Ailanthus altissima Seeds | Tree of Heaven
LATIN NAME: Ailanthus altissima
COMMON NAME: Tree of Heaven
Plant Profile
The leaf is the giveaway long before the tree is big enough to matter. Ailanthus carries huge pinnately compound leaves, sometimes half a metre long, each one split into a dozen or more leaflets with a single large gland, or sometimes two, stamped on the underside at the base of the blade. Crush a leaflet and the smell is sharp, almost rancid, which is why the plant is also called stinking sumac. That gland and that scent are the fastest field mark in the genus, and they warn you what you are dealing with.
The tree grows with a speed that alarms neighbours, and the trunk lifts into a broad, open crown of coarse branches. In its first years it can outpace almost anything planted near it, which is the root of both its fame and its bad name.
The trees are mostly separate sexed, male and female on different plants, and only the female sets the showy winged fruit. The male flowers release a heavy scent that is sweet yet unpleasant in early summer that some people find hard to live near, while the female carries clusters of flat, reddish-brown samaras that spin down in the wind. If you want the tree without the smell, you must choose a male clone, because a seedling female will fruit and a seedling male will stink.
Beyond ailanthone the bark and root hold a set of quassinoids and tannins, the basis of the traditional drug Chun Pi used in Chinese medicine for bowel complaints. The bark is bitter to the point of unpleasant, which is the quassinoid signature, and the same bitterness deters most grazing animals. Handle the bark and root with respect and keep them away from children and pets.
The tree’s tolerance of poor, compacted, and even contaminated ground has pushed it into biotech as a biomass and phytoremediation candidate. It grows on mine spoil and roadside fill where little else will, and its fast wood makes a low-grade fuel and pulp. Researchers weigh that service against its invasive spread, and the honest answer is that the tree is useful precisely where you can also control it.
Science & Biotechnology
The reason Ailanthus smothers its neighbours is chemical. The root and leaf release ailanthone, a quassinoid that slows the growth of other plants around it, a process called allelopathy. This is one of the best-documented cases in a street tree, and it is why a bed beneath an Ailanthus stays bare while the tree itself thrives. The compound is also studied for activity against insects and fungi, which is the other side of the same chemistry.
In the herb shop the dried bark is a recognised item with a long record, prepared by stripping and drying the outer layer. It is a bitter tonic, not a casual tea, and it should be sourced as a finished product rather than gathered from a roadside tree. The line between a useful bark and a weed is the same plant seen two ways.
As an ornamental the tree earns points for toughness: it stands heat, drought, and city smoke, and it fills a bare lot in a single season. The cost is control, because the root suckers freely and the seed travels, so a planted tree becomes a thicket if left alone. Choose the site as if the tree will outlive you, because it might.
The practical warning is simple. Wear gloves when cutting, bag the suckers, and never plant it where a natural area is nearby. The sap can irritate skin, and the seedlings appear in borders where you did not put them. A gardener who respects the chemistry will use the tree; one who ignores it will be overrun.
Uses & Benefits
Native to the warm valleys of central China, Ailanthus was sent to Europe and America in the eighteenth century as a fast ornamental and a street tree for poor ground. It took to the rubble of industrial cities so well that it became the emblem of the tenement yard and the subject of a famous novel. In China the same tree was always also a medicine and a timber, never just a weed.
Growing from Seed
The samara is a winged seed that loses viability once it dries, so sow it as soon as it falls into a moist, open tray. Lay it on the surface and press lightly, then keep it cool and damp through the cold months so the embryo develops. Fresh seed rises well; stored seed often fails, which is the trap for the beginner.
A young tree throws suckers from the root that crowd the base, and these must be cut at the point they leave the root, not just snapped at the soil. Thin to a single clean stem if you want a tree, or let a clump form if you want a screen. Decide early, because the suckers harden fast.
Root barrier buried around the planting keeps the suckers in check and protects nearby beds. A tree in a confined pit, against hard ground, is far easier to live with than a free root in open soil. Mow or cut the volunteer seedlings the moment they appear so the patch stays yours.
Our Take
I treat Ailanthus as a controlled subject, not a pet, and I respect the bark more than the look. For related trees of warm valleys, the Chinese mahogany, the chinaberry, the staghorn sumac, and the osage orange all share the tough-tree temperament. Plant with a barrier and a plan, and the tree of heaven stays a tree, not a takeover.
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