Green roofs could be a way to increase vegetation in the center of old Mediterranean cities. The need for conservation of local character and biodiversity requires the use of native plant species, whereas the deficiency of water, particularly in semiarid regions, requires the use of species with reduced irrigation needs. Moreover, the aged buildings lead to the use of lightweight green roof constructions. Therefore, research was undertaken to investigate the possibility of using three Mediterranean aromatic xerophytes, Artemisia absinthium L., Helichrysum italicum Roth., and H. orientale L., at an extensive green roof in Athens, Greece. Simultaneously, the possibility of using locally produced grape marc compost was investigated. Substrate type and depth and irrigation frequency effects on growth of these species were studied. Rooted cuttings were planted mid-May in plastic containers with a green roof infrastructure fitted (moisture retention and protection of the insulation mat, drainage layer, and filter sheet) and placed on a fully exposed third floor flat roof at the Agricultural University of Athens. Two types of substrates were used, grape marc compost:soil:perlite (2:3:5, v/v) and peat:soil:perlite (2:3:5, v/v, as a control), as well as two substrate depths, 7.5 (shallow) and 15 cm (deep), and two irrigation frequencies, sparse (5 or 7 days in shallow and deep substrate, respectively) and normal (3 or 5 days in shallow and deep substrate, respectively). Increased contents of macroelements, total phosphorus (P) and potassium (K) in particular, were recorded in the compost-amended substrate, whereas both substrates had similar physical properties. Plant growth was recorded from May to October. The deep compost-amended substrate, independent of irrigation frequency, resulted in taller plants with bigger diameter and aboveground dry weight in all species. However, a remarkable result was that shallow compost-amended substrate with sparse irrigation resulted in similar or even bigger plant growth of all plant species compared with deep peat-amended substrate with normal irrigation. Thus, all three species were found suitable for use in Mediterranean extensive or semi-intensive green roofs, whereas the use of grape marc compost in the substrate allowed for less water consumption and the reduction of substrate depth without restriction of plant growth at the establishment phase and the first period of drought.

Rooted cuttings of Dendranthema grandiflora Tzvelev., Nerium oleander L. and Lantana camara L., as well as seedlings of Pelargonium zonale L. were grown in media containing cotton gin trash compost, rice hulls, peat and perlite in various ratios, and their vegetative growth and flowering was determined and compared with a control medium of 1 peat:1perlite (by volume). When up to 60% of peat in the control medium was replaced by cotton gin trash compost plant height was slightly reduced, except in P. zonale, the number of flowers was increased, except in pot D. grandiflora, and flowering was accelerated in all species except N. oleander. When half or all the perlite of the control was replaced by rice hulls, plant height and flower number was similar to that of the control plants, except in pot D. grandiflora where the number of flowers was reduced and in cut D. grandiflora where both stem length and flower number were reduced; also, in L. camara total replacement of perlite by rice hulls gave shorter plants. In media that contained cotton gin trash compost, peat and rice hulls, plant height of all species except P. zonale was reduced. Partitioning of cotton gin trash compost or rice hulls in the media decreased their total porosity and their easily available water, while cotton gin trash compost increased bulk density. When rice hulls totally replaced the perlite, bulk density was decreased. The media with peat, cotton gin trash compost and rice hulls and the one with peat and rice hulls had the lowest easily available water and total porosity of all the media tested. Media with cotton gin trash compost had a high electrical conductance at the beginning of the culture period, but it fell to the level of the control by the end.

