourages thicker new growth.
Hedges are living walls used to define an area, to screen off unsightly views, provide wildlife habitats, or even create barriers to dissuade any foot traffic. Hedges can be short or tall, sheared formal, or left untrimmed and natural no matter the size. Hedges are plants installed close enough together to allow them to touch. Each plant in the hedge will have foliage on two sides and the top.
For all hedge plants, it is important to always keep the bottoms of the hedge a bit wider than the top of the hedge. Hedges that are maintained wider at the base helps to keep the foliage healthy right to the ground making a nice solid screen. Plants that are wider at the tops can become leggy and open holes across the bottom, which defeats the purpose of a hedge.
Informal hedges are not sheared across the top and sides but are instead allowed to grow naturally. Lilacs make classic informal hedges in open sunny areas. Some other plants that would work well as an informal untrimmed hedge should include Weigela, Viburnums, Forsythia, Hydrangeas, Rhododendrons, and Azaleas.
Formal hedges are plants that are planted close to each other and then sheared wider at the bottom and narrower at the top. Some classic hedge plants include Privet, Boxwood, Burning Bush, Holly, Distylium, and Arborvitae to name a few.
These plants will need to be sheared to maintain a more formal look. Electric shears are helpful tool, but please don’t forget the fundamentals of pruning. If you only rely on electric shears, you’ll eventually have a plant with a lot of exterior bud growth, but a dead interior.
Be sure to thin the interior of your plant regularly by cutting dead branches off at the ground to rejuvenate the plant. Plants need light and air, so selectively head off branches by hand all along the entire length of the hedge.
Some plants like a burning bush puts on only one flush of growth in the spring and that is all they will grow that season, so they only need shearing one time. Others like Privet may need trimming several times to keep the plants looking neat and tidy.
Use the Candle Pruning method to prune pine trees. When the spring temperatures start the pine trees to start putting on new growth, the tips of the branches elongate, and it resembles a pencil.
To keep pine trees small, this new growth should be broken about in half with your fingers. Do this in spring before any green needles show on that new growth.
Breaking the new growth doesn’t harm the emerging needles. It simply lets the new bud to form and shortens up the finished growth by about half for the season.
Love pruning? Try your hand at “Ninja Master” level techniques, which includes Bonsai and Specialized Topiary.