Physical and Chemical Properties of Green Roof Media and Their Effect on Plant Establishment (Publication: Journal of Environmental Horticulture)
There are few research reports on components of green roof media. Better elucidation will allow landscape installers to select the ideal medium for individual or regional situations. The present study examined the effects of heat-expanded clay media components on: (1) physical and chemical properties and (2) growth of Sedum floriferum (stonecrop) and Dianthus gratianopolitanus (dianthus) plugs on a green roof. The addition of fine grade components caused an increase in bulk density and a decrease in total porosity, aeration porosity, and aeration porosity at applied suction pressure of 6.3 kPa. Container capacity reached a maximum following the addition of 40–60% (by vol) fine grade particles. Stonecrop and dianthus plugs were planted in early summer (June 29, 2010) into 6.4 cm (2.5 in) depth media containing 10–60% fine or medium grade heat-expanded clay located in a green roof garden. By early autumn (October 3, 2010), dianthus cover and plant weight were greatest in media containing 50–60% fine grade heat-expanded clay or 60% medium grade heat-expanded clay while stonecrop growth was inadequate regardless of media type.
Effects of enhanced APG surfactant on leaching and wettability of six bark substrates (Publication: HortTechnology)
Alkyl phenol ethoxylate (APE) surfactants are used in horticultural substrates but are considered non-biodegradable while others such as alkyl polyglucoside (APG) are derived from biodegradable sugar compounds.
APE reduced total porosity (TP), container capacity (CC), and aeration porosity (AP) while APG with polyalkylene oxide block co-polymer surfactant (APG/BLK) increased TP, CC, and AP for some substrates but other substrates remained unaffected by either surfactant.
We determined substrate leaching fraction (LF) and wettability rating (WR) following drenches of 0.003 to 0.2 mL·L-1 APG/BLK for six bark substrates for three wetting cycles. Following the third wetting cycle five substrates had reduced LF and increased WR. Drenches of 0.2 mL·L-1 APE or APG/BLK for three wetting cycles indicated that APE was more efficacious than APG/BLK for reducing LF or increasing WR.
APE was determined to be an effective surfactant for difficult-to-wet substrates but drenching sometimes reduced total porosity. No reductions in total porosity were noted when using APG/BLK. Drenching rates of 0.003-0.2 mL·L-1 APG/BLK for three successive wetting cycles reduced LF and increased WR for most substrates, indicating potential usage for some horticultural applications.
Use of confocal microscopy to relate germination vigor to embryo morphology of dormant and non-dormant purpletop (Tridens flavus)(Publication: Seed Science and Technology)
We describe a novel method to evaluate caryopsis germination vigor of a warm-season grass that is native to the United States. We developed a protocol to rapidly view high resolution confocal images of the purpletop (Tridens flavus) embryo in dormant and non-dormant (scarified) caryopses.
Whole purpletop seed were cryo-sectioned until embryos were exposed, stained, and viewed with a laser scanning confocal microscope. Following a four-day incubation, dormant caryopses compared to non-dormant caryopses had 10 and 38% increased embryo and radicle lengths and 9, 11, and 44% increased main axis, embryo, and radicle widths, respectively.
Changes in embryonic structures of non-dormant caryopses compared to dormant caryopses were concomitant with decreased days to 10% germination (G10), days to 50% germination (G50), and days to 90% germination (G90), but were not concomitant with final germination percentage (FGP) or germination synchrony (G10-90). G10, G50, and G90 of dormant caryopses were 18.8, 25.4, and 34.7 days, respectively, while those for non-dormant caryopses were 4.1, 9.6, and 22.3 days.
In conclusion, decreased G10, G50, G90, and increased length of radicle and widths of main axis and radicle were concomitant with subsequent rapid germination of non-dormant caryopses, but not dormant ones, and may be useful criteria for establishing seed vigor.
Effects of peat moss substitution with arboretum and greenhouse waste compost for use in container media (Publication: Compost Science and Utilization)
Plugs of impatiens (Impatiens wallerianaHook.f.), salvia (Salvia splendens Sellow ex Roem. & Schult.), and vinca (Catharanthus roseus (L.) G. Don) were transplanted into containers filled with commercial Sphagnum peat moss plus perlite medium (Sunshine Mix #1) or arboretum and greenhouse waste compost (CT), Sphagnum peat moss (PS), and perlite (PE) medium at percentages of (by vol.) 50:50 PS:PE and 75:25 PS:PE (controls). CT media included 25:50:25, 25:25:50, and 50:25:25 CT:PS:PE, or 50:50 and 75:25 CT:PE.
