- Type
- Trees & Vines
- Difficulty
- Hard
- Season
- Summer
- Sowing
- Plant a sapling
Japanese Pagoda Tree
Styphnolobium japonicum
Rutin · the flower buds of a village landmark tree
The Japanese pagoda tree is a large legume tree planted at village entrances and in old palace courtyards. In summer pale yellow flowers mass at every branch tip, and the ground beneath turns yellow with them. Those flowers and the buds that have not yet opened, dried, are sold in herb markets as goehwa (槐花) and goemi (槐米) and steeped as tea. The buds are known as a rutin-rich material and serve as an industrial source for extracting it. The flowers dye a strong yellow and have long been used as a natural dyestuff. The Donguibogam lists the flower in its Wood section as goehwa (槐花), also called goea (槐鵝), and records that it is lightly roasted before use. It is a short entry quoting the Bencao, so no description of nature or taste is attached here. To get the flowers, buying them dried at a herb market beats picking from a street tree.
Year-Round Calendar
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Where It Grows
- Origin Native to the mountains of north China, with flower buds (huaimi) harvested in bulk in Shanxi, Henan and Hebei. Most of the world's raw material for rutin comes from here.
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Major producer
Long planted at village entrances, in palace courtyards and along streets, with the flower buds gathered in summer. Harvest July, August
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- Major producer Despite the japonicum in its botanical name, in Japan too the tree was brought in and planted. It is grown as a street and garden tree, and the flowers are harvested.
Its botanical name is Styphnolobium japonicum, but it is native not to Japan but to north China; in Korea and Japan it was brought in and planted. It has now spread widely as a street tree in European and North American cities as well, yet production of the harvested flower buds is still heavily concentrated in China.
- Optimum
- 18~28℃
- Range
- 8~35℃
- Hardiness
- Hardy
Flowering is heaviest in open ground that gets sun all day. The tree tolerates heat, drought and urban exhaust fumes well, and comes through winters of around −20℃. It is not fussy about soil, but its roots run deep and spread wide, so allow plenty of room where you plant it.
Harvested 8–15 years after planting. It takes roughly eight to fifteen years after planting before the tree flowers in any quantity. The July–August flower bud harvest comes only once the tree is well established.
In Korea Nationwide
Planted throughout the country. Old specimens survive at village entrances and in the courtyards of former palaces, and it is also used as a street tree.
How to grow
- Light
- An open position in full sun all day. In shade it flowers sparsely
- Soil and depth
- Free-draining soil at least 50cm deep. It is not particular about soil and tolerates dry ground
- Spacing
- At maturity it spreads wide in height and width alike. Plant one tree only, well clear of buildings and walls
- Watering
- Keep it from drying out through the first year only. Once established it carries itself on rainfall
- Feeding
- Work compost around the base after leaf fall. It grows well without heavy feeding
- Harvest
- July and August. Pick on a morning after the dew has dried, when the buds have swelled but not opened. Fully opened flowers are not taken as material
What makes the difference. Dry the picked buds spread in a breezy shaded spot. Direct sun fades them; once fully dry, seal them in a container and keep them somewhere cool
Why this one is harder. It grows too large for a small yard. Within a few years it reaches the roof and the wires, and in summer the flowers drop all at once and make the ground slippery. Allow generously for the position at planting
Common problems
- Aphids You will see New shoot tips turn sticky and the leaves and ground beneath go glossy What to do Wash them off with a jet of water. Do not spray a tree you intend to pick flowers from
- Pagoda tree rust You will see Swollen gall-like patches on leaves and young branches, and early leaf fall What to do Cut out affected branches and bag them for disposal. Rake up and remove fallen leaves to cut next year's inoculum
- Leaf-eating caterpillars You will see Leaves rolled or grazed from the margin in summer What to do With few of them, pick them off by hand. A large tree generally recovers on its own
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
What the Donguibogam records — goehwa (槐花). The Donguibogam lists the flower in its Wood section as goehwa (槐花), also called goea (槐鵝). It records the preparation: lightly roasted before use. The entry is short and quotes the Bencao, so no description of nature or taste is attached here. This is a historical medical record and differs from modern medical judgment.
Buds and rutin. That pagoda tree buds are rich in rutin and serve as a source for extracting it has long been addressed in food and chemical science. Measurements also report that levels fall once the buds open. These are compositional analyses and have nothing to do with preventing or treating disease.
Nutrition
- Rutin (abundant in the flower buds) — the flavonoid glycoside extracted from pagoda tree buds
- Quercetin (what remains when rutin breaks down) — the flavonoid backbone of rutin
- Yellow pigment (in the flowers and buds) — the flower colour once used as a natural dye
Buds and rutin The unopened flower buds of the pagoda tree are known as a rutin-rich material and are used as an industrial source for extracting it. Levels fall once the flowers open fully, which is why they are picked in bud. This entry stays with the compositional record.
How it is steeped Dried flowers and buds are steeped in hot water. A long boil brings the astringency forward, so keep the steep short. The old text records light roasting before use, and what herb markets sell today is usually roasted and dried.
The yellow dye The flowers dye a strong yellow and have long been used as a natural dyestuff. The steeped liquid stains cloth and crockery, so do not leave it standing in a white cup.
Pairings
○ Dried jujube — On its own the tea leads with astringency, so dried jujube often goes into the pot with it. A little sweetness makes it easier to drink. Jujube
○ Cooler water, shorter steep — Water off the boil and a short steep leave less astringency than water at a rolling boil. The second infusion is still worth drinking; after that it thins out.
○ Drying in the shade — Buds spread straight out in the sun lose their colour. Dry them spread in a breezy shaded spot, then seal them in a container and keep them somewhere cool.
△ Picking from street trees — Do not pick flowers from pagoda trees standing along traffic. Exhaust reaches them, and street trees are sometimes sprayed for pests. Buying them dried at a herb market is the better route.
△ The pods and seeds — This entry covers the flowers and buds. The constricted, bead-like pods and the seeds inside them are not eaten raw. Seeds of legume trees can carry compounds people cannot digest, so a part whose use is not established is left alone.
△ Pregnancy and breastfeeding — During pregnancy or breastfeeding, do not steep and drink the market flower on your own over any length of time. Where it is needed as medicine, discuss it with a practitioner.
△ Confusion with black locust flowers — Pagoda tree flowers are pale yellow, held upright at the branch tips in high summer; black locust flowers are white and hang in drooping racemes in May. The season and the direction differ, so identify the tree before picking.
Varieties
- Japanese pagoda tree (sapling) — The large tree planted at village entrances and in courtyards. Masses of pale yellow flowers in summer
- Weeping pagoda tree (sapling) — An ornamental selection with drooping branches, planted for the shape rather than the flowers
Source: Donguibogam, Wood Section 槐花 · Korea National Arboretum, Korean Plant Names Index