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Thin out plants to let more light into the center of the plant.
Thin out plants to improve air circulation around the plant, making it less susceptible to pests and diseases.
Remove diseased branches.
Remove crossing branches that will rub against each other and leave the plant vulnerable to pests and diseases.
Remove weak branches that will get torn off in wind and snowstorms.
Rejuvenate old plants to restore vigor.
We prune for size:
To keep plants within their space in the garden.
To keep flowers at a reasonable height for your enjoyment.
We prune for structure/appearance:
Display ornamental bark.
Improve form or display branch structure of tree or shrub--create a more beautiful plant.
Redirect growth of plant--encourage it to grow in a chosen direction.
We prune for flowers and fruit:
Prune for more fruit and flowers.
Prune for fewer but larger fruits and flowers.
What are the best tools?
Choose sturdy, safe, well-made tools with sharp blades and be sure you have the right tool for each pruning job. This does not necessarily mean buying the most expensive tools. Ultimately, you will need to choose tools that suit your gardening style and work for you.
Keep your tools clean, sharp and ready to use. Most tools can be easily cleaned by wiping with a rag after use or cleaning with WD-40. Don't leave your tools out in the rain! Sharpen with a file or take tools to your local garden center for care. If cutting diseased wood, clean your tools with rubbing alcohol to avoid spreading disease from one plant to another.
Here is a list of some basic pruning tools:
Bypass pruners: A good pair of bypass pruners is one of the most useful garden tools for small pruning and all sorts of general garden work. They will cut through a ½ to 1 inch thick stem. Many brands have replaceable blades and can last for years.
Lopping shears or loppers: These come in different sizes and will cut branches up to 1½ inches thick. They are very useful for large shrubs and small trees.
Pruning saws: There are many types. Folding saws are easy to use and very safe (if you make sure to lock the blade into place). Their small size makes them useful for getting into tight places and for cutting small to medium-sized branches, about 1½ to 3 inches thick. -- Fixed blade saws are best for larger branches on larger plants.
Hedge shears: Choose ones that are comfortable to hold; pruning a hedge is tiring.
Electric hedge shears: These are fairly easy to use. You usually need a long extension cord. Again weight is a consideration
How do plants respond to pruning?
A plant's response to pruning depends on the plant and how you make your cut. Here are 3 basic techniques:
Pinching: Simply pinching out the top growing point of a plant is one way of pruning your plants. Removing the top slows down the top growth of the plant and induces side shoots to grow. One of the most familiar examples is pinching chrysanthemums to produce bushier, more compact plants. Lanky houseplants also respond well to pinching, as do sweet potatoes and tomatoes.
Heading: A heading cut is one that shortens a stem. Just as in pinching, the cut will stimulate side shoots to grow. A small cut will encourage many buds on the stem to grow; larger cuts will produce fewer yet larger side shoots. These cuts should be made when you are trying to fill out a plant. Shearing a hedge is one example of making heading cuts.
Thinning: If you would like to thin your plant to allow more light or better air circulation, you'll need to make a thinning cut. In a thinning cut, you remove a branch in its entirety. This prevents any re-growth. Thinning old garden roses to encourage better air circulation is a classic example of a thinning cut.
When do we prune?
In our climate February and March, before new buds break, is usually the best time to prune a shrub or tree. And it's also a good time to study the structure and condition of a tree or shrub, so you can decide how and where to prune.
There are plenty of exceptions. Here are 2 main reasons to wait until early or mid-summer:
Shrubs that flower on old wood (last year's growth) should be pruned after they flower.
Shrubs that flower early in the season should be pruned after flowering. In the case of shrubs that produce interesting fruit, remember that you'll be cutting some fruit off for the season.
What is the correct way to prune?
The most important thing when pruning is to understand the natural shape of a tree or shrub, so that you can work with it to make it look its best. Some shrubs have a mounding habit, while others tend to grow upright. Working with the plant's natural form allows you to create beautiful, architectural specimens.
Reminder: Choose the right plant for the right place. Know the plant's shape and mature size before you introduce it into your landscape. Pruning will allow you to contain a plant but will not transform a 12-foot monster into a 4-foot dwarf.
Cut above a bud (at least ¼ inch above)
Cut at an angle away from the bud (generally a 45°angle) to ensure that water runs off the cut and doesn't rot the new bud.
When removing a larger branch (more than 1½ inches), follow the 3-cut rule to avoid tearing the bark. Your first cut is underneath the branch, 12 inches away from the final cut. Cut through ¼ of the wood. Next, cut off the branch several inches further away from the final cut, cutting from above. Finally, cut off the remaining stub, making sure not to cut into the branch collar (regenerative tissue) where the stem adjoins the trunk.
The general rule of thumb for pruning a shrub is that you take off no more than 1/3 of the material, and for trees no more than ¼ of the live foliage. Unless you are planting a hedge, you generally only remove dead and diseased wood the first year and begin pruning after the plant has become established. Many trees and shrubs need little pruning--just an occasional shaping and cleaning out of dead material.
For rejuvenating old shrubs, follow the rule of threes: over the course of 3 years, remove 1/3 of the old wood on the plant each year.
Another, more extreme form of rejuvenation pruning is to cut the majority of the shrub back hard (to within 1 to 2 feet), leaving at least 2 branches intact with foliage so the plant can photosynthesize. This should be done in March to induce maximum growth.
Make sure you know your shrub before you do this. If you cut forsythia back hard, it will re-sprout into a tangled mess. This extreme type of rejuvenation is often done when there is an appreciable amount of damage on the shrub (e.g. winter sunscald) or when you are giving an old shrub one last chance to start performing again.