Tree of heaven (Ailanthus altissima) is a fast-growing tree that is banned from sale in the UK. Originally introduced from China in the 18th century, tree of heaven proved to be extremely tolerant of atmospheric pollution and was widely planted, but its speedy growth, fast reproduction, suckering habit and toxicity to nearby plants, has resulted in its classification as an invasive non-native species in accordance with Schedule 9 of the Wildlife & Countryside Act.
What is tree of heaven?
Tree of heaven is a deciduous, large, and fast-growing tree. It forms a spreading crown of branches and readily produces suckers from the roots. Tree of heaven tolerates drought, full sun and poor soils, and sometimes even grows in paving cracks. Contact with tree of heaven growth can cause skin irritation to people and pets.
Identifying tree of heaven
Tree of heaven grows to an eventual height of 20-30m. It has large, pinnate leaves around 60cm long, although on young trees the leaves can grow up to 1m long. Young leaves are reddish green, maturing to green, and give off an unpleasant odour when crushed. Tree of heaven is dicoceous, meaning the trees are either male or female. Female tree of heaven flower clusters are small and green in colour, and are followed by reddish, winged or key-like fruit, known as samaras. Male flowers are similar in appearance to female flowers but appear in greater numbers, and then wither away rather than develop fruit. The flowers of male trees have an unpleasant smell, said to be reminiscent of skunks.
Tree of heaven identification can be tricky – it can easily be confused with staghorn sumac, which has similar leaves but reddish rather than green flowers, and ash trees, which also have large pinnate green leaves but which don’t release a bad smell when crushed.
Does tree of heaven cause problems?
The fast growth and suckering habit of tree of heaven means it is a problem tree, as it can quickly spread and out-compete native plants. Other problems include the dangers of skin irritation to people and pets, and its pollen, which can cause allergic reactions in some people.
Tree of heaven and the law
Tree of heaven is classed as an invasive, non-native species under Schedule 9 of the UK Wildlife & Countryside Act. This means it’s banned from sale, and it’s an offence to plant or allow tree of heaven to spread into the wild. By law, any tree of heaven tree growing in a garden should be controlled and prevented from spreading into wild areas.
How to prevent tree of heaven
Pull up tree of heaven seedlings when young, before the deep tap root develops.
How to control tree of heaven
Regular cutting back restricts the growth of tree of heaven. If done annually, tree of heaven can be kept as a non-flowering shrub with large, attractive leaves. Cutting back, even to ground level, does not kill tree of heaven alone, unless herbicide is applied to the freshly cut stems. This is best done by professional contractors.
How to remove tree of heaven
After a mature tree of heaven has been cut down, the roots need to be removed or regrowth quickly occurs. Excavating the roots usually requires a mechanical digger. Using a powered stump grinder to remove the stump may not be sufficient to get rid of tree of heaven, because suckers are often produced from the roots and can appear many metres away.
Frequently asked questions
Is tree of heaven invasive in the UK?
Yes, tree of heaven is classed as an invasive non-native species under Schedule 9 of the UK Wildlife & Countryside Act.
Is tree of heaven poisonous to other plants?
Tree of heaven is allelopathic, which means it gives off a chemical that inhibits the growth of other plants, but does not necessarily kill them.
