Topic: tree of life, Thuja
The tree of life (Thuja) is also called in German mostly with its botanical generic name Thuja and is especially popular as a hedge plant. However, thuja hedges are planted less and less today, because they – like the washed concrete slabs that were very common at that time – have the dusty flair of the 70s. Nevertheless, thuja hedges have their advantages, because they are extremely frost hardy and windproof. In addition, they grow rapidly, are inexpensive and as evergreens absolutely opaque all year round.
the type Thuja consists of altogether only six types, that are widespread partially in North America, partially in East-Asia. The two New World species that are most in demand as garden shrubs are the western tree of life (Thuja occidentalis) and the giant tree of life (Thuja plicata). More popular plants are the Oriental Tree of Life (Thuja orientalis), which is common in China and Manchuria, and the Japanese Tree of Life (Thuja standishii). The main reason for their lower distribution in our gardens is that they are not as frost hardy as their North American relatives. The plant genus Thuja belongs botanically to the cypress family (Cupressaceae). As such the different Thuja-Arten show also the typical, closely at the branches lying scale sheets.
In the garden, the evergreen hedge plant is usually found as the western tree of life. It grows naturally in north-eastern America and in Canada in the so-called boreal coniferous forests, which in places extend as far as the Arctic Circle. Growing freely it reaches a height of 20 meters and more. The trees can live for about 180 years and reach a trunk diameter of almost two metres. The western tree of life has a densely branched, conical crown and arching branches. The bark is orange-brown and longitudinally cracked, the scaleshaped leaves sit flat against the shoots and are dull green on the upper side and often olive green in winter. The shoots and leaves spread a very aromatic scent when rubbed. The tree of life is monoecious, i.e. it carries male and female flowers on one plant, but separately from each other. The male cones are only about two millimetres large and reddish, the female cones are light green at first, later light brown and up to eight millimetres long, they have a conical shape and stand at the shoot tips. The mature cones open and release winged seeds.
There are a number of varieties of the western tree of life for the garden, which differ in different leaf colours and different growth forms. They are all more compact in growth than the game species and more suitable for the garden. The giant tree of life is larger and grew stronger than the western tree of life. It is widespread in Pacific North America from Northern California to Southern Alaska and can reach heights of over 60 metres. It is also very suitable as a hedge, but tends to need to be pruned a little more frequently. In North America it is particularly important as a forest tree. The red and very light wood smells aromatic and is slightly sensitive to pressure. Under the name “Red Cedar” it is also offered here in the building materials trade.
Trees of life grow best in full sunny locations, but also tolerate light shadows. It is important that the soil is moist and does not dry out even in summer. The best place to keep awake is on limy, sandy loamy soils. However, the woody plants can adapt very well to different soil types and pH values and, with a good supply of humus and soil moisture, also grow on acid sandy soils.
Trees of life are popular as fast-growing, evergreen hedges. Thuja hedges grow very densely and offer excellent privacy and wind protection. Since the wild species are very vigorous, it is better to use the somewhat more filigree, narrow-growing varieties ‘Emerald’ or ‘Holmstrup’ for hedges. Some small, cushion-like or spherically growing varieties are also suitable for stone or heather gardens and for grave gardening, provided that the soil here does not dry out too much in summer. The narrow column-shaped trees of life are also often planted in gardens with a Mediterranean character as a substitute for the real cypress (Cupressus sempervirens), which is not hardy in our country. Since trees of life tolerate frequent pruning well, they can also be cultivated as spherically or pyramid-shaped cut shrubs. They can also let the wild species of the trees of life in the garden grow freely as solitary shrubs: over the decades they lose their “cemetery character” and show increasingly loose growth as they age. Old trees have a picturesque bark with longitudinal cracks and a beautiful pyramidal crown.
Thuja hedges must be cut regularly to ensure that they remain dense and grow compactly. Avoid a stronger cut into the unscaled shoot areas, as the plants will then only sprout sparsely again. Stronger rejuvenation cuts into the old parts of the branches cause the plants to remain bare. Therefore, it is very difficult to get an old thuja hedge back into shape if it has not been cut for a few years. Strong growing thuja hedges need two cuts per year: the first one towards the end of June and another one at the end of August. Even skin contact with the shoots can lead to redness and itching in sensitive people. When consumed, mucous membrane irritations and gastrointestinal complaints can occur. The cause of the poisoning symptoms is a monoterpene called thujon.
Most attention must be paid to the otherwise rather undemanding trees of life after planting. During the first three years you should make sure that the plants get enough moisture. This is all the more important the larger and older the trees of life are during planting. Later, the plants are rooted in so well that they can also get moisture from deeper soil layers. Mulching, for example with lawn cuttings, helps to prevent the soil from drying out in spring and summer. With two prunings per year, a compost fertilisation of about two litres per square metre is also recommended in spring. Humus also improves the soil structure and water storage capacity of the earth.
The wild species of the tree of life can be reproduced by sowing in autumn. The seeds need a cold stimulus to germinate. The many thuja varieties are best propagated by cutting mature shoots in late summer. So-called cracklings are used for propagation: these are one- to two-year-old side shoots that are torn off from the main shoot. Cut the remaining strip of bark with a sharp knife, remove the lower side shoots and put the shoots into the cultivated soil. The rooting under a transparent cover is very reliable at ground temperatures above 20 degrees, but can take up to eight weeks.
Diseases and pests
The tree of life is not always sick when it gets brown leaves. In winter, the colouring of the foliage of wild species and some varieties usually changes to a brownish colour. This serves as frost protection and can occur more strongly in very cold winters. Leaves and shoots can also turn brown during prolonged drought and road salt damage. Some fungal diseases can lead to needle tan. One usually finds dark brown to black spore-bearings depending on the pathogen on the dead shoots. Other fungal diseases attack the roots, especially in stagnant locations, with the result that the entire plant often dies. The Thuja miner moth can be found on the plants of pests. Occasionally it comes also to the infestation with tree and sign lice.
Whether potted plants such as oleanders or indoor plants such as orchids: The scale insect infests the most diverse plants. René Wadas, a herbalist, will give you his tips on pest prevention and control: Production: Folkert Siemens; Camera: Fabian Primsch; Editing: Dennis Fuhro; Photo: Flora Press/Thomas Lohrer
Thuja in the MY BEAUTIFUL GARDEN-Shop
I am Don Burke, one of the authors at My Garden Guide. I am a horticulturist that cultivates, grows, and cares for plants, ranging from shrubs and fruits to flowers. I do it in my own garden and in my nursery. I show you how to take care of your garden and how to perform garden landscaping in an easy way, step by step.I am originally from Sydney and I wrote in local magazines. Later on, I have decided, more than two decades ago, to create my own blog. My area of specialization is related to orchid care, succulent care, and the study of the substrate and the soil. Therefore, you will see many articles dedicated to these disciplines. I also provide advice about how to improve the landscape design of your garden.