Last Updated on September 16, 2021 by Grow with Bovees
You’ve planted arborvitaes (also known by its genus name thuja) or purchased property that already has established arborvitaes.
Maybe you’re dealing with a tree or small manicured hedges or shrubs.
You’ve got the watering and fertilizing down and understand the diseases and pests that can affect new growth and established trees alike.
But now you’re wondering how exactly to trim and maintain their shape while promoting healthy plants for years? How often and when to trim or prune? And what tools do you use on those branches and foliage?
By the end of this article, you’ll have a better idea of when the best time to trim and prune is, the best ways to trim and prune your arborvitae trees, how often you should trim and prune, what are the different types of tools you can use, and how to keep your arborvitaes’ foliage full and lush looking year-round.
So, let’s get moving to ensure your arborvitae evergreens meet their full, eye-catching potential.
Trimming vs Pruning
Before getting too far into the, ahem, weeds, let’s take a quick look at the difference between trimming and pruning. Some out there may think their meanings are interchangeable. However, that’s not necessarily true.
Think of it this way: when you have to get a haircut, you may say you just want a trim. You never say, “Looking for a good prune.”
In terms of plants, trimming is an overall way to encourage thriving new growth. It also helps maintain the shape, height, and attractiveness of your trees, hedges, and shrubs.
Do this by trimming new growth tips and green shoots. The shapes you choose to maintain also improves the appeal of your property overall.
Pruning, on the other hand, targets unwanted growth.
It includes specific cuts and doesn’t focus so much on cosmetics. Instead, it focuses your energy, attention, and resources on correcting an issue with a plant.
This usually involves reducing or removing branches due to disease or pests. Perhaps you have dead branches to deal with; a shrub whose branches are interfering with the growth of nearby plants; old wood that is rotting; or tall trees growing toward power lines.
Both trimming and pruning focus on the health of the tree or shrub. Trimming, though, also leans on cosmetic improvement, whereas pruning tends to be more specific in addressing certain adverse issues that may negatively affect your conifers.
When to Prune Arborvitae?
The best time of year to trim arborvitae is after the growing season, once the plant has gone dormant until the next growing season.
Essentially, this is the fall and early winter, depending on your local climate. Basically, you want to wait until you’re sure there will be no warm spells. So, after late November is a good rule to follow.
When Can You Not Trim Arborvitae?
You want to avoid trimming your arborvitae in the spring once the growing season has started. Any trimming after Saint Patrick’s Day should be avoided.
Instead, that’s the time to prune.
How Do You Trim an Overgrown Arborvitae?
You trim an overgrown arborvitae with simple tools like lopping shears (amazon link). Go one branch at a time, targeting new vice old wood. You may be tempted to use an electric trimmer to go faster, but a mistake or two can be easily made if you trim too quickly.
Instead, it’s better to go slower and monitor the shape as you proceed. This will ensure you don’t take off too many twigs or needles or take out larger spots than originally planned.
Better to focus on one zone at a time (top, middle, bottom) to ensure a good trimming experience without too many mistakes.
How to Reduce Height of Arborvitaes that are Too Tall?
Arborvitae trees can come in various sizes depending on type and through trimming and manipulation of shape.
You may want a tall tree, smaller shrubs, something more in the middle, like a hedge. However, if your tree becomes too tall for you to manage, there are a couple of things to take into consideration.
If you’re thinking of trimming arborvitae tops, you have to take into consideration if you want to eventually let them grow taller in the future or top-off a plant.
To do the former, simply trim new shoots around the central leaders, thinning them out but not totally flattening the tree.
To do the latter, you’ll have to make the call to basically flatten your plant out and cut out the central leader through a reduction.
The next tallest branches will become the leaders at that point, but maintaining the natural pyramid shape of your tree will become more difficult.
How to cut the top off is covered more below.
How do You Prune Overgrown Arborvitae?
There are two basic ways to prune an overgrown arborvitae. One is through branch reduction and the other is through branch removal.
With a reduction cut, you shorten the length of a branch by cutting it back to a thicker, sturdier part of said branch. With a removal, you’re doing exactly what it sounds like; cutting a branch completely off from the rest of the plant.
In both cases, the tool of choice is usually a simple set of pruning shears. Well, and a ladder if your arborvitae is tall. But you shouldn’t need anything beyond the pruning shears unless a branch to be removed is rather thick, then a pruning saw might be necessary.
When Should an Overgrown Arborvitae be Pruned?
The best time of year to prune your arborvitae is during the growing season, preferably in early spring and before late spring and the start of summer.
This allows initial new growth in early spring to give you a better idea of how the plant is shaping up, but before a rush of growth you might see in the waning months of spring. So, timing is important.
After mid summer, you can further refine the form before allowing it to settle in for fall and winter.
Beyond that, pruning should be done on a spot basis to deal with a broken branch or handle possible pests and disease.
Why Should an Arborvitae by Pruned?
The good news is that arborvitae trees don’t require much pruning.
It already has a natural pyramid shape. However, there are times it should be pruned to address such things as growth abnormalities, height and width, appearance, addressing blight, and reshaping due to wildlife interference.
For natural growth, you need to remember that arborvitae, with their pyramid shape, have a bottom that should be wider than the top.
However, if you’re having problems with deer eating leaves, then you might find your arborvitae with a heavier top than bottom. In cases like these, it may be possible to reshape the top through pruning to restore symmetry.
Side Note: arborvitae, genus thuja, is a coniferous tree, so it doesn’t really have leaves but flat needles that fan out from a central stem. However, they look like leaves from far away.
Arborvitae do not tolerate heavy pruning. So, you need to pick your reductions or removals wisely to not overstress the tree. This is where pruning branches that may also be stricken with blight or eaten by pests would serve two purposes.
Another good reason to prune is your arborvitae has gotten either too tall or too wide. If it’s too tall, you can reduce the height through a reduction.
If the width is too great or is interfering with the growth of neighboring plants, reductions and removals are recommended in moderation, first addressing branches afflicted with blight, pest damage, or are bare and showing no new growth (this is often a result of overcrowding, preventing sufficient sunlight).
If you need to address blight, it’s usually recommended to remove any branches, or parts of affected branches and destroy them to prevent spreading to healthier and more mature branches.
For reshaping purposes, try to keep your pruning to no more than 20 — 30% of an arborvitae’s foliage and keep the cuts to green wood rather than brown. Also, tackle vertical shoots that may be overshadowing lower branches.
Topping Arborvitae Trees — Is It Safe To Do?
Yes, you can cut the top off of an arborvitae but limit it to no more than a third in reduction. Any more than that, at a given time, could be harmful. Again, Thuja trees don’t require a lot of pruning and are not exceptionally tolerant of it. Too much at one time could be detrimental.
Also, cutting it off will eliminate upward growth from the original center and will give it a flat appearance. Be sure this is your intention, as the next tallest remaining branch will become the new “leader”. If your goal is to make your arborvitae into a hedge, then this is the way to proceed.
How do You Prune an Overgrown Arborvitae Hedge
You should wait until early summer to prune a group of overgrown arborvitae hedges and be completed by mid-summer. This will allow enough time to recover before heading into the dormant cycle, where you’ll once again be preparing for the process of trimming the limbs of your tree or trees. (See our guide on the best arborvitae fertilizers to make sure you’re using the correct products.)
Will Arborvitae Branches Grow Back?
If you have bare brown wood, those branches will more than likely not grow back. In the case of these specific species of tree, green is good (there is a chance new shoots and buds will grow) but brown arborvitae foliage is usually a sign the branch is done and should be removed.
There you go. The big basics of trimming and pruning your arborvitae trees.