Spiraea thunbergii Seeds | Thunberg’s Meadowsweet
LATIN NAME: Spiraea thunbergii
COMMON NAME: Thunberg’s Meadowsweet
Plant Profile
Thunberg’s meadowsweet is a small, twiggy shrub from Japan and eastern China, one to one and a half metres tall, with narrow, bright green leaves only two or three centimetres long. It is the earliest of the spiraeas to flower: the small white blooms open along the whole length of the previous year’s stems in April, before the leaves are fully out, so the shrub becomes a fountain of white.
After flowering the foliage stays neat and fine-textured, and in autumn it turns a clear orange and red that is unusual in the genus. The stems are thin, brown and arching, and the plant suckers gently at the base. It was introduced to Europe in 1859 and has been planted in gardens ever since, largely because it needs no pruning to look well.
Science & Biotechnology
The species was named by the Dutch botanist Carl Peter Thunberg, who worked in Japan in the 1770s and described it in his Flora Japonica in 1784. It belongs to the rose family in the broad sense, now usually placed in Rosaceae subfamily Amygdaloideae, and the genus has been split and rejoined several times as molecular work has reshaped it.
Spiraea thunbergii is one of the parents of the hybrid Spiraea x arguta, the bridal wreath, which inherited its early flowering and its arching habit. The genus is chemically interesting because it contains salicylates, the compounds from which aspirin was developed: meadowsweet, Filipendula ulmaria, was the original source, and the old name for that plant gave aspirin its name. The spireas themselves contain much lower levels and have no medicinal use.
Uses & Benefits
This is a shrub for the front of a border or a low hedge, where its arching stems can be seen in April and its autumn colour in October. It is also one of the best spiraeas for a small garden, since it stays compact and does not need hard pruning. The flowering stems can be cut for the house in bud and will open indoors over a week.
Because it flowers on the previous year’s wood, pruning should be done immediately after flowering, removing a few of the oldest stems at the base rather than clipping the whole plant. It is tolerant of most soils, of air pollution and of light shade, though it flowers best in sun. The species has no edible or medicinal use; it is a plant for structure, early flower and autumn colour in a small space.
Growing from Seed
Spiraea seed is fine and should be sown on the surface of a light compost in spring, pressed down but not covered, and kept at 18-20 °C in bright light. Germination takes three to four weeks and is usually good.
Prick the seedlings out when they are large enough to handle, and grow them on in a cool frame rather than a warm greenhouse, since soft growth makes a weak shrub. Plant out in autumn in any reasonable soil, in sun or part shade, and cut the young plant back by half after planting to make it branch. Once established, remove a third of the oldest stems each year after flowering. The plant also roots readily from softwood cuttings taken in June, which is how named forms are kept true.
Our Take
The earliest spiraea and the neatest, with orange autumn colour that most of the genus lacks. Prune it after flowering, never before.
Related Reading
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