What’s the Best Shape for a Thuja Hedge?

Thuja Green Giant is the most popular hedging plant there is, for all but the coldest areas. Many people are planting it, and then asking themselves exactly this question – what is the best shape for me to train me hedge into? The answer is not difficult, although there are some things to think about, and how to achieve the best result it is also something to consider.

The Best Shape for a Thuja Hedge

  • Narrower Top than Bottom – it just looks so much better
  • Rounded Top – If you get snow in winter
  • Sides sloping inwards – lets light to the lower branches
  • Flat, not bulging – keeps the lowest parts living for the longest time
  • Keep the top horizontal – for that perfect look

Narrower Top than Bottom

Your hedge will tend to grow faster and more vigorously in the top few feet, than it does lower down. All the water and nutrients are sucked up there, and the bigger that part grows, the more it will take everything away from the lower parts. That way, in nature, it will make a tall tree with a trunk – keeping its branches safe from grazing animals. But we don’t want that, we want green all the way to the ground. We need to control that vigorous upper growth more than the weaker lower growth, to keep a good balance. When you trim, if you find yourself taking several inches more from the upper sides and top, than you do lower down, then you are doing it right. Another practical reason for keeping a narrow top is that it greatly reduces the risk of your hedge splitting open under a heavy snow fall, or even in fierce winds. A big, fat hedge is much more likely to break apart than one that is slim and upright. It is clipping that keeps it dense, not thickness. The more you clip, the denser your hedge will be, even if it is only a foot wide.

Rounded Top

This is a perennial discussion topic among hedge growers – should the top be rounded, like half a circle, or trimmed square, with a flat top, and crisp corners? Many people find the square look more attractive, especially if you have a formal-looking garden. If you can keep the top thin – just 8 to 12 inches across, then a square top will be fine. In warmer areas it can be thicker, but if you get a lot of snow where you live, especially the wet, heavy kind, then it will stick on that flat top and build up. The weight can bend and snap branches, ruining the profile of the hedge you so lovingly created. If you anticipate that problem, then rounding off the top, while still keeping it thin, will encourage snow to slide off before it gets too heavy and does damage.

Sides Sloping Inwards

If you are making a neat hedge, it seems to make sense that you would have the sides exactly at ninety degrees to the ground. It makes sense, but it is not the best idea. A perfectly straight hedge will throw too much shade onto its lower parts, and they will not get enough light to keep them growing vigorously. If you slope the sides in a little, just a few degrees, which will only show if you stand exactly at the end and look along, then more light reaches the bottom. This means that those lower branches stay healthy and green for many, many years, giving you a green wall right to the ground.

We talked in a blog a few weeks ago about how to get that angle perfect, all along your hedge. This give the best professional look, and it is not hard to do. To quote that earlier blog:

Take three pieces of wood, one 6 feet long, one 3 feet long and one 6 feet 8 ½ inches long. Join them together to make a triangle. You will see it has a right-angle in one corner, but if you attach the 6-foot piece at a point 6 to 7 inches inside the corner of the 3-foot piece, that 6-foot piece will make an angle of about 80 degrees to the vertical, not 90 degrees. If you hold the resulting triangle up to the hedge, with the small piece horizontal on the ground, that is the perfect slope for the front of your hedge. Just lean it against the hedge as you trim, and you will always keep the same slope, no matter how big your hedge is.

Sounds a bit tricky, but it’s just a few minutes work. Once made, you can keep this guide forever, and always have the perfect hedge. For a shorter hedge, you can usually judge the slop by eye. Doing this will also solve problem number one – the top will automatically be narrower than the bottom.

Flat not Bulging

Keep the sides flat as well as sloping inwards. Letting it bulge in the middle, and trimming the bottom so it is rounded inwards, is a mistake that will only encourage the bottom to die out, leaving bare stems where you want lush green right to the ground.

Keep the Top Horizontal

Especially if you have a sloping garden, don’t slope the hedge to follow it. Keep the top horizontal for that perfect look. Use a tightly-stretched string, and a line-level (a small gadget from the hardware that hooks onto a string) to get it perfect. The human eye is very, very good at judging horizontal, and a drunken hedge sloping up or down is very disconcerting! If you have a very sloping garden, and you are going to end up with a difference in height of more than a few feet, consider stepping the hedge down in two or three sections, with a nice vertical spot where the level drops. That is so much better than an irregular top, and just as easy to maintain, once established.


If you follow these basic rules, your hedges will be the talk of the neighborhood. Remember to start trimming almost as soon as you finish planting. Don’t make the most basic mistake of all, and wait until you reach the final height before starting to trim. You will get the sturdiest, healthiest and densest hedge by trimming regularly, but lightly, while the hedge is growing up.

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