Although not frequently mentioned in common usage, rockwork was much discussed in treatise literature, particularly in the nineteenth century when the feature became popular. The aesthetic and associative possibilities of rocks in landscape design had been recognized since at least the eighteenth century. Thomas Whately, in Observations on Modern Gardening (1770), included a chapter about rocks in which he insisted that they be regarded as part of an aesthetic ensemble. He wrote,
Rills, rivulets, and cascades abound among rocks; they are natural to the scene; and such scenes commonly require every accompaniment which can be procured for them: mere rocks, unless they are peculiarly adapted to certain impressions, may surprise, but can hardly please; they are too far removed from common life, too barren, and inhospitable, rather desolate than solitary, and more horrid than terrible. . . . In the choice and the application of these accompaniments, consists all our power over rocks; they are themselves too vast and too stubborn to submit to our control; but by the addition or removal of the appendages which we can command, parts may be shewn or concealed, and the characters with their impressions may be weakened or enforced: to adapt the accompaniments accordingly, is the utmost ambition of art when rocks are the subject.
Their most distinguished characters are, dignity, terror, and fancy: the expressions of all are constantly wild; and sometimes a rocky scene is only wild, without pretensions to any particular character. 
By the nineteenth century, artificially constructed mounted arrangements of rocks, known as rockwork (or rockery), had become a recognized garden feature. Edward Sayers (1837) considered a well-designed rockery to be the finishing touch to a designed landscape. In 1828, Noah Webster defined rockwork simply as “stones fixed in mortar” to imitate rocks. In 1848, however, he elaborated upon this definition, describing the term as an elevated construction composed of earth and other materials covered with rock, devoted to growing plants suited to this environment. Indeed, George William Johnson, in A Dictionary of Modern Gardening (1847), advised strongly that plants should be the focus of a rockwork.
The primary stimulus for the development of rockwork was the interest in and availability of specialized plants and shrubs that required special soil and climatic conditions. The shallow soil typical of the feature and the radiant heat of sun-warmed rocks permitted the growth of vegetation that often would not flourish in other areas of the garden. James E. Teschemacher, for example, recommended imported Alpine plants for rockworks; James Arnold planted his rockwork with verbena and petunias; and Sayers suggested rhododendrons and kalmias, shrubs that were prized by plant collectors.  A description by C. M. Hovey in 1846 of W. H. Corcoran’s rockwork suggests how the feature might have been watered through an elaborate irrigation system.
Treatise writers provided homeowners with considerable advice regarding the construction of rockworks. Most writers recommended employing natural rock, although it is clear from Johnson’s discussion that cement was used liberally in addition to other durable materials, such as bricks. Johnson even suggested using soil and rubbish to construct the core of the mound, which was then covered with rocks. As to the type of rock, British author J. C. Loudon and American author A. J. Downing advised using rocks from local geological formations. Jane Loudon (1845) argued that relying on “one kind of stone has always a better effect,” while American writer Robert Buist (1841) recommended the “greatest possible variety of character, size, and form.” Nonetheless, he insisted that rocks of the same kind and color should be placed near each other. In this vein, most treatise writers recommended constructing the rockwork so that the feature would appear natural. Apparently, this result was not easily achieved, as suggested by Downing’s comment in 1851 that rockworks were “dangerous features.” If the rockwork appeared artificial, he explained, it would be “offensive to good sense and good taste.”
Placement of the rockwork also greatly concerned treatise writers, who repeatedly advised that appropriate locations be selected. Authors disagreed, however, as to what made the best position. Jane Loudon, for example, recommended “an open airy situation,” while Joseph Breck (1851) insisted that it be concealed from the “general flower-garden” and shaded for the benefit of the plants. Rockworks were usually sited near the greenhouse (providing a mutually reinforcing display of plants and allowing ease in transplantation), in distant areas of the pleasure ground (along walks where gravel provided a visual connection to the rockwork), or near bodies of water. When constructed as part of a water feature, a rockwork could support aquatic plants [Fig. 1].
-- Anne L. Helmreich
- Thomas Whately, Observations on Modern Gardening, reprint of 1770 ed. (London: Garland Press, 1982), view on Zotero. For more about the history of rockwork, see Dennis Lambin, “From Grottos to the Alps: A Contribution to a History of Rock and Alpine Gardens,” Journal of Garden History 14 (1994): 236–56, view on Zotero.
- The plant list provided by George William Johnson in 1847 in his definition of rockwork is a helpful guide to the range of plant material associated with rockworks. Since he was writing primarily for a British audience, however, this list must be treated with caution when considering the American context.