Screening is often high on the list of garden projects for many people, especially if you live in a built-up area. Evergreen screening is an effective and low-cost way to screen out unwanted noise, an ugly view, or neighbors, especially if you need screening above 6 feet. Tall fences are expensive, difficult to erect, and are often prohibited by city by-laws, but planting is not. You can put in screening plants that will grow pretty much as tall as you want, and a popular choice for that is Thuja Green Giant. There are lots of good reasons for this – perhaps the most obvious is the rate of growth – so let’s consider this choice in more detail, to see if it’s the right one for you.

Do You Have Enough Room?

Thuja Green Giant will grow, if unclipped, to a height of about 30 feet, and while that might take 30 years, it will be half that height in as little as 10 or 12 years. The bigger trees get, especially in a long screen, the more difficult and expensive it is to trim them, so the first thing to think about is the effect of planting a green wall, 20 feet or more in height? What about light into your home and garden? That will depend a lot on how close to your home the screen is going to be, and of course whether it is to the north or south, or some other compass position. Tall plantings to the north side will not cast a shadow, while in other positions it will. Consider too that the shadow will be longest in winter, because the sun is lower in the sky, and that may be just when you want that extra light.

Remember too that Thuja Green Giant will be up to 12 feet wide in time, again if left untrimmed, so consider how much ground space that is going to take up. Depending on your particular situation you could trim up the lower several feet, as they grow, creating trunks on your screen, which will free up ground-level space, but even then you should plant 6 feet or more from your property line, so that the trees are actually ‘yours’ completely.

For many medium to large-sized gardens, that kind of space is not an issue, but in a smaller garden you might want to consider something smaller, such as Emerald Green Arborvitae, which only grows to about 12 feet tall. It is hardy all the way from zone 2 to zone 7, making it the perfect choice for a smaller screen in colder areas.

How Fast Will They Grow?

Here we get into the reason for the enormous popularity of Thuja Green Giant – its growth rate. Young plants can add 3 feet a year – and even more sometimes. As they mature the growth does slow down, but still exceeds a foot a year. This can be seen with the original planting, where a plant at the National Arboretum in Washington reached 30 feet in 25 years. Tiny plants have been proven in trials to reach 10 feet in 7 years, faster than any other evergreen around.

Good soil preparation and a regular fertilizer program will give your plants the best start and the quickest growth rate, so go that extra distance and reap the rewards.

How Far Apart should I Plant?

Given how big Thuja Green Giant gets, you don’t need a lot of plants to make a screen. Depending on how quickly you want that screen to develop fully, you should plant 5 feet apart for a quick screen, and as much as 10 feet apart for something less solid, that will give the effect of screening without making a solid wall of green. If you do want solid, and you have enough room, then plant a double row. Allow 5 feet between the rows, and plant 8 feet apart in each row for a quicker screen, or up to 12 feet apart for something looser. Stagger the planting in each row, so that one plant stands in the middle of the gap in the other row, creating a tight zig-zag.

What About After-care?

Since Thuja Green Giant is not eaten by deer – at least not usually – and has no significant pests or diseases, there is nothing to do in that direction. The most important care is watering during the first growing season, which should be once a week. Don’t rely on showers or thunderstorms, as most of that water only wets the top inch or two in summer. Instead go for a deep soak from a gently-running hose on each plant, or by installing trickle pipe along the line. It’s important to keep the soil further away from each tree moist too, because you want to encourage the roots to grow outwards into a large volume of soil. That will happen much more if the ground around is temptingly moist, rather than dry.

After that vital first year you don’t need to give so much attention to your trees. Watch for dry periods in the second and third years and give those deep soaks again if the soil is dry below the top few inches. A quick dig around with a spade will show you that – just turn up a few inches of soil and feel for moisture. Increased watering during the early years will also accelerate growth, especially if combined with a fertilizer program.

In the early years liquid fertilizer is best – it gets straight to the roots and is taken up quickly. Feed each month for the best results, and that can be a little time-consuming, so after two or three years switch to slow-release granular fertilizers that only need one application a year, in spring. Choose a blend suitable for evergreens and look for Iron and Magnesium in the added micronutrients listed on the label. They will keep your screen a rich green color all year round.

Should I Trim?

Thuja Green Giant produces a dense plant without trimming, but as the early growth is fast and so more open, a light trim each year while the plants are small enough to reach will make it thicker much more quickly. You only need to take off an inch or two, so it has no real effect on the size or rate of growth, but it certainly makes for a dense screen early on.


Thuja Green Giant is the number one choice across much of the country, and it is probably the best choice for you too, but it pays to think it through first. Hopefully these notes will help you reach the right decision.