In naturally occurring plant communities, spatial arrangement often varies according to the site productivity and the levels of environmental stress. On highly productive, low – stress sites, for example moist fertile soils adjacent to a lake or river, tall vigorous herbaceous plants, which often spread by rhizomes or stolons to form large monocultural patches, eliminate other species in the process. Cultivated species typical of these situations include Filipendula, Lysimachia, Helianthus laetiflorus and Solidago gigantea. On low-productivity, high-stress sites, for example a south facing slope on dry limestone soils, short, slow-growing clump-forming herbaceous plants are favoured. In contrast to highly productive sites, low-productivity conditions tend to support a high diversity of different plants because no plant has the means to dominate its neighbours. Species occur as individuals or small groups, repeating across the site and intermixed with individuals of other species.
Sites that are intermediate between these two extremes will host a mix of individuals, small groups and occasional monospecific patches. These natural patterns should inform design. If one tries to implement a dry infertile planting concept on a fertile productive site, the most vigorous weeds and planted species (and especially those with spreading rhizomes, etc.) will always be trying to colonise and eliminate their less vigorous neighbours. Consequently, larger blocks of species are more sensible on productive sites, and are also satisfactory on unproductive sites, although visually they may not fit the anticipated visual stereotype for such sites. Typically, the pattern of repeating individuals is likely to be visually preferred on unproductive sites (Figures 6.13 and 6.14).