Induction of drought tolerance by paclobutrazol and irrigation deficit in Phillyrea angustifolia during the nursery period

Phillyrea angustifolia is a native Mediterranean species, which has recently been considered suitable for landscaping purposes. We hypothesize that hardening plants in the nursery could increase their tolerance of drought after transplanting. The effects of paclobutrazol (PBZ) and different irrigation regimes applied to seedlings planted in 4.5-L plastic pots were investigated. PBZ was applied as a substrate drench at 0 mL L⁻¹ (untreated control), 30 mL L⁻¹ and 40 mL L⁻¹ per plant and three drip irrigation treatments were used: I100, plants watered at water-holding capacity, I60, plants watered to 60% of I100, and I40, plants watered to 40% of I100. Plants were pot-grown in an unheated greenhouse near the Mediterranean coast of SE Spain. A reduction in plant height and stem diameter was observed one month after being drenched by PBZ. The irrigation regime significantly affected plant height after three months of cultivation and did not affect stem diameter during the nursery period. Significant interaction between the irrigation regime and PBZ dose was evident for plant height during the nursery period. I100 and untreated PBZ plants had the lowest stomata density. PBZ doses significantly reduced canopy weight and leaf area compared with the control. I60 plants showed the greatest leaf area and canopy dry weight, and the highest root length, dry weight, volume and number of forks. Both I60 and I40 treatments showed an equally high water use efficiency (WUE) (calculated as the total plant dry matter divided by the total amount of water supplied by the irrigation treatments). In general, PBZ induced a suite of morphological adaptations (increased root-to-shoot ratio and stomata density, decreased leaf area reduction, fine roots, etc.) that might allow the plants to tolerate drought after transplanting.     

Influence of water deficit and low air humidity in the nursery on survival of Rhamnus alaternus seedlings following planting

Summary

The effect of irrigation and air humidity on the water relations and root and shoot growth of Rhamnus alaternus L. during the nursery phase was considered to evaluate the resulting degree of hardening obtained by these treatments. R. alaternus seedlings were pot-grown in two greenhouses of equal characteristics. In one of these greenhouses air humidity was controlled using a dehumidifying system, while in the other one the environmental conditions were not artificially modified. In each greenhouse, two irrigation treatments were used. Thus, four different treatments were applied during the nursery phase (January-May): 1) control air humidity + control irrigation; 2) control air humidity + deficit irrigation; 3) low air humidity + control irrigation; 4) low air humidity + deficit irrigation. In May, plants of all treatments were transplanted and grown in good environmental and irrigation conditions for one month (17 May–20 June), after which they received no irrigation until the end of the experiment (14 July). Low air humidity and water deficit reduced all shoot growth parameters during the nursery phase, however the root growth was not significantly affected by air humidity and even increased under the water deficit. The reduction in leaf water potential under water stress was induced by tissue dehydration since leaf turgor potential also decreased and non-osmotic adjustment was observed. The drought effects on water relations were similar in both low and high air humidity. The leaf stomatal conductance was also reduced by both types of stress, leading to a decrease in the rate of photosynthesis at the end of the nursery phase. Both water deficit and low air humidity showed their value as nursery acclimation processes, improving the survival of seedlings following transplanting and non-irrigation conditions (establishment phase). The stomatal regulation and a shift in the allocation of assimilates from shoot to root were the acclimation mechanisms showed by R. alaternus under both types of stress. The accumulated effects in low air humidity and water deficit plants could explain the highest percentage of survival at the end of the establishment period (97%) for the combined treatment.     

