These are Thuja Green Giants.
Typically, if you plant two conifers close to each other, growth where the trees contact each other becomes restricted.
The other parts of the tree continue to grow as usual.

Thanks for the picture! My issue is that at one end is a fence and the other has boxwoods. This is in the 20 ft area. I want a screen but don't want to crowd the area. If I plant 5 ft apart then there is 7.5 feet at each end. Will this be enough or should I just plant 1 tree? Thanks for the help.

If you put two 5ft apart, it's likely they will eventually reach the fence and boxwoods if left unchecked.
A single planting might do the same, although it would take longer to get there.
If you're so inclined, Green Giants can be pruned with good results, which can expand the possibilities.

"...these trees get 12-20 foot wide, ...", WOW.
My neighbor put three of them just a foot over the property line on his side 15 years ago. I am pruning them now on my side to keep them 3 ft to their center. They did loose some branches over winter, hopefully more!

sluice,
Thanks for your response.

If I choose to plant the 2 arbs 5 feet apart, can you advise me on the trimming? I know these trees get very tall. Do you recommend cutting the top to stop the growth when it is about 15 feet tall? I just don't want to let it grow tall and I can only trim around the tree only so far up. It sounds like I can plant the two arbs, just be prepared to trim them later on to keep them in line. Thanks for any advise.

bellily,

I would say start early by trimming a little bit here and there, to get familiar with how your trees respond to the pruning.

Here are some other green giant pruning tips.

This first is from ehow. The second, also linked below with pics, is from landscapeadvisor.

Ehow (Brenda Priddy)

Green giant trees are one of the fastest growing evergreen bushes. Often used for privacy between property lines, the green giant also can be trimmed to look like a traditional hedge. The green giant tree grows to around 60 feet tall, making it one of the tallest evergreen bushes in the world. Green giant trees require very little pruning, but many people choose to prune them into a desired shape and height. With a few tools the green giant tree can become the perfect hedge.

Difficulty: Moderately Easy
Things You'll Need: Work gloves, Goggles, Hedge clippers, Tree saw, Ladder, Trash can

1
Decide what you want your hedge to look like. Some people prefer their green giant trees to grow individually, and others prefer for the trees to grow together. Green giants grow 3 to 5 feet a year, and can reach 60 feet. In most cases 60 feet will be too tall for the environment, so the trees need to be trimmed every year.

2
Cut away any dead or dying branches. As an evergreen, the tree can be pruned at almost any time of the year. Fall and winter are the best time for pruning, as the sap isn't running at that time. Cut away any branches that show signs of disease. Place the diseased branches in the trash can or set aside for burning.

3
Cut green giant trees to the height and shape desired. If you want the trees to look more like trees, trim branches that are too close to nearby green giant trees. Taper the top of the tree towards a point, creating the look of a traditional evergreen tree.

4
Cut the top of the tree off if you want the trees to grow more like one solid hedge. Allow the separate trees to grow together along the sides. Flatten the top to a uniform shape. Trim the sides of the tree so that it is flat and uniform as well. Be careful not to cut too much off the top, or the tree may have a hard time recovering from the cut--1 to 2 feet per pruning is enough to make a difference without damaging the tree.

Landscapeadvisor (Roger)
The Green Giant Growth Habit
Perhaps I've said it before, but itis extremely helpful when you know what a plant's growth habit is before you prune. Growth habit is basically the shape a plant naturally wants to grow into and how the branching structure supports that shape. For example: Arborvitae Green Giant is pyramidal in form and proportionately much taller than wide. As a matter of fact, this plant will easily get to 30Âft tall and 15Âft wide in thirty years. Rapid growerÂ- I think so. Its branching structure is horizontal with some ascending branches as well.

Other characteristics about the plant can be helpful too when deciding your pruning strategy. For instance, Arborvitae ÂGreen Giant prefers more light (full sun is ideal). The less light it gets the thinner and more open its branching and foliage will be. Prune less aggressively if you know the plant is adapting to less than ideal conditions.

Before Pruning
The Pruning Strategy
LetÂfs assume the ÂeGreen Giant youÂare going to prune has been positioned to have enough room to grow and stay somewhat within its Ânatural boundaries. If the space is too limited and thereÂis no future for the plant in that spot, think about transplanting it.

To give Green GiantÂa strong trunk and branching structure, itÂis important to prune them in their early years. In the first picture above, these Arbs were undoubtedly pruned early on in their lives. Notice how full they are from the ground to about 4/5ths of their height. However, the last growth at the top is thin and Âstretched-out. This is very typical of rapid-growth plants.

It is this top growth (upper 1/5th) that needs pruning. You should also scout the lower portion of the plant for any branch ends that may have grown more aggressively than others. There should not be many.

After Pruning
I apologize for the picture quality of these Âbefore and Âgafter shots, but even the silhouette conveys the degree of pruning I did.

I used a traditional trimming shear along with an orchard ladder. By today's standards you might call that old school. I still think a good quality hand shear gives the best cut and, of course, with total control. I did, however, think how convenient and productive a telescopic gas powered shear would have been. Just take care as those power shears can cut aggressively.

The main goal and concept here is to trim the ends of the longer, fast growing branches to shape the plant and encourage fuller growth.

