<em>Platycodon</em>: planting, cultivation, care

Description and botany

The Platycodon, also known as “Japanese bellflower” or “large-flowered bellflower”, is a perennial of family Campanulaceae, native to grassy slopes and high-altitude prairies of the Far East from China to Siberia, via Japan and Korea.

The Platycodon grandiflorus or “large-flowered Platycodon”, is the only species of the genus. Its original violet-blue flowers are however available in some cultivars with pink or white flowers and in series such as ‘Fuji’ or ‘Astra’, which offer dwarf, compact forms.

Platycodon develops from a thick fibrous, almost tuberous root into a rounded, upright clump with an open habit, reaching 10 to 60 cm in height and about 30 cm spread. A little slow to establish, Platycodon needs around two years to fill out properly and become fully floriferous. Slow growth matched by great longevity: once well rooted, this perennial grows year on year to form dense, bushy clumps or flowering mats.

The plant produces a regular clump of slender leafy stems, sparsely ramified, bearing small deciduous leaves 3 to 5 cm long. Simple, ovate, lanceolate, with irregularly dentate margins, they are whorled at stem bases and alternate towards stem apices. Edible, its young spring shoots can be eaten raw in salad. A pleasing matte green to bluish-green, often glaucous beneath and sometimes marginate with red, leaves can turn reddish in autumn before dying back.

Flowering of exquisite delicacy and remarkable generosity stands out against this lovely grey-tinged foliage, which seems to disappear beneath an avalanche of pastel-coloured flowers. It is spread through summer. At tips of the erect stems and in leaf axils, from June to September, depending on climate, appear curious globose floral buds shaped like small green balloons, hence the English name “balloon flower” or “balloon flower”.

These large, ball-like buds open into big, star-like cup flowers with five pointed petals. Some cultivars bear double or semi-double flowers. These well-defined narrow bell-shaped flowers, 3 to 7 cm across, resemble those of its bellflower cousin.

Platycodon in bud and in flower

Bud colours ranging from acidic green to pinkish-yellow turn at opening into a unique blue shaded with lavender or violet, sometimes pure white or pale pink, depending on cultivar. With a pearly texture, the delicately veined petals reveal fine veins of a deeper shade across the corolla.

These large flowers are also edible and very attractive in country-style bouquets.

This ceaseless flowering attracts many pollinating insects. It is followed by autumn fruits, inflated capsules containing numerous tiny black seeds.

Hardy to -30°C, tolerant of heat and easy to grow, Platycodon thrives in non-scorching sun or partial shade in warm regions, in any good, fresh, rather fertile and well-drained garden soil.

It is used in beds, rockeries, borders and even in a large pot on terrace or balcony.

In Japan, the flower of Platycodon is often represented in stylised form in decoration. In traditional Chinese, Japanese and Korean medicine, Platycodon root is credited with anti-inflammatory medicinal properties.

Main species and varieties

Le Platycodon grandiflorus is the only species of the genus. It is declinated into a few cultivars with pink or white flowers and is now offered in seriates such as ‘Fuji’ or ‘Astra’. The latter seriate offers dwarf, compact forms not exceeding 30 cm in height.

Most popular

Platycodon grandiflorus Mariesii

Produces abundant intense blue flowers throughout summer. Forms robust, bushy clumps for edging borders or mid-border positions.

• Flowering time August, September
• Height at maturity 40 cm

See the product sheet

Our favourites

Platycodon grandiflorus Fuji White

A variety with large bell-shaped flowers, pure white. Plant at edging or mid-border positions.

• Flowering time August, September
• Height at maturity 50 cm

See the product sheet

Platycodon grandiflorus Perimutterschale

Its flower buds shaped like balloons open into large star-shaped flowers of pale, pearly pink. Plant in border or along a path. Also grows very well in a pot.

• Flowering time July to October
• Height at maturity 25 cm

See the product sheet

Planting

Where to plant Platycodon

Very hardy, Platycodon withstands cold (sometimes down to -35°C) as well as high heat, making it a very easy-to-grow flower across France. It grows in non-scorching sun, preferring light shade in hottest regions.

Adaptable, it tolerates all soil types, even calcareous, but will thrive in good garden soil — rich, deep, well-drained, light and cool — that does not dry out: it will tolerate summer drought provided soil remains cool. Although it copes well with occasional drought, it dislikes wet winters: waterlogged, heavy clay soil will shorten its lifespan.

Think carefully about position because its tuberous root sometimes takes time to establish and will hate transplanting.

It fits perfectly into natural gardens, as a neat edging or as background in a large romantic perennial bed. It tolerates enough shade to deserve a place in a semi-shaded border or in the more shaded parts of a wooded garden. Plant en masse along path edges. Reserve dwarf varieties for large summer containers and cool rockeries.

