Establishment and development of ornamental grasses on green roofs and living walls

Abstract

Ornamental grasses are often used in gardens to improve biodiversity and as additional aesthetical resources. However, their use in green roofs (GR) and living walls (LW) is not so widespread and it has not been studied extensively. The aim of this work is to assess the performance of seven grass species (Imperata cylindrica ‘Red Baron’, Acorus gramineus, Stipa tenuissima ‘Pony Fails’, Carex flagellifera ‘Bronzita’, Carex oshimensis ‘Evergold’, Uncinia rubra ‘Everflame’ and Miscanthus sinensis) for their use in GR and LW. The growth of the plants was evaluated (i.e. biomass production, dimensions), as well as their visual quality and survival. C. flagellifera and C. oshimensis showed coverage levels greater than 75% and good visual quality, while A. gramineus reached 55–60%. I. cylindrica and M. sinensis showed coverages slightly below 50% in the LW, however, both performed well in the GR, though with a lower visual quality. U. rubra did not develop well, reaching the lowest coverage (below 45%) but maintaining a high visual quality. S. tenuissima also attained low coverage in the LW and presented high mortality, especially in the GR. In LW, C. oshimensis stood out in flowering, while S. tenuissima showed the highest flowering rate in GR. The species should be selected considering their characteristics and performance in order to achieve a correct appearance and development. Interspecific interactions are especially important in LW, as species with upward growth should be placed above species with fallen leaves, not below.

Vertical plants: Plant design of Living walls – evaluation of 34 perennials in a textile based Living wall over a three years experiment

“…We observed differences in plant development depending on the climate and light conditions. Plants in LW do not grow so high, which could be due to less space for roots and the shoot (Suaŕez-Caćeres et al, 2022). The main difference between the experiment years was the hard winter between 2017 and 2018, where we observed that the plants needed more time to recover after the hard winter.…”

“…Perennials that had the same genre compared to our study were: Achillea millefolia, Asplenium nidus, Bergenia ssp., Bergenia cordifolia, Carex brunnea, Carey morrowi, Geranium sanguineum, Iris sibirica, Polystichum rigens Tagawa, Tradescantia spathacea and Tradescantia zebrina. Also, ornamental grasses could be suitable for LW because they are visually attractive and need low maintenance (Suaŕez-Caćeres et al, 2022). At the beginning of our research, we hypothesised that we would find a higher variety of suitable plants for LWs.…”

“…First, we wanted to know what the plants looked like during the different seasons. We used different perennials and assumed that it is possible to create attractive plant plans for LW because of the plants ornamental effects: sizes, texture, or colour (Suaŕez-Caćeres et al, 2022). Our research project took three years, and we saw differences in plant aesthetics between the experiment years.…”

“…There were species that showed similar and different growth forms, as is the case in horizontal planting as well. The plants in our system were planted vertically, which means they grew parallel to the normal ground (Suaŕez-Caćeres et al, 2022). This 90°rotation led to an adapted growth direction of some species.…”

“…For the composition of the plant plan, the designer must consider the "right" place for the species: Plants should not overlay each other and should all get enough light (intra and interspecific interactions). In addition, to reach a closed coverage, the growth form or dimension ("up" and "down"), the "volume", and also the "horizontal space" should be considered (Suaŕez-Caćeres et al, 2022). Another factor to consider is plant combination.…”