Information on industrial hemp (Cannabis sativa) water use and water stress is sparse. We studied water stress impact in two essential-oil hemp cultivars (‘Wife’ and ‘Cherry’) prompted by anecdotal differences in growth and water use. In a greenhouse setting, we measured water relations, water use, growth, and essential oil (CBD-cannabidiol and THC-delta-9 tetrahydrocannabinol) concentrations. Water stress did not significantly affect THC and CBD concentrations, but both cultivars responded to water stress by reducing transpiration through notably different mechanisms. ‘Cherry’ had more anisohydric behavior, maintaining high stomatal conductance (Gs) and more negative leaf water potential until root zone water depletion triggered partial afternoon stomatal closure to moderate stress, resulting in lower flower and CBD yield. By contrast, water-stressed ‘Wife’ rapidly defoliated half its leaf area in balance with less applied water and so maintained high Gs and flower yield on par with well-watered plants, suggesting potential for deficit irrigation to conserve water and reduce post-harvest vegetation management. Differences in water use translated to provisionally suggested crop coefficients of 1 for ‘Cherry’ and 1.3–1.5 for ‘Wife’, but further research is needed. Because hemp is genetically diverse, and cultivar naming conventions are currently lax, further germplasm screening and research are needed to determine the extent to which either conservative ‘Cherry’ or the water-stress defoliation response of ‘Wife’ is found in the larger population of hemp cultivars.

We present the results of classifying plants at species level that can tolerate air pollution, provide cooling, and simultaneously survive and thrive in urban environments. For this purpose, we estimated the air pollution tolerance index (APTI) and anticipated performance index (API) of several species growing in a park located in central Bangkok, Thailand. The cooling effect was quantified by calculating the reduction in soil and air temperatures. Melaleuca quinquenervia (Cav.) S.T. Blake, Albizia saman (Jacq.) Merr., Chukrasia tabularis A. Juss. had the highest API score and were able to substantially reduce the temperature and were in a group of highly recommended species which also included other species like A. saman, C. tabularis, Tabebuia rosea (Bertol.) Bertero ex A. DC., Dalbergia cochinchinensis Pierre etc. Species from both evergreen and deciduous habitat were able to provide ambient cooling but were vulnerable to air pollution and included Elaeocarpus grandifloras Sm. and Bauhinia purpurea L. However, there were other species which had a high air pollution tolerance but failed to provide adequate cooling, such as Hopea odorata Roxb. and Millingtonia hortensis L.f. The results would be of interest to urban greenspace landscapers in such climates while selecting suitable species that can provide multiple ecosystem services ranging from air pollution tolerance to temperature reduction without reducing plant vitality.

Container crop production has become increasingly popular, but daily water requirements of those crops from transplanting to marketable or harvestable stages are largely unavailable. To address this concern, daily water consumption of two container-grown fern species, Davallia bullata and Nephrolepis exaltata from initial transplanting to marketable size were studied using a canopy closure model. Daily actual evapotranspiration (ET_A) of D. bullata ranged from 4.6 mL to 76.5 mL with an average of 29.0 mL per plant per day. The mean cumulative ET_A was 13.2 L during 431 days of production spanning from 8 November 2006 to 4 February 2008. Two crops of N. exaltata were produced. Daily ET_A per N. exaltata plant produced in crop 1 varied from 19.0 to 241.2 mL with an average of 69.5 mL, and daily ET_A of crop 2 differed from 5.7 to 136.8 mL with a mean of 74.0 mL. Both crops had a cumulative ET_A of 9.4 L. Such differences in daily ET_A and cumulative ET_A between the two fern species raised further concern of irrigation practices in commercial foliage plant production as multiple species are commonly produced in one greenhouse and share the same irrigation schedule. Comparing daily ET_A and cumulative ET_A values of the ferns with the other studied foliage plants indicated that daily ET_A and cumulative ET_A are species specific. Therefore, to improve irrigation efficiency, daily ET_A and cumulative ET_A values of major container-grown plants should be established. Implementing the research-based daily ET_A and cumulative ET_A in container plant production should reduce irrigation water leaching and runoff and conserving freshwater resources.

To meet minimum spring flows, water management districts in Florida sought to make both agriculture and urban landscapes water efficient, which includes tree farms. Ilex spp. (holly) trees are endemic to Central Florida and among the most popular landscape trees for their hardness, bright colors and go-anywhere size. To provide a basis for irrigation allocations both during production and in landscapes, daily actual evapotranspiration (ET_A) for three holly trees were measured with weighing lysimeters over 5.75 years, beginning with rooted cuttings and continuing until trees averaged 4.3 meters in height. Empirical models were derived to calculate ET_A based on crown horizontal projected area or trunk caliper, adjusted daily by changes in evapotranspiration (ETo). Average ET_A to produce these hollies was 20 432 L cumulative over 5.75 years.

We investigated seasonal water use, growth and acceptable root-zone water depletion levels to develop tools for the more precise irrigation of two Southeast U.S. landscape species in a monsoonal climate—Magnolia grandiflora and Viburnum odoratissimum. The study was conducted under a rainout shelter consisting of two concurrent studies. One, weighing lysimeter readings of quantified water use (ET_A) at different levels of irrigation frequency that dried the root zone to different allowable depletion levels (ADL). Two, planting the same species and sizes inground and irrigating them to the same ADLs to assess the effect of root-zone water depletion on growth. The projected crown area (PCA) and crown volume were concurrently measured every three weeks in both studies as well as reference evapotranspiration (ETo). Plant factor values were calculated from the ratio of ET_A (normalized to depth units by PCA) to ETo. The two species had different tolerances for irrigation frequency depending on the season: peak magnolia canopy growth was mid-spring to mid-summer, while peak viburnum canopy growth was summer. Canopy growth for both species was most sensitive to greater ADL-water stress during the peak growth stages of both species. For urban landscape irrigation, these data suggest that 60–75% of available water in magnolia and viburnum root zones can be depleted before irrigation and that they can be irrigated at a plant factor (PF) value of 0.6 of ETo. For landscape situations with high expectations, such as during establishment and especially during peak growth, a wetter water budget that minimizes water stress would be more appropriate: 30–45% ADL and PF values of 0.7–0.8. The results of this study are aimed at water managers and landscape architects and designers in a humid climate who need to account for water demand in planning scenarios.