Spring is pruning season, and it’s best to get it done sooner than later for many plants. You should prune many trees and shrubs in late winter or early spring, while they’re still dormant. But there are also a few that you should not prune in early spring.
Pruning can be intimidating, but it’s not as difficult as many people expect it to be. This pruning guide will help you know when and what to prune, what not to prune, and how to prune properly in central Iowa.
When & What To Prune
Generally, you should prune most deciduous and fruit trees and shrubs in early spring while they are still dormant. For central Iowa, that’s anywhere from the end of February until mid-April. Trees and shrubs that you can prune in early spring include:
- Rose of Sharon
- Knockout roses
- Tea roses
- Large leaf hydrangea
You should prune early spring-flowering shrubs immediately after they finish flowering in late spring or early summer. These include:
What Not To Prune
Some shrubs don’t need annual pruning; you can leave them for several years in a row. These shrubs include:
- Burning Bush
- Summer Sweet
- Panicle hydrangeas
Rhododendron and azalea are shrubs that don’t require pruning at all.
Do not prune maple, birch, or elm in late winter or early spring. Their sap is flowing heavily then, and they will “bleed” a lot of extra sap. It doesn’t harm the tree, but it can be messy, and it will take longer for the wound to heal.
Do not prune oak trees in spring. Beetles that carry oak wilt are active in spring, summer, and fall. The safest time to prune oak trees is in winter, between November and February.
How to Prune
To make sure you get your pruning done well, you’ll need a few different types of pruning tools, which you can pick up at the garden center:
- Hand pruners for small branches up to .5 inch in diameter.
- Loppers, for larger limbs up to 1.5 inches in diameter.
- A pruning saw, for extra large limbs, over 1.5 inches in diameter.
Staying safe while pruning is essential. If you’re looking up into a tree and cutting above your head, it’s surprisingly easy to end up with sawdust or wood chips in your eyes. For pruning its best to wear:
- Long sleeves
- Long pants
- Work gloves
- Safety glasses
If you’re dealing with larger limbs, you should have a hard hat, but that’s the time to call in professional arborists to tackle the job.
Pruning for Fastest Healing
When you prune your trees and shrubs, make clean, angled cuts so that they heal as quickly as possible. In most cases, you’ll want to cut at a 45º angle, so water doesn’t sit on top of the cut and cause rot.
When you’re removing large limbs, it’s best to start at the tip and take the stem down in shorter chunks so that you have less chance of causing any tearing. Aim for pieces that you can easily handle, 1-2 feet long, is good. It’s also important to undercut large limbs just above the branch collar to avoid tearing.
How Much to Prune
It’s easy to get carried away in pruning and over-prune your trees or shrubs. The general rule of thumb is to never remove more than 25% of a tree or shrub’s total volume in one year.
When you first start pruning your trees and shrubs, look for the 3 D’s: branches that are damaged, diseased, or dead. Remove these types of branches first, then step back and take a look at your tree or shrub and decide if it needs more.
For most trees and shrubs, that will be enough. But for fruit trees or ornamental trees, you may want to open up the tree’s crown to let more light and air movement in, which will help your tree produce better and prevent disease.
How to do Rejuvenation Pruning
There are a few exceptions to the 25% rule, including shrubs that benefit from rejuvenation pruning every 3-5 years. Rejuvenation pruning means cutting back a significant amount of the shrub to encourage it to focus on fresh, new growth.
In many cases, rejuvenation pruning means cutting a shrub right down to about 6 inches tall. This encourages new, young growth to shoot up. It will take a few years, but before too long, your shrub will be blooming or fruiting like a young shrub again.
Hedges should be pruned 1-2 times a year, in spring and mid-summer. Prune your hedges to be slightly wider at the base than the top, at a slight angle, so that the leaves and branches at the bottom also receive plenty of sunlight, and don’t become leggy and sparse.
Have Spring Pruning Questions?
It’s always better to ask a question before you start pruning than after! You can ask our staff at the garden center for pruning advice, or you can send a quick email to the local Iowa State University Extension office.