Carex

When is a ‘grass’ not a grass ? On most occasions that I have cause to communicate with clients about plantings, I’m not particularly drawn towards providing an answer to this question – as I’m not convinced that it’s a burning issue for those outside of botany and horticulture. However, the distinction between the family to which the genus Carex belongs (the sedges) and the grass family (Poaceae) is pronounced, and worth understanding for the differing aesthetic qualities that they bring to plantings (especially in the north of New Zealand).

In basic design terms, one distinction stands out for me between the appearance of commonly-cultivated Carex species and the appearance of true grasses within meadows, prairie-type plantings (in the wider context of Northern Hemisphere landscape design) and tussocklands. In contrast with the moving, diaphanous mantle that grasses often provide (especially in seductive images from plantings overseas), carices¹ usually have a more ‘grounded’ form and, in the case of many species, read more emphatically as individual plants than as part of a continuous fabric.

One factor that contributes to this impression is the fact that Carex spp. do not generally develop the kinds of upright, lightweight flowerheads that grasses like our native Chionochloa tussocks or popular European species like Molinia caerulea and Calamagrostis acutiflora often produce. Even everyday pasture and turf grasses (such as fescue and browntop) regularly bear frothy flowerheads of this nature.

These observations are significant for our design work, as they influence the way in which we normally use Carex spp. in plantings. When one observes many species in the wild, they tend not to grow in dense masses in the way that they are often planted in landscape work. In strictly visual terms, allowing some space between individual plants of Carex just looks better, with mass plantings frequently registering as a poorly-executed exercise in crowd control.

Recently, Carex‘s ranks within New Zealand have swelled with the taxonomic demise of the erstwhile genus of sedges, Uncinia (the hook grasses, or bastard grasses), which has been deemed to sit better within Carex. Consequently, more than 110 species of Carex are recognised as being native to New Zealand, many of which are popular amongst gardeners and the landscape trade.

Certain species (such as the orange-tinted Carex testacea) have attracted attention on the basis of the vivid tones that the foliage takes on in response to particular environmental conditions. In the case of C. testacea, its leaf colour is a common adaptation to the high light levels and drought that plants must endure in sand dunes, such as at Spirits Bay (where the image below was taken) – with other examples being the sandbinder, pingao (Ficinia spiralis), and the creeping sand coprosma (Coprosma acerosa). Other species exhibit hues of brown (such as the popular Carex buchananii), cream (as in Carex fretalis) and red, whilst the sheer variety of shades of green opens up a wide range of possibilities for plantings.

In winter, the mantle of snow that stretches over skifields offers few clues towards the presence of finely detailed, natural ‘gardens’ beneath, waiting to reappear once again after the spring thaw. On the Remarkables Ranges above Lake Wakatipu, Lake Alta (which sits within the boundaries of the skifield) drains out into a network of seepages that provide the requisite conditions for beautiful herbfields and cushion bogs.

The deep red foliage of Carex berggrenii brings a dramatic shift in tone to the margins of these watercourses (as compared with the undulating green sward that surrounds it), forming mounds of compact turf within the flowing water. That colour (which is akin to red wine) has brought this species to the attention of many native horticulturists, including Oratia Native Plant Nursery (where I first encountered it).

Having experimented with its cultivation several years beforehand, viewing it in the wild for the first time demonstrated the kind of conditions that one needs to provide in order to grow this species well. Although it will adapt to a life outside of running water, it will not withstand extended periods of drying out, and it achieves its finest appearance in the kind of situation pictured above.

C. berggrenii is not the only sedge to have been introduced into cultivation on account of red pigmentation in the leaves – a characteristic that is evidently associated with damp habitats. The much larger Carex tenuiculmis (which has long trailing leaves and an attractive habit) occupies similarly moist environments and has been commonly used in the landscape industry (and gardens) for a long time. Carex uncifolia is an attractive threatened species that grows to a similar scale to C. berggrenii, yet which bears narrow, wispy leaves and tends to develop into more compact clumps.

It is unsurprising that this species has been grown by nurseries outside of New Zealand, and I expect that it would be more commonly seen in gardens from cooler parts of our country, if not for its preference for damp habitats (which has undoubtedly led to many false starts within plantings). C. berggrenii occurs naturally throughout much of the South Island and in a few places in the Central North Island, and is officially classed as ‘Naturally Uncommon’. It was named (by the eminent 19^th Century botanist, Donald Petrie) in honour of Dr Sven Berggren, of Uppsala University – a Swedish botanist who travelled to, and collected plants within, New Zealand in the 1870s.

Subtlety is a quality that is too often underappreciated in plants. Landscape design and horticultural retail can both easily veer towards emphasising the point-of-sale appeal of plant species and cultivars (particularly as individuals), to the extent that plant communities within gardens end up as a discordant cacophony of strident forms and characters, jostling for position.

The ‘quiet’ voice offered by species such as Carex inopinata brings balance into natural and artificial plant associations – a role that was a significant factor in the increased use of ferns and grasses in gardens (as in the pioneering work of Jens Jensen or Karl Foerster). Furthermore, they ingrain plantings with a character that I consider to be one of the finest (and most challenging) qualities that one can achieve within planting design – the sense of a composition that is ‘effortless’.

Although this is a significant reason for our interest in Carex inopinata, this is not the only advantage that this diminutive, fine-leaved sedge provides. As a resident of dry, open woodlands and rock overhangs (such as the large schist outcrop pictured at the base of this profile, from near Alexandra), Carex inopinata is capable of withstanding both extreme drought and intense shade (conditions that present a major challenge at the point where architecture and landscape design quite literally meet).

Within the kinds of dark habitats that C. inopinata is able to occupy, the vibrant green hue of its foliage (as demonstrated above left) is a particularly welcome tone. Familiarity with the gamut of greens exhibited within the plant world is an essential part of our dialogue whilst working on planting designs, and when observing plants in the wild.

With respect to this species, the contrast between its iridescent, light green colour and the darker, weightier tone of a low-growing fern, Pellaea falcata, (at Kowhai Point Scenic Reserve) is a particularly useful study for how differences in shades of green might be handled in designed environments.

C. inopinata (which is classified as nationally threatened) is one of several grass-like species associated with dry, fertile sites in eastern parts of the South Island – including a grass, Simplicia laxa, that endures in similarly unpromising habitats (such as rock overhangs) where more aggressive exotic weeds are unable to outcompete it.

This raises an interesting point when one encounters species such as Carex inopinata, insofar as the current picture provided by the wild places in which it remains do not necessarily represent preferred habitats. Instead, such places constitute refugia to which such species have retreated in the face of large-scale landscape changes; notably the spread of aggressive, exotic pasture grasses and environmental weeds through the country.