Onoclea sensibilis var. minima

Dwarf Sensitive Fern Onocleaceae

A wonderfully diminutive version of the normally rather thuggish Sensitive Fern, Onoclea sensibilis var. minima is for those who admire Onoclea sensibilis but have never quite had the courage to give it the room it demands. This little form is exceptionally slow-growing and dwarf, with delicate sterile fronds forming a compact clump rather than the roaming colonies produced by the typical plant. A German nursery catalogue gives it at only around 15 cm high and describes it as an “incredibly slow-growing and dwarf” form. (staudengaertnerei-eidmann.de)

The species is native to eastern and central North America, with a separate Asian distribution extending through eastern Russia, Korea, Japan and China. It is a fern of wet woodland, marshy ground, stream margins and other permanently moist habitats, producing soft green sterile fronds from creeping rhizomes and curious dark fertile fronds later in the season.

The name var. minima has an interesting taxonomic status. It is currently offered horticulturally, including by Edulis, but the RHS lists the name as unresolved, rather than accepting it as a formally established botanical variety. (RHS) In horticultural terms, however, its distinctively small and extremely slow-growing nature makes it a useful and intriguing plant in its own right.

As with the species, the green sterile fronds are remarkably sensitive to frost, collapsing with the first hard freeze, while the rhizome survives to produce fresh growth the following spring. The fertile fronds are shorter, dark and stiff, providing winter interest long after the soft summer foliage has disappeared.

Grow it in moist to wet, humus-rich soil in shade or dappled shade. Unlike ordinary O. sensibilis, it is particularly suited to the fernery, shaded trough or the front of a damp woodland planting where its miniature proportions can actually be appreciated.

Garden use: A collector’s form of the Sensitive Fern, excellent for small fern gardens, damp woodland margins and shaded containers. Its extraordinary slowness is both its charm and its virtue—this is Onoclea with the brakes firmly applied.

Hardiness: H5 (-15 to -10°C)
Flowering: Fern – no flowers; fertile fronds produced in late summer and persisting into winter
Height: 15–30 cm
Spread: 30–50 cm