Thuja Green Giant - Growing and Care Guide

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by Max - last update on October 21, 2020, 8:55 am
Thuja Green Giant Care Guide

This evergreen coniferous tree is a hybrid that resulted from crossing two kinds of Thuja trees. These are the western red cedar (Thuja plicata), which is native to the northwestern United States, and the Japanese thuja (Thuja standishii), which is native to several Japanese islands. The Thuja Green Giant is believed to have been created in Denmark in the 1960s, and a single plant was given to the US in 1967; from that, more of the same plant was propagated and planted throughout the east of the country. This is now an enormously popular plant, which thrives in cool conditions, is easy to grow, and has an attractive architectural look.

The Thuja Green Giant is one of the fastest growing trees of its size. If you want to create a privacy screen or hedge in your garden in a relatively short space of time, then this is the tree to select, as it can grow in height by between three and five feet each year. The eventual height of the tree is typically between 40 and 60 feet, so you'll need to ensure you have plenty of growing room to accommodate it.

When young, the tree has a narrow conical habit, which develops into a slightly broader pyramid shape once mature. As an evergreen, this tree retains its glorious deep green foliage all year round, providing life and color in the garden when deciduous trees are bare. The foliage is dense and sprays out in flattened fan shapes. The leaves are tiny and scale-like, in a glossy shade of green that becomes darker during fall and winter. The foliage of the tree overlaps each other heavily to give the tree an almost solid look. This dense nature of the tree makes it an ideal place for small birds and other wildlife to take shelter, especially as it retains its thick foliage during the colder winter months. The tree also produces seeds, which provide an important source of food to wild animals.

Thuja Green Giants can be planted closely together in rows to form hedges, or they also look very striking when planted in rows with several feet of empty space between each one. Their striking visual appeal also means they work well as individual specimen plants. These are low maintenance trees that continue to look magnificent with hardly any effort at all. They rarely suffer from pest problems and grow easily in a wide variety of conditions. They also have the benefit of being more resistant to deer than most other sorts of Thuja trees. As an added bonus, they emit a pleasant scent when the foliage is crushed.

Thuja Green Giant Overview

Quick Facts

OriginHybrid
FamilyCupressaceae
Scientific NameThuja standishii x plicata
USDAHardiness Zones: 5-8
TypeEvergreen conifer tree
Common NamesGreen Giant Arborvitae. Thuja Green Giant
HeightUp to 60 feet tall
LightFull sun
WateringAverage moisture needs
ToxicityMildly toxic to pets
PestsMostly disease-free, look out for scale and aphids

Watering

Thuja Green Giants need plenty of water when they are young, though they will not survive in wet soil, so take care to ensure the soil does not become waterlogged. As the plant matures, it will usually cope well with just rainwater alone, though it doesn't tolerate dry conditions, so you might need to supplement water if you go through any long periods of drought. Though this tree can survive on rainwater, it will thrive when kept in continually moist conditions. This is a fast-growing tree that can grow anywhere from three to five feet in a single growing season, but if you want optimum growth, then you will need to keep the roots in moist soil.

Soil

Thuja Green Giant trees tolerate a wide range of soil types, making them suitable for planting even in clay soils that many plants cannot thrive in. This tree will adapt to acidic, alkaline, or neutral soils with ease and can grow well in both heavy clay soils or light and sandy soils. You don't need to worry about amending poor soils before planting this tree because it will find a way to thrive no matter what soil type it is grown in.

However, if you want to provide the tree with the best chance of performing well, then it prefers a loamy and fertile soil that is kept consistently moist. Deep soils are also beneficial for this tree to allow the roots to spread far and wide. Ideally, the soil that a Thuja Green Giant is grown in should be well-draining in order to avoid the soil becoming waterlogged, which can lead to root rot. This tree does not fare well in wet soils, so if your soil does not drain well and water pools on top of it, then you may wish to add sand and some organic compost in to improve drainage.  It is a good idea to add a few inches of mulch over the top of the soil around the base of the tree, as this will help to retain moisture by reducing water evaporation, and it will also regulate the temperature of the soil as a means of insulation.

The shallow roots of the tree can become damaged in very low or high temperatures, and the mulch will help to prevent this damage by ensuring the soil remains cool in the summer and warm in the winter.

Light

Light

This tree thrives in full sun and requires a minimum of four hours of direct sun each day. It is not a fan of high temperatures, and so during hot summer afternoons, it will appreciate some relief from the heat in the form of shade. If you live in a cool climate, then you can situate your tree in a position where it remains in full sun all day long, but warm summer climates would be better off growing this tree in partial shade.

