Wide-spreading species with dense foliage at grown level, for example Coreopsis lanceolata or Rudbeckia hirta, tend to eliminate slower growing shadeintolerant species. Tall, erect species, even when vigorous, have a less detrimental impact on seedlings of other species, due to reduced light-interception.
This is often important in the second and subsequent growing season for either ecological or management reasons. Species that have evergreen winter foliage will, when mixed with species that are winter dormant, restrict the use of herbicides or burning to kill or defoliate colonising weeds. In some cases, of course, this winter foliage may preclude the need to burn or herbicide, by excluding weed species. It may also, however, provide habitat for molluscs that may increase damage to spring emerging species, or simply provide too much competition for light at a critical time. In meadows, winter evergreen species, such as Papaver orientate, may decline if closely mown, restricting the timing of cutting. One of the main challenges in developing ecological plant communities is to juggle with phenology to make the planting more sustainable but still manageable. North American prairie species are problematic in northern Britain because the climate is too cool to reliably establish prairie grasses. As a result, there is no cover of dead grass on the soil surface in winter to restrict weed invasion during mild wet British winters. A shadetolerant, winter dormant, cool season tussock grass, such as Motinia caerutea, might be an effective replacement. Alternatively, a shade-tolerant, easy to establish, noncompetitive, winter evergreen, such as Festuca ovina or Primula vulgaris, might be equally successful. The author has not yet tested such plant communities. They may not work for the reasons already given, but it demonstrates the necessary thought process.