Deficit irrigation as a strategy to control growth in ornamental plants and enhance their ability to adapt to drought conditions

The shortage of water in many parts of the world has led to the development of new irrigation strategies such as regulated deficit irrigation and sustained deficit irrigation. Water deficit induces different morphological and physiological responses in ornamental plants, but the application of irrigation strategies can obtain quality plants well adapted to the environment. Deficit irrigation controls plant growth, and can be considered a sustainable technique which avoids the use of plant growth regulators. In addition, root system morphology can be modified by water stress to improve the ability to extract water from the soil and strengthen a plant’s physical support. In addition, the application of deficit irrigation during nursery period is a technique frequently used to harden plants before transplanting. Water deficit affects morphological and physiological aspects that might provide a capacity to adapt to adverse conditions. All these features contribute to increasing water use efficiency and the root to shoot ratio and root density, promoting the more rapid establishment of ornamental plants in garden or landscape settings. In view of the results obtained, it is possible to apply and validate the most appropriate irrigation strategy for each species and to obtain the full benefits of applying deficit irrigation.

Abbreviations: DI, Deficit irrigation; ETc, Crop evapotranspiration; gs, stomatal conductance; Pn, Net photosynthesis; RDI, Regulated deficit irrigation; SLA, Specific leaf area; WUE, Water use efficiency     

The effects of irrigation on the establishment and yield of lettuce and leek transplants raised in peat blocks

The establishment and yield of lettuce and leeks were not reduced by transplanting dry (—0.06 to —0.09 MPa) as compared to saturated peat blocks (3.2 cm cube), provided irrigation was applied immediately after transplanting during the summer. When irrigation was withheld until eight days after transplanting the marketable yield of lettuce was reduced by 30% and 38% when transplanted in saturated and in dry blocks respectively. These reductions were due to reduced survival during establishment and to the more extensive trimming required to produce marketable heads rather than to a reduction in total fresh weight per plant at maturity. The marketable yield of leeks was reduced by 16% and 24% when saturated and dry blocks respectively were transplanted without irrigation, the reduction being largely due to a lower mean shoot weight. Measurements of block and soil water after transplanting suggested that even when the soil was irrigated immediately after transplanting, it was urmble to supply water directly to the blocks for more than a few days.     

Responses of morphology and drought tolerance of Sedum lineare to watering regime in green roof system: A root perspective

The presence of drought tolerant vegetation is essential for the longevity of an extensive green roof when irrigation is not installed. Earlier studies have examined performance of green roof plants under contrasting watering regimes and found that higher watering frequency provided better growth and survival rates. The effect of early watering regimes on the subsequent response of plants to persistent drought stress in extensive green roofs, however, has not been extensively studied. In order to evaluate the effects of watering regime during the establishment period of Sedum lineare on its growth and drought tolerance, two greenhouse experiments using simulated green roofs were conducted. It was found in the first experiment that a 2-day-interval watering regimen at the early planting stage produced greater root biomass and root size than those of 6-day- and 13-day-interval watering, indicating that deficit watering tended to induce thinner roots in S. lineare. In the second experiment, the remaining plants were subsequently subjected to a 28-day drought treatment. The roots of plants watered at 13-day-interval maintained the highest respiration activity among all plants during the drought period. Results suggest that an appropriate deficit watering regimen at the early planting stage may lead to smaller root size and higher root:shoot ratios in S. lineare, and thereby improve its drought tolerance performance on extensive green roofs.     

Synchronization of anthesis and enhancement of vegetative growth in coffee (Coffea arabica L.) following water stress during floral initiation

SUMMARY

The possibility of using water stress during floral initiation and development, to synchronize flowering in potted coffee trees of cvs Catuai Rojo and Mundo Novo was investigated. Moderate and severe cyclic and constant water stress had little effect on vegetative growth during floral initiation. However, upon rewatering, shoot growth was significantly greater in plants where leaf water potential [¨,] had declined to -2.5 MPa compared with plants where ¨, was maintained above -0.5 MPa. The period of floral initiation was not influenced by water stress and occurred only under short days (<12 h). In contrast, a y, of -2.5 MPa significantly reduced the number of inflorescences compared with plants maintained at a ¨| of -0.5 or -1.5 MPa. This reduction was associated with leaf drop in stressed plants. Therefore, regular irrigation during the period of floral initiation is recommended. Water stress (¨, of -1.5 or -2.5 MPa compared with -0.5 MPa) accelerated floral development with no deleterious effects on floral differentiation. Once flower buds are fully differentiated they enter dormancy and reach anthesis only if trees are stressed and rewa-tered. Flower buds remain dormant if trees are watered regularly or a constant water stress provided. A constant period of water stress in the late stages of floral development after floral initiation is complete provides a means of increasing the proportion of fully differentiated dormant flower buds (mature buds). This could represent a practical method to achieve synchronized flowering in field conditions where there is irrigation and a reliable dry season in the late stages of floral development.     

