- Type
- Trees & Vines
- Difficulty
- Moderate
- Season
- Spring·Summer
- Sowing
- Plant a sapling
Silk tree
Albizia julibrissin
Saponin glycosides and flavonoids · the garden tree that folds its leaves at dusk
The silk tree is a legume planted in yards, parks and along streets. In summer pink blooms open at every branch tip like unwound skeins of thread — what looks like petals is a fan of long stamens. The leaves are finely divided compound leaves, and at sundown the paired leaflets fold together. What the Donguibogam lists in the Tree section as 合歡皮 is the bark of this tree, and it records the alternative names 合昏 and 夜合皮, both from the way the leaves close at evening. The text describes the tree as resembling a paulownia with very supple branches, and the leaves as like those of honey locust or pagoda tree, extremely fine and dense and interlocking with one another. It says yellowish-white flowers open in the fifth month by the lunar calendar with the upper part of the petals like floss, that pods form in autumn, and that the seeds are very thin and small. Bark and leaf, it adds, were gathered without regard to season. Today the summer flowers are dried for a flower tea, while the bark circulates as the material called hapwanpi.
Year-Round Calendar
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Where It Grows
- Main producer This is the centre for harvesting the flowers and the stem bark known as haphwanpi (silk tree bark). The growing regions are Central China, North China, Sichuan and Hubei.
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Major producer
It grows wild on hill slopes and around villages in the central region and southward, and is also widely planted as a street tree and a garden tree. Harvest June, July
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- Wild population It grows wild from Honshu southward under the name nemunoki.
- Wild population The forests on the southern shore of the Caspian Sea are the western edge of this tree's range.
It is native to temperate and subtropical Asia, from the Caspian coast of Iran through China, the Korean Peninsula and Japan, so it cannot be pinned to any one country. China is the centre of the harvest for the flowers and the stem bark. In the southeastern United States and southern Europe the tree arrived as an ornamental and then spread on its own, and is treated there as an invasive species, so those areas have not been counted as growing regions.
- Optimum
- 20~30℃
- Range
- 10~35℃
- Hardiness
- Half-hardy
A deciduous tree that likes summer heat and sun and stands up well to drought. Its tolerance of winter cold has limits, so in Korea it is planted mainly in the central region and southward, and in cold years the branch tips freeze. This tree has a habit of leafing out late in spring, not breaking bud until May, so until then it looks dead.
Harvested 3–5 years after planting. Three or four to five years must pass after a sapling is planted before it flowers properly. The month of planting and the month of harvesting the flowers do not fall in the same year.
In Korea Central Korea and south
It is common on hill slopes, along the coast and at the entrances to villages in the central region and southward. In the mountains of Gangwon and the northern inland areas the branches freeze in winter and the tree cannot grow large.
How to grow
- Light
- An open spot in full sun. In shade the flowering thins out
- Soil and depth
- Not fussy given drainage. Dig the hole twice the width of the root ball and backfill with loose soil
- Spacing
- Grown out, the branches spread sideways like an umbrella. Set it at least 4m from buildings and walls
- Watering
- Watch it through the first summer only. Once established it largely carries itself on rainfall
- Feeding
- Work compost shallowly around the base in late autumn after leaf fall. Heavy nitrogen runs the branches long and cuts the flowering
- Harvest
- Pick the flowers in June or July, on a day they open fully, once the dew has dried. Spread them in the shade to dry right away
What makes the difference. Dried flowers crumble easily, so keep them sealed somewhere cool and dark. Once they take up damp, the aroma is the first thing to go
Why this one is harder. Branches snap readily and small wood drops constantly, which makes for yard work. It also seeds freely, so young trees come up around it; cut the pods before they ripen if that is unwanted
Common problems
- Aphids You will see Colonies on the young branch tips, leaves turning sticky What to do Wash them off with a jet of water; if it recurs, use an egg-yolk oil spray. Observe spray intervals where flowers are to be picked
- Albizia psyllid You will see Small insects on the leaf undersides, with sticky honeydew dropping so the leaves below look sooty What to do Spray water so it reaches the leaf undersides, and cut out badly affected branches
- Wilt You will see In midsummer the leaves of one branch wilt suddenly and dry while still hanging What to do Avoid spots where water sits and cut damaged branches away. Disinfect the tools and do not replant the same species there
This page describes how a crop is grown and used. It does not claim health effects for any food, nor is it intended to prevent or treat disease. Component and study notes are references only and do not mean the same result occurs in people. Consult a medical professional about health concerns.
