Hydrangea sargentiana Rehder

This distinctive member of the Hydrangea aspera complex can – at its best – make a fine foliage specimen, an unambiguously large, suckering shrub with some of the biggest leaves of the genus on splendid thick stems crowded with long, fleshy hairs. At worst it is little more than a bunch of coarse sticks bearing a few tattered leaves. Conditions are everything: moist, reasonably fertile soil, protection from wind, shade from direct sun yet with good diffuse light are the ideal conditions for this finicky species to look its best, and only a few fortunate gardeners will have a large enough space to meets its needs.

The single most distinctive feature of H. sargentiana is its indumentum. First year stems, petioles and leaf midribs are thickly covered in long, fleshy, transparent trichomes which taper from a thick base to a fine, often curled point; the general effect is rather like the stems of a moss rose (Rosa × centifolia ‘Muscosa’). They are quite different to the hairs of other species in Section Asperae, or indeed the entire genus, and are the key identification feature (Sargent 1913; De Smet et al. 2017). Coupled with ovate-oblong leaves to 30 cm long and a freely suckering habit, it gives a unique and impressive foliage effect in the garden. The flowers of the form normally seen in gardens are less impressive than the leaves, the fertile flowers a rather dull lilac, with sterile flowers pinkish white, a much less vivid contrast than in H. aspera ‘Macrophylla’, another familiar early introduction.

H. sargentiana was described by Alfred Rehder (in Sargent 1913) from Ernest Wilson’s 1907 collection W 772 (Shennongjia, W Hubei). Seed was also collected, and as usual distributed widely and efficiently by the Arnold Arboretum; in Britain the Royal Botanic Gardens Edinburgh and Kew were among the gardens to establish plants from the original gathering (Prain 1912; Elliott 2016). While subsequent herbarium sheets from Hubei and beyond have sometimes been identified as H. sargentiana (Chinese Academy of Sciences 2024), they lack the characteristic indumentum and often represent H. robusta (De Smet et al. 2015). An expedition to the type locality in 2011 refound a moderately sized, diffuse population closely matching the type, but found no other populations in neighbouring areas (De Smet et al. 2015); it seems to be a very narrow endemic deserving conservation measures.

Its place as a full species within the H. aspera complex has long been debated. Taxonomic lumper McClintock (1957) reduced it to a subspecies of H. aspera, but retained its integrity, citing only Wilson’s collection. Flora of China (Wei & Bartholomew 2001) muddied the water considerably. While the main text accepts it as a species restricted to western Hubei, the description of the indumentum seems a little vague, and co-author Bruce Bartholomew argues in a footnote that it would better be sunk entirely in a variable H. aspera, even while continuing to accept H. robusta and H. strigosa. A cytological study found that H. sargentiana has a unique karyotype within the aspera complex, although most similar to H. robusta (Mortreau et al. 2010). Unexpectedly, a plastid and nuclear DNA study using material from the type locality suggested that H. sargentiana is intimately related to the morphologically quite different H. longipes, which does occur in the area, although the authors argued that they should still be treated as distinct species (De Smet et al. 2017). Whatever its status, however, gardeners will have no difficulty in recognizing genuine H. sargentiana, at least among wild forms.

The few 20th century collections following Wilson’s have proved not to be H. sargentiana (M. Foster pers. comm. 2023). For example SICH 1801 (Daba Shan, Sichuan, 1996) as grown at Howick Hall, UK (Howick Hall Arboretum 2024) lacks the characteristic trichomes as well as having the ‘wrong’ provenance (pers. obs. 2022). However, despite some nurseries finding cuttings material sparse and difficult to root (Dirr 2021) the original collection has had a wide distribution, especially in Europe, probably helped by its free production of suckers from underground. Maurice Foster (Kent, UK) grows three accessions from different garden sources together, and finds them ‘essentially the same’ (pers. comm. 2023). It seems capable of producing spontaneous hybrids with others in the aspera complex, if only occasionally. While Maurice Foster has never found one in his uniquely aspera-rich garden (pers. comm. 2023), the author has been shown self-sown plants by both Anne Greenall and Bleddyn Wynn-Jones (UK) which seem truly intermediate in their indumentum, with fleshy trichomes present but noticeably less densely (pers. obs. 2023). Fertile hybrids between H. sargentiana and H. kawakamii have been made experimentally (Crespel, Morel & Galopin 2012; Crespel & Morel 2014). Genuinely distinct ‘good forms’ such as ‘La Fosse’ may well be hybrids which tend towards H. sargentiana, and are listed here along with all cultivars in the complex under Hydrangea aspera Species Complex Cultivars, due to genuine uncertainty and for ease of comparison. Plants with typical indumentum but narrower leaves, such as one grown at Hergest Croft, Herefordshire, UK (J. Aldridge pers. comm. 2024 – see image below) might also be unrecognized hybrids.

Winter cold is less of an issue than other environmental factors when growing this species (Haworth-Booth 1984). Away from the coldest central and northern parts of Europe and North America it has good hardiness credentials, and established plants can shoot quickly from old wood after frost damage (Bean 1981). Near its limits at Arboretum Mustila, S Finland, it is valued as a foliage plant, regularly knocked back by cold, with flowers only a rare bonus (Arboretum Mustila 2024). In St Louis, Missouri (USDA zone 7a) even plants in protected sites may lose shoots, in harsh winters being cut to the base (Missouri Botanical Garden 2024). Rather precise conditions are needed for it to reach its full magnificence as a loose, broad, large-leaved shrub to 3 m or so in height. A rich soil with constantly available moisture (but not waterlogging), shelter from wind, shade from the midday sun but plenty of light are the ideal. In addition, careful training and perhaps pegging down of shoots in the first years can help prevent the gaunt, leggy look so often mentioned (Haworth-Booth 1984).