Estimation of relative water use among ornamental landscape species

Low water use plantings may enhance water conservation in dry landscapes. However, appropriate plant selection is hindered by the dearth of information available on the water needs of different species. A direct method of classification was tested under the hypothesis that relative water use by woody landscape species growing in 3.8 l containers would be representative of the water use of the same species in the landscape. Four species of distinctly different ecological origin (Leucophyllum frutescens, Spiraea vanhouteii, Viburnum tinus, Arctostaphylos densiflora) were chosen in order to obtain a wide range of responses, and their water use was measured in plants growing in 3.8 l containers and compared to that of the same species growing in drainage lysimeters, representative of landscape conditions. Half of the plants were subjected to successive cycles of stress by withholding water after irrigation to container capacity in containers, or applying a fraction of the potential evapotranspiration in lysimeters. The good fit of the regression of average daily water use by lysimeter plants on average daily water use by container plants (R²=0.87,P<0.01) reflects the consistency of relative water use of the four species. Measurement of water use at the end of nursery production may be useful for predicting the relative water use of various species after establishment in the landscape.     

Response of container-grown photinia to moisture stress

Two experiments were conducted to determine the effect of Vapor Gard (VG), an antitranspirant, and moisture stress on shoot water potential of container-grown photinia. In Experiment 1, plants sprayed with VG has less moisture stress than plants with no VG when 24.0 and 27.5 mm of net evaporation occurred prior to watering. Recovery periods for shoot water potential were within 4, 8 and 24 h for photinia stressed to 21.5, 24.0 and 27.5 mm of net evaporation, respectively. Photinia with and without VG were compared in Experiment 2. Shoot water potential and stomatal opening were measured pre-dawn daily (for 9 days) on photinia stressed to ?25 and ?35 bars pre-dawn shoot water potential before watering. Plants watered daily had a maximum pre-dawn shoot water potential of ?3 bars, and watered plants had a higher shoot water potential than stressed plants. Within 8 h after watering, plants with a pre-dawn stress of ?25 bars recovered to shoot water potentials of plants watered daily, and stomates closed regardless of VG treatment. Pre-dawn stress to ?35 bars resulted in a longer recovery period of shoot water potential (about 36 h). Stomates were closed on plants treated with VG and open on plants not treated with VG. Defoliation (25–75%) occurred on plants stressed to ?35 bars and not treated with VG.     

CCROP—Simulation model for container-grown nursery plant production

Container Crop Resource Optimization Program (CCROP) is an integrative model which simulates the growth and water and nutrient requirements of a woody ornamental shrub grown in small (2.8–11.4 L) containers in a field environment with overhead sprinkler irrigation. The model was developed for producers, producer advisers and researchers to support best management practice decision-making in container nursery production. We describe the primary processes simulated by CCROP particularly how they differ from traditional crops grown in-ground and assess the ability of CCROP to simulate measured values for a range of irrigation and fertilizer trials and transplanting dates. Results of model testing with 11 trials indicate that CCROP provided reasonable outcomes for biomass and leaf area growth as well as evapotranspiration, runoff (container drainage plus un-intercepted irrigation and rainfall) and nitrogen loss.     

Methods of Raising Cocoa Seedlings in the Nursery and their Effect on Subsequent Growth in the Field

Trials were conducted near Ibadan, Western Nigeria, to find the best method of raising cocoa seedlings in the nursery, and the plants were subsequently transplanted to the field and observed for two further years. In one trial the experimental treatments were amount of shade, time of sowing, amount of watering and type of pot; in a second trial times of sowing and transplanting were varied and seed was also sown at its permanent site.