This is what plant nurseries do while theyÂare growing the plants for market. You want to continue this trimming routine for as long as it is practical. The idea is to develop a full, nicely shaped plant so that it can continue to grow on its own with this strong foundation you help create.

Thanks sluice for the post. Great information to study. It sounds like I can plant 2 trees at 5 foot apart and trim them as needed. It sounds like I should probably cut them off at 15' in height so I can trim the tree with a ladder.

In your opinion, as long as they stay trimmed, I should NOT have a problem with crowing in that area? This would give 7.5' from the fence and 7.5' from the boxwoods. And, I get a living hedge.

Thanks again.

I continued my neighbor's 3 monster Green Giants with 2 Emerald arborvitaes for privacy. I did not want to prune at all, but now got stuck pruning my side of his Green Giants.

Emeralds get only 4 ft wide and 15 ft tall in perhaps 20 years. So far they behave well, never needed to prune them, they never lost a branch. So, why do you want to plant baby monsters and then prune them for life on high ladders?
Bernd

Berndnyz5,
Thanks for your follow-up and question. Here is my story. I have 35 emerald green arbs that have been planted along both sides of my property. They were planted 3 feet from the fence and 4 feet apart. In regards to the Green Giants, I wanted to plant these at the back of my property. There is a hill there so I am unable to grow grass there.

I am OK with not prunning the Green Giants assuming they don't get to wide (don't care how tall they get). I plan on planting the two trees 5 ft apart. This leaves 7.5 feet on each side.

Questions for you or anyone else(as you are familiar with these arbs):
1) Based on your neighbors green giants, how wide are they?
2) Is my spacing of 5 ft apart for the two trees to leave 7.5 ft on each side OK. Or maybe I should do 6 ft apart to leave 7 ft on each side?
3) If I don't prune the GG, will I be OK? Or should I just plant one (at the 10 ft center of the 20 ft area).
3) Regarding your emeald greens, how old are they, how tall and wide?

Thanks for your comments!!! Just want to plant right the first time.

bellily,

It might depend on what is considered crowding, but in general so long as you're trimming them, you'll be able to shape them as desired.

My situation is very different to yours, you have the space. Green Giants seem to be a tree people do not realize in what they are getting into. My original neighbors are long gone, the next ones (and I) found the Green Giants still OK, the present neighbors might find them too big too, but in 10 years from now : very big. I have a C. nootkatensis pendula close to it, and am condemned to prune the Green Giants forever.

1. They are about 10 ft wide, and perhaps 20+ft tall. They are spaced about 12 ft apart, have now a 2 ft gap in foliage between them.
2. This is really your choice.
3. Can you predict how much time you will have to spend on your landscape 10 years from now? Perhaps you will have no time, except for mowing the lawn? I personally love to work in the yard, prune here and there, but placing two Green Giants in that spot would create too much future work for me. When you place one tree in that spot, you will never need to prune it to keep its shape. (except for broken branches).
4. My 2 Emeralds are 10 ft tall, 2 1/2 ft wide, were planted about 5 years ago, and are good looking neat trees.

Good luck!
Bernd

Hello again,
Thanks for all your comments. I think I will just plant one arb for now at the 10 ft center of the 20 ft spot. I don't want to prune if I don't have to. Also, I hear that this tree should be planted by itself - neat tree.

I was wondering when it gets tall - what about bagworms? These could kill the tree. I assume that if I see bagworms, I would need a professional to come out to spray(as I could not get that high up). Maybe I should stop the growth when it gets so high? Any recommendations?

Thanks again for the help.

My trees have gotten too tall for the spot and now the top is bending over. Can I cut them off at the bend and will it grow back?
Thanks.

I’m about to have 3’-4’ Green Giant Arbovitae installed as a privacy fence along our property line. Spacing will be 5’ but I’m curious as to how far off the line I they should be planted. In the responses above I’ve read these plants can be between 4 ft and 10-20 ft wide. That’s a large difference. How far off the line should they be planted (in zone 6b)?

This is not a particularly narrow or columnar form of arborvitae and will not stay at a 4' width unless pruned or sheared. I'd expect to see at least a 10' spread but in my area, 15-18' is not uncommon. I'd allow a least 4' from the property line but if you need to not exceed any boundaries, pull them out another foot or two.

Mine are 13 yrs old, and about 5-7 ft wide now at the very bottom. Actually rather narrow compared to say, Leyland cypress. So how long are you going to be at the same place?

No plans to move at all- just want to block the view beyond our property, just not wanting a shrub line wider than 5-8 feet.

It's not called 'Green Giant' for nothing.

The U.S. National Arboretum presents Thuja 'Green Giant', a large, evergreen
sentinel in the landscape

http://www.usna.usda.gov/assets/images/as_standard_image/Thuja_Green_Giant.pdf

and says it's Landscape Use is as an

Evergreen screen or specimen plant for parks or large landscape
settings

But to your point, the pic in your link shows a pic of a ‘giant (tall)’ bush that appears to be 5’8’ wide, not 15’-20’ wide

And it is also not at full maturity so not 60' tall......maybe not even 30' tall as far as I can determine from the photo :-)) The link clearly states a width of 12-20' at maturity.

FWIW, neither of the parent plants are particularly narrow in form so no reason to assume the hybrid will be significantly narrower.

Thanks!