Platycodon in its setting (photo cultivar413-Flickr)

When to plant Platycodon

Preferably planted in spring, from February to April in cold climates, or in autumn from September to November in mild climates.

How to plant Platycodon

In open ground

The Platycodon grandiflorus prefers soils that remain cool through summer and are well drained. Add plenty of well‑rotted compost if soil is poor. In very clayey soil, add compost or at least one-third grit to lighten it and improve drainage. If your soil holds too much moisture, plant on top of a mound or on an elevated bank.

Allow 5 to 8 plants per m2 and space 20 to 40 cm between each young plant.

• Dig a hole two to three times the volume of the bucket
• Fork soil deeply, remove stones and weeds
• Add well-draining gravel to base of hole
• Add a good spadeful of well-rotted compost to soil
• Position the rootball
• Backfill, collar at soil level
• Water regularly to ensure good establishment in first days after planting, then more sparingly
• Apply mulch to keep soil cool

Planting Platycodon in a pot

Plant the Platycodon in a deep pot at least 30 cm in diameter to allow its fleshy roots to develop freely. Although Platycodon adapts well to container culture, it is not a houseplant — keep outdoors in winter; very hardy, it does not fear cold!

• Spread a good drainage layer of grit or expanded clay balls in bottom of pot
• Plant in a slightly sandy mix of potting compost for geraniums or flowering plants
• Water
• Mulch around base

Care and maintenance

Undemanding, the Platycodon requires very little care, withstanding drought in cool soil as well as harsh winters.

Mulch the soil at the end of May so it stays cool throughout summer and water regularly during dry spells.

A fairly heavy feeder, Platycodon prefers fertile soils: it will appreciate you lightly forking in a little compost or manure at its base each year at the end of winter.

Remove faded flowers regularly to prolong flowering.

Platycodon dies back completely in winter; remember to mark its position well in autumn to avoid pulling it up accidentally while weeding!

In autumn, using a pruning shear, prune all flower spikes by cutting the clumps back to ground level. Leave them to set seed if you want to save them for sowing.

In a pot, Platycodon needs a lot of water: never let the potting compost dry out. To support its flowering, apply a fertiliser for flowering plants once a week.

Potential diseases and pests

Platycodon is a disease-resistant perennial. Slugs and snails can attack young shoots when they appear in spring. And because it dies back completely in winter, emerging very late in spring, not before April–May, it is recommended to mark its location in autumn so you can keep gastropods away when shoots emerge. Discover our advice on controlling slugs!

Propagation of Platycodon

Platycodon multiplies easily by sowing. Division of clumps in spring is also possible, although more delicate, as once established plant does not like to be disturbed.

By sowing

You can collect seeds from the year at end of summer and sow them in spring.

• In April sow Platycodon seeds under cover in a seed tray or in an individual bucket (1 to 2 seeds) in a mix of potting compost and turf
• Cover seeds lightly with potting compost
• Firm down and keep soil moist until germination, which occurs in three to six weeks
• Place your sowings out of direct sunlight
• Prick out seedlings into buckets in autumn
• Plant young plants in garden or in larger pots the following spring

Direct sowing outdoors

• In well-tilled soil enriched with potting compost, sow thinly directly in place and out of direct sunlight
• Cover with a thin layer of potting compost without burying deeply
• Firm down and water until germination (2 to 3 weeks), keeping soil moist
• Thin out after germination, keeping only one young plant every 30 to 40 cm
• Protect from slugs

Division

Divide the most mature stumps and only resort to this risky operation if plant shows signs of decline because Platycodon roots do not like being disturbed.

• Using a fork and spade, lift the rootball gently; roots are fragile
• Separate a few clump offsets with roots
• Replant immediately in garden in well-tilled soil

Associate

Platycodon flowers will bloom abundantly from late spring to early autumn surrounded by other summer-flowering perennials that are easy-to-grow. It is useful for bringing blooms to gardens in summer, during flowering lull and indispensable in scenes of a romantic garden.

At edge of a border it will add a delicate, neat touch when planted with roses, poppies, paniculate phlox, ornamental alliums, foxgloves, aconites or gypsophilas. In a rockery, surround it with other low-growing plants such as bellflowers and clumps of dwarf Dianthus.

An example of a planting combination: Rose ‘Ballerina’, Rose ‘Scepter’d Isle’, Thalictrum actaefolium ‘Perfume Star’, Selinum wallichianum, Geranium ‘Johnson’s Blue’, Platycodon grandiflorus ‘Perlmutterschale’

Flowers of pastel‑toned cultivars will reign in a pink garden or a white garden; they cannot compete with bright, garish colours but look very effective with purple or variegated-with-white foliage such as heucheras and bugles. They are particularly attractive set against green, silver or glaucous foliage of ferns, hostas, hardy geraniums and Echinops. They provide a striking contrast with green‑yellow flowers and leaves of alchemillas and Pennisetum grasses.