Shoot dry weight of vinca and impatiens and stem diameter of vinca were greater for 25:50:25 CT:PS:PE than controls. Shoot dry weight and stem diameter of salvia were similar for CT media and controls. CT additions increased bulk density but decreased particle sizes, total porosity, and container capacity.
We conclude that CT-growing methodology could be implemented without loss of plant quality, although physical media characteristics limit the amount of compost and component ranges within container media.
Germination Responses of Purpletop and Big Bluestem Caryopses Subjected To Distilled Water or Potassium Nitrate Prechilling, Sodium Hypochlorite, and Storage(Publication: HortScience)
Purpletop [Tridens flavus (L.) Hitchc.] and big bluestem (Andropogon gerardii Vitman) are incorporated into native grass seed mixes for use in ecological restoration. Alleviation of low seed vigor and poor stand establishment would benefit the restoration process by increasing animal habitat in restored zones.
This study determined the effectiveness of prechilling with distilled water (dH2O) versus potassium nitrate (KNO3), sodium hypochlorite (NaOCl) treatments, and short-term storage conditions on seed germination, seedling growth, and stand establishment of purpletop and big bluestem. Prechilling of ‘Niagara, NY Ecotype’ big bluestem for 7 days at 5 oC in dH2O increased final germination percentage (FGP) and germination rate provided caryopses were not dried prior to sowing.
Optimal FGP, germination rate, and germination synchrony were obtained for ‘VA Ecotype’ purpletop following prechilling for 14 days at 5 oC in dH2O, without subsequent caryopsis drying, or at 0.2% KNO3 with or without subsequent caryopsis drying. Prechilling increased germination synchrony for purpletop but not for big bluestem. NaOCl treatments did not enhance germination or seedling vigor of purpletop or big bluestem.
Using nonstored, prechilled caryopses resulted in greater root lengths than stored caryopses or nontreated control, although optimal purpletop growth required that they be sowed moist while optimal big bluestem growth required that they be dried-back prior to sowing.
In greenhouse experiments, higher seeding rates were correlated with increased number of seedlings for nontreated or prechilled big bluestem and for prechilled purpletop, but not for nontreated purpletop which had poor stand establishment at all seeding rates. The results indicate that prechilling of caryopses prior to incorporation into a warm-season grass seed mix increased seedling establishment of purpletop but not big bluestem.
Assessment of Physical Properties and Stonecrop Growth in Two-Inch (Five-Centimeter) Depth Green Roof Substrates Amended with Compost and Hydrogel (manuscript/research currently under peer-review)
There is a lack of quantifiable data concerning physical analyses specific to shallow-depth green roof substrates and their effects on plant growth. Physical properties of substrates containing course slate (CS):fine slate (FS):compost (CT) at respective ratios of 70:30:0, 60:30:10, and 50:30:20 (%, by vol.), controlled release fertilizer, and 0 (control), 0.45, 0.90, or 2.25 kg·m-3 hydrogel, were determined and growth responses of stonecrop species (Sedum floriferum and S. spurium) assessed nine weeks after plug transplantation into 2-inch (5-cm) depth substrate.
Single degree of freedom contrasts indicated that shoot dry weight (SDW) and coverage area (CA) increased when substrates were amended with CT or 2.25 kg·m-3 hydrogel. Amendment with CT increased smaller particle sizes (< 0.50 mm) resulting in reduced aeration porosity (AP) and reduced aeration at applied suction pressure of 6.3 kPa (AP-6.3 kPa). Higher AP-6.3 kPa values for 0% CT control, but not 10 or 20% CT controls, indirectly suggested a reduction of capillary water, which is dependent on pore size distribution within substrates. Compared to their respective control, total porosity (TP) increased in all substrates following additions of 2.25 kg·m-3 hydrogel.
Container capacity (CC) was greatest in substrates containing 2.25 kg·m-3 hydrogel and/or hydrogel plus CT. Variations of initial and final pH and electrical conductivity (EC) were minimal but initial pH measurements were highest for 0% CT substrates.
We conclude that addition of CT and hydrogel amendments to slate-based substrates increased growth of S. floriferum and S. spurium concomitant with increased CC and related hydrological properties.