When a plant needs some shade during the summer, you should always aim to provide this shade during the afternoon, as this is when the sun is at its most intense, and scorching is more likely to happen. The morning sun is weaker, and temperatures are typically several degrees lower in the morning, and therefore this type of direct sun is much better tolerated by plants that are sensitive to heat.

Temperature

Temperature

This tree is suitable for growing in USDA hardiness zones 5-8. It thrives in eastern North America, where the climate is fairly stable, not getting too hot in the summer and also not too cold in the winter. The tree is sensitive to extreme temperatures on either end of the scale and may need to be protected from extreme weather in some instances. If you are on the colder end of the appropriate hardiness zones, then you should certainly mulch the soil around your Thuja Green Giant to ensure its roots do not freeze during winter. You may also want to ensure the tree is planted in a sheltered position to avoid it from being subjected to cold winds and heavy rain or snow.

Once the tree is mature, it can withstand these types of weather conditions and therefore makes a good windbreak, but when young, you may need to protect the tree with horticultural blankets. If you are towards the higher end of the advised hardiness zones, then you will need to give your tree a few hours of shade each afternoon in the summer to prevent it from getting too hot. You should also take care to provide extra water to this tree if it is in a hot summer climate because the soil can dry out more quickly, and it will not tolerate dry conditions.

Propagation

Thuja Green Giant trees can be propagated from cuttings. The best time to take a cutting is during spring or early summer when the tree is in active growth, as this means the cutting will develop roots more quickly. Take a cutting of around six inches in length, being careful to ensure you choose a branch that is semi-hardwood. This means your cutting should be taken from a part of the tree that is neither very old nor very new. The cutting should not be very flexible, as this indicates that it is new growth. It should also not be too rigid as this indicates old growth.

Semi-hardwood will have some flexibility but also offer a good amount of resistance. After making the cutting, remove all of the lower stems and leaves so that you have a single-stemmed cutting. Prepare a pot of moist potting soil, dip the raw end of the cutting into rooting hormone powder, and plant it in the soil. It should be firmly tucked in so that it stands upright. You then need to place the pot in a bright window and ensure the soil is kept moist but not wet. To speed up the rooting process, you can mist the cutting to increase humidity or place a clear plastic bag over it to replicate greenhouse conditions.

Rooting time can vary from a few weeks to a few months. To check if the cutting has rooted, you can tug it upwards from the soil. If it easily slides out, then roots have not yet formed, but if it offers resistance, then roots are holding the cutting down into the soil. Allow the cutting to develop for several more weeks after roots have sprouted to ensure it gains strength, and then transplant it to a larger pot or directly into the ground outside.

Repotting

If you have propagated the Thuja Green Giant yourself, or if you have bought it as a small plant from a nursery, then you will have a potted plant you need to transplant to the ground outside. Because of the sheer size of this tree, you shouldn't try to grow it in a container. It will perform much better when grown directly in the ground and will be much easier for you to care for. Imagine trying to repot a tree that is 40 feet tall!

Fortunately, these trees transplant easily, so even if you have kept this tree in a pot for several years, you can be safe in the knowledge that it will continue to thrive after it is moved to a more permanent spot in the ground. When removing this tree from its pot, you should gently tug at the main part of the tree while twisting the pot to ease out the roots and the soil.

Once removed, crumble the soil with your fingers and gently encourage the roots to separate; this will help the roots spread out underground and allow the tree to establish itself more quickly after being transplanted. Dig a large, wide hole for your tree, a little bigger than the root ball, and backfill it with new compost. Position the tree in its new hole, and surround the root ball with more fresh compost, and firmly tuck it in. The base of the trunk should sit at the same level in the ground soil as it sat in the potted soil. Water the soil generously to help the tree settle in.

Pruning

This is a tree that does not require any pruning at all, as it forms a neat column shape when young, developing to a wider pyramid shape with age. The only exception to this is if you are growing the tree as a hedge; in that case, it will need pruning to form a uniform screen. It should be pruned in early spring but also tolerate early summer pruning. Be careful not to cut the tree back too heavily because underneath the new outer growth will be bare, old branches. New growth will not happen on these older branches, so if you prune the tree back too far, you will have permanent bare gaps in your hedge. Like with any plant, always prune away any damaged, diseased, or dead branches when they appear.

Thuja Green Giant - Growing and Care Guide

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