Bracken Fern

Family

Dennstaedtiaceae

Habit

perennial

Height

2 m

Spread

3 m

Growth

fast

Lifespan

50 years

First yield

after 1 year

Hardiness

zone 3–9

Shade tolerance

partial shade

Soil

Sand, Silt, Clay

Soil moisture

very dry – very moist

pH

3.5 – 7

Edible: In East Asia the young, still-coiled fronds are a traditional spring vegetable: warabi in Japan, gosari in Korea, and eaten in China for thousands of years. They cannot be used raw. The traditional preparation is to steep the fronds in wood-ash lye or soda solution, soak them repeatedly and at length, and then boil them; only this leaches out the bitter compounds and part of the active constituents. They are served cold and marinated. The starch-rich rhizome is washed out to yield a flour, processed in Japan into the sweet warabimochi. The plant contains the carcinogen ptaquiloside, which processing does not fully remove; see the hazard notes for details.

Other uses: Before artificial fertiliser, bracken was a managed raw material. The fronds were cut in late summer and brought into stables as bedding, where they absorbed manure and went back onto the fields rich in potassium; in White Carniola it was even grown deliberately for the purpose. Burnt, it yields a potassium-rich ash from which potash for glassworks and soap boiling was extracted into the 18th century. Dried fronds served as thatch, as packing material for fruit, and as litter that slugs are reluctant to cross. Fronds and rhizomes dye wool yellowish to olive-brown. In permaculture it is chiefly of interest as a mulch and potassium source, but it should not be carried into the vegetable garden for that.

Site: With bracken the siting question is mainly a containment question. It grows on acidic, nutrient-poor, moderately moist soils in half-shade to sun, and is so competitive that it displaces everything else: the rhizome creeps up to half a metre deep and metres sideways, while decaying fronds additionally inhibit neighbouring seedlings allelopathically. Anyone planting it deliberately does so in a clearly bounded spot, behind a rhizome barrier or on ground that is meant to belong to it anyway, such as understorey along a woodland edge or as cover structure at the boundary. Not next to perennial beds, vegetables or nursery ground, and because of its toxicity not within reach of pasture or small livestock pens. Care: An established stand needs no care but does need control. The most effective way to limit it is repeated mowing or bruising of the freshly unfurled fronds in early summer, two or three times a season over several years: this exhausts the rhizome reserves, whereas a single cut merely provokes regrowth. Digging over is counterproductive, as every rhizome fragment resprouts and multiplies the stand. When cutting, wear gloves and long sleeves because of the spores and sap, and avoid dry, dusty work during spore ripening from July to September. The cuttings make a good, potassium-rich mulch, but fresh green material does not belong in a raised bed. In winter the collapsed litter is best left where it lies.

In the garden bracken propagates itself and needs curbing rather than encouraging. The decisive route is the rhizome: fragments a few centimetres long resprout reliably, which is why digging over a stand does not remove it but multiplies it. A piece of rhizome with at least one bud, lifted in spring and laid back in shallowly, establishes without further help. Spores ripen from July to September along the rolled leaf margin and germinate on moist, acidic substrate in light; the route via the prothallus stage takes months and is worthwhile only for botanical purposes. Anyone introducing it should do so only behind a root barrier or on clearly bounded ground, because an established colony is almost impossible to remove with garden means.

Bracken has no flowers and is therefore no nectar or pollen source in the usual sense; young fronds do however bear extrafloral nectaries that attract ants and other insects. Around twelve caterpillar species feed on it, three of them specialists. Its real value lies in structure: closed bracken stands are dense, tall, summer-cool cover in which pheasant, woodcock, foxes, roe fawns and many small mammals hide, and in winter the collapsed frond litter remains as overwintering quarters for insects. This cover function is ecologically real, but it stands against the other side of the ledger: where bracken dominates in bulk it displaces herbaceous diversity and tree regeneration, and it is poisonous to grazing livestock.

Notable: named from the rhizome cross-section → the dark vascular pattern resembles a double-headed eagle; in the Middle Ages "fern seed" gathered on Midsummer Night was thought to confer invisibility; one of the most widely distributed vascular plants on earth; single clones are estimated at over 1000 years old; first plant back after forest fires.

Eurasia and Africa, and as a genus almost worldwide. Pteridium aquilinum in the strict sense occurs across Eurasia and in northern and eastern Africa; closely related taxa occupy every continent except Antarctica, so bracken as a whole ranks among the most widely distributed vascular plants on earth, absent only from polar regions and true deserts. In central Europe it is common everywhere and locally shapes whole landscapes, particularly on the acidic sands of the north German plain and in the uplands. In Ireland and Scotland it blankets entire hillsides. In the Alps it climbs to around 2100 metres.

Bracken colonises open woodland, woodland edges, clear-fells, burnt ground and acidic rough grazing. It indicates moderately moist, half-shaded, acidic and nutrient-poor soils, but tolerates a wide range and retreats only from lime and waterlogging. Its branched rhizome creeps 5 to 50 centimetres deep and so survives fire, grazing and cutting: after clear-felling or burning it throws up closed mass stands within a few years that suppress all grass growth and tree regeneration. Alongside shading, allelopathic inhibition from decaying fronds contributes to this. It lives with arbuscular mycorrhiza and bears extrafloral nectaries on young fronds.