Health Benefits
The old record — hapwanpi (合歡皮). The Donguibogam lists it in the Tree section as 合歡皮, meaning the stem bark of the silk tree. It sets the nature down as neutral, the taste as sweet, and free of toxicity. The tree resembles a paulownia with very supple branches, it says, and the leaves are like those of honey locust or pagoda tree, extremely fine and dense and interlocking. Because the leaves close at evening it also carried the names 合昏 and 夜合皮. Yellowish-white flowers open in the fifth month by the lunar calendar with the upper part of the petals like floss, pods set in autumn, and the seeds are very thin and small. Bark and leaf were gathered without regard to season. What an old medical text wrote differs from how it is judged today.
Saponin glycosides in the genus Albizia. Triterpene saponin glycosides have been isolated from the stem bark of Albizia species in repeated analyses. The froth that rises when the bark is simmered is discussed alongside the same compounds. These are compositional analyses and have nothing to do with preventing or treating disease.
Nyctinasty — the folding of the leaves. At sundown the paired leaflets of the silk tree fold together. This is nyctinasty, widely observed in the pea family, and is explained by cells at the base of the leaf stalk moving water between them. The old names 合昏 and 夜合 came from that movement. This is a record of the plant's behaviour.
Nutrition
- Saponin glycosides (distributed in the stem bark) — triterpene glycosides reported across the genus Albizia
- Flavonoids (distributed in flower and leaf) — phenolic compounds common in plants
- Tannins (distributed in the stem bark) — polyphenols behind the astringency
- Aroma compounds (given off by the flowers) — the volatiles behind the faint sweetness of the flower tea
Steeped as a flower tea Silk tree flower tea is dried blossom steeped in hot water. The aroma is faint and the taste mild, and even a long steep adds little bitterness. The flowers break up easily, so steep them in a strainer.
Saponin glycosides in the bark Analyses report triterpene saponin glycosides isolated from the stem bark of Albizia species. The froth that rises when bark is simmered is discussed alongside them. This entry stays with the compositional record.
Flavonoids in flower and leaf Flavonoid phenolics are found in the flowers and leaves. They are a compound group widespread among plants, and the pale colour of the tea comes from them. This is what compositional analysis shows and nothing beyond it.
Which parts are used and which are not What is treated as food on this tree is the flower; the bark circulates as a medicinal material. The flat pods that set in autumn and the seeds inside them are not eaten. Parts of this tree serve different purposes, and belonging to one tree does not put them in one category.
Pairings
○ Hot water — the flower tea — Steep a pinch of dried flowers for three or four minutes in water around 90 degrees. The aroma is faint, and water cooled too far yields nothing at all. A second steep still gives a cup.
○ Jujube and honey — A touch of sweetness sharpens the faint floral note rather than covering it. Add honey after pouring, once the cup has cooled a little. Jujube
○ Morning flowers once the dew has dried — Pick flowers for tea on a day they open fully, after the dew has gone. Dried while wet they blacken. Spread them in the shade right where you picked them and the pink holds.
△ Seeds and pods — The flat pods that set in autumn and the seeds inside are not treated as food. They look like beans and are easy for a child to pick up, so clear fallen pods away. Do not roast or boil the seeds to eat.
△ Picking from street and park trees — Trees along roads and in parks get sprayed for pests and take traffic exhaust straight onto their surfaces. Pick flowers for tea from a tree in your own yard or plot. Nor should flowers or bark be taken from someone else's tree.
△ Stripping bark yourself — Bark taken in a ring around the trunk cuts the tree's water route and kills it. Buy hapwanpi as a traded material rather than stripping the bark from a living garden tree.
△ On medication or pregnant — Hapwanpi has long been handled as a medicinal material. Anyone on medication, pregnant or nursing should not simmer the bark and drink it. Fix a number of cups a day for the flower tea as well.
Varieties
- Silk tree (sapling) — The familiar garden tree. Pink stamens spread like unwound thread
- Albizia kalkora (sapling) — Larger leaves than the silk tree and flowers closer to white. It grows on the southern coast
- Aeschynomene indica (wild) — An annual herb with a similar Korean name, not a tree at all. It grows on paddy banks and at the water's edge
- Hapwanpi (stem bark) (dried) — The dried stem bark of the silk tree. This is the name it carries in the market
- Hapwanhwa (flowers) (dried) — Summer flowers dried. Steeped as a flower tea
Source: Donguibogam, Tree Section 合歡皮 · Korea National Arboretum species information system