When Can You Trim Trees?

The services of an arborist may be required for extremely tall trees.

Pruning is the practice of altering the shape, growth habit or the innate structure of a plant. It is done either all at once or over a period of time, which is called training. Pruning can be done at any time, but it is best done when the tree is not actively growing. A tree's first pruning is generally done at planting time to give it a strong structure and remove any problem wood before it gets too big.

Before You Start

The most important aspect of pruning is the implements used. You should fit the tool to the job so you don't have to work as hard and the tree sustains no damage when cut. Hand pruners are suitable for small wood up to 1/2 inch, while the anvil pruners can handle 3/4-inch wood. Loppers and hand saws are good for 1- to 2-inch stems. Hedge clippers are only for soft wood and leaves, and are used for shaping. Pole pruners and other types of cutting tools are appropriate for large limbs. Always sharpen your blades and make certain they are clean to prevent the spread of pathogens.

When to Trim

Trimming or pruning plants is usually done in late winter to early spring. It is best to trim before the plant has fully leafed out if it is deciduous or you will be cutting off the foliage. The same holds true for plants that will flower. If you cut too late, you will ruin the color display and perhaps any fruit that follows. Additionally, most plants are dormant in winter and don't begin to grow again until temperatures reach consistent levels around 60 degrees Fahrenheit. This means that cutting them will not interrupt sap flow or subject them to serious stress. There are fewer pathogens to get into cut surfaces in late winter, which minimizes the tree's risk of infection.

Basic Trimming and Pruning

Trimming generally serves the purpose of keeping the shape of a tree. Most trees require a bit more than that, and this is called pruning. Trimming uses hedge clippers or shearing blades to skim over the plant surface and remove smaller out of place growth. The effect is smooth and even. It is appropriate for most evergreen hedges. Pruning is a cutting process in which each piece of wood is selected for removal one at a time. It is more time-consuming but generally better for the tree, as it does not use indiscriminate cutting of potentially healthy material to achieve the goal.

The Process

Trimming uses a smooth non-stop motion to create an even surface. Hedge trimmers are hand operated, while the gas- or battery-powered shears do not require manual energy. Whenever possible, it is best to leave the tree in as natural a shape as possible. This means cutting out broken and diseased wood and thinning the crown so light and air can enter. The tree should also be limbed up, a process by which you remove any wood that impedes pedestrians or other moving objects, including the lawn mower. Topping a tree is not recommended. It is dangerous in very large species and the exposed crown is open to environmental damage. It is best to chose trees that will fit into your landscape and plan for their height requirements.

References

• University of Minnesota: Prunign Trees and Shrubs; Mike Zins and Deborah Brown
• United States Federal Forest Service: How to Prune Trees
• Aggie Horticulture: Proper Pruning Techniques; Douglas F. Welsh, Everett Janne