Sages are medicinal and aromatic plants that constitute a large pool from which active compounds of great pharmaceutical potential can be derived, while at the same time, they also have ornamental value. The purpose of this study was to develop the micropropagation protocols of Salvia fruticosa, S. officinalis, S. ringens, S. tomentosa, and S. pomifera ssp. pomifera to facilitate their exploitation in the pharmaceutical and floriculture industries. In vitro cultures of S. ringens and S. pomifera ssp. pomifera was studied for the first time. Shoot tips and single node explants from in vitro seedlings were initially cultured on hormone free (Hf)-MS medium, followed by subcultures on MS medium supplemented with 6-benzyladenine (BA) for all species, as well as with zeatin (ZEA), kinetin (KIN), 6-(γ,γ-dimethylallyamino) purine (2iP), or meta-topolin (mT) for S. fruticosa and S. officinalis, at concentrations 0.0 to 3.2 mg L⁻¹, in combination with 0.01 mg L⁻¹ 1-naphthaleneacetic acid (NAA). S. officinalis was the most efficient in shoot multiplication of all the studied species. The highest multiplication indices were found using 0.8 mg L⁻¹ BA for S. fruticosa, 0.4 mg L⁻¹ BA, or mT for S. officinalis, and lower than 0.8 mg L⁻¹ BA for the other three species. Hyperhydricity was a problem at the multiplication stage, and was most pronounced in single node explants, increasing in proportion to cytokinin concentration. Microshoots rooted at high percentages (75–85%) on half-strength MS medium with 0.0 or 0.5 mg L⁻¹ Indole-3-butyric acid (IBA), except for those of S. ringens, which rooted best at 1.0–2.0 mg L⁻¹ IBA. Ex vitro acclimatization was highly successful (80–95%) on peat–perlite substrate (1:1 v/v). Thus, the present study resulted in efficient micropropagation protocols for five Mediterranean sage species native to Greece, which will facilitate breeding programs and the promotion of these species in the floriculture and pharmaceutical industries.

Native-to-Greece sage species, namely, Salvia fruticosa, S. officinalis, S. pomifera ssp. pomifera, S. ringens, S. tomentosa and interspecific hybrids, were evaluated for their acclimatization in an extensive Mediterranean green roof during summer under regular and reduced irrigation (every 2–3 days with substrate moisture 16–22% v/v and 4–5 days with substrate moisture 7–11% v/v, respectively). A substrate (grape-marc compost:perlite:pumice, 3:3:4, v/v) that was 10 cm deep was used. Regardless of the irrigation frequency, S. pomifera ssp. pomifera × S. ringens and S. officinalis × S. pomifera ssp. pomifera showed the highest survival of all hybrids and species, along with satisfactory growth, while S. fruticosa showed the lowest survival. Reduced irrigation resulted in the reduction of aboveground and root biomass, with no damage to the photosynthetic apparatus. S. fruticosa showed the highest (53%) aboveground biomass reduction and S. officinalis, S. officinalis × S. ringens and S. pomifera ssp. pomifera × S. ringens showed the lowest (28, 23 and 3%, respectively), while S. officinalis × S. pomifera ssp. pomifera and S. pomifera ssp. pomifera × S. ringens showed the lowest reduction in root biomass (13 and 16%, respectively). With a reservation for S. fruticosa, Greek Salvia spp. and their interspecific hybrids studied in the present work are recommended for sustainable exploitation in extensive green roofs in arid regions and generally in xeriscaping.

Salvia tomentosa is a perennial sage of the maquis vegetation, strongly aromatic, with medicinal and ornamental value. Aiming to facilitate the promotion of the species in the floriculture sector, its micropropagation was studied in terms of the effect of explant origin and medium plant growth regulators on in vitro cultures establishment, shoot proliferation and rooting. Shoot tip or single node explants excised from either in vitro grown seedlings or greenhouse plants grown from cuttings of mature plants were cultured on MS medium supplemented with 6-benzyladenine (BA) at concentrations 0.0–3.2 mg L⁻¹ in combination with 0.0, 0.01 and 0.1 mg L⁻¹ 1-naphthaleneacetic acid (NAA). Infections were the biggest problem for establishing cultures from greenhouse plants, while explants from in vitro seedlings showed hyperhydricity, especially the nodal ones. In the multiplication stage, high BA concentrations reduced explant response to produce shoots as well as the length of shoots produced, and although they increased shoot number per responding explant, a large number of shoots were hyperhydrated especially in explants of seedling origin. In general, the highest multiplication indexes, relevant to normal shoots, were given by the hormone-free medium or one with low BA concentration, and by shoot tip explants originated from greenhouse adult plants. The highest rooting rates (70–78%) were achieved either at full or half strength hormone-free or with 0.1 mg L⁻¹ indole-3-butyric acid (IBA) medium. Increasing IBA resulted in an increase in root number, but a decrease in rooting rate and root length. Ex vitro acclimatization was highly successful (92–96%) in peat-perlite (1:1 v/v) substrate. The micropropagation protocol developed will contribute to the promotion of S. tomentosa in the floriculture and pharmaceutical industry and will be a tool for breeding programs targeting high value products.