Seedlings grew well in the nursery in polythene pots under a shade of from eight to ten palm fronds per 10 ft. length and with light watering. Late sowing and early transplanting were satisfactory, so seedlings need only remain in the nursery for five or six months; in the Ibadan area this was achieved by sowing in December and transplanting in late Mayor early June. Younger plants also grow well in the field, but there are risks in sowing seed in January, when cold, dry harmattan winds may be expected. Provided a plant is big enough to transplant, its original size has no bearing on its subsequent growth in the field, as measured by trunk girth at threemonthly intervals. Sowing seed at permanent sites is risky, as beans may be eaten by rodents.     

Growth of Betula pendula Roth. the first season after transplanting at two phenological stages

The root extension rate of Betula pendula, transplanted at two phenological stages, was studied in a Nordic climate. Landscape-size trees were transplanted from the field into root-study boxes (rhizotron) in early and late spring of 1999 and 2000. In early spring, 6 trees were transplanted when the leaves had just started to unfold; likewise, in late spring, six trees were transplanted when the leaves were fully unfolded and the shoot extension was in progress. Root growth was recorded during the first post-transplant season and the tree roots were finally excavated. Results indicate that the root extension rate of B. pendula follows seasonal soil temperature. The mean root extension rates at ten days intervals varied from 4 to 11 mm/day with a total average for the growing season of 7 mm/day in 1999 and varied from 4 to 9 mm/day with a total average for the growing season of 4 mm/day for 2000. The average length of new roots was 89 cm and there was no significant difference in length, dry weight or number of new roots between the two transplant times. It appears, therefore, that the phenological stage at transplanting during the period from bud break to fully developed leaves has minor effect on landscape establishment of B. pendula, when an adequate amount of water is provided.     

Comparative effects of deficit irrigation (DI) and partial rootzone drying (PRD) on soil water distribution,water use,growth and yield in greenhouse grown hot pepper

This study was conducted to compare two water-saving practices, deficit irrigation (DI) and partial rootzone drying (PRD), and examine how they affected soil water distribution, water use, growth and yield of greenhouse grown hot pepper compared to commercial irrigation (CI). Control (CI) in which irrigation water was applied to both sides of the system when soil water content was lower by 80% of field capacity; deficit irrigation (DI50, DI75) in which 50% and 75% irrigation water of CI supplied to both sides of the root system; 1PRD with half of the root system exposed to soil drying and other half kept well-watered with 50% irrigation water of CI, and 2PRD with 50% irrigation water of CI supplied, half to fixed side of the root system. The results showed mean soil volumetric water content of DI75, DI50, 1PRD and 2PRD were lower by 21.06%, 28.32%, 24.48% and 34.76%, respectively than that of CI after starting the experiment. Water consumption showed some significant effect of irrigation treatments during the growing period of drought stress application, and therefore decreased in DI75, DI50, 1PRD and 2PRD to a level around 75% and 50% of CI. All the DI and PRD treatments resulted in a reduction of total dry mass of 7.29–44.10%, shoot biomass of 24.97–47.72% compared to CI, but an increase in the root–shoot ratio of 12.50–35.42% compared to the control and with significant differences between 2PRD, 1PRD, DI50 and CI. The yield of 1PRD was significantly reduced by 23.98% compared to CI (19,566 kg hm⁻²) over a period of 109 days after transplanting. However, the 1PRD treatment had 17.21% and 24.54% additional yield over the DI50 and 2PRD treatments and had 52.05% higher irrigation water use efficiency (IWUE) than CI treatment. At harvest, although there was a significant difference recorded as single fruit weight and single fruit volume were reduced under the DI and PRD treatments, total soluble solids concentration of fruit harvested under the water-deficit treatments were higher compared to CI. Stomatal conductance measured in fresh leaf was the lowest under 1PRD treatment relative to CI and other treatments. The low stomatal conductance of fresh-leaf issue observed in the work supported the root signaling mechanism reported earlier in plants having undergone partial root drying cycles.     

日光温室冬春茬黄瓜产量与灌水量的关系

对华北地区日光温室冬春茬黄瓜产量与灌水量的关系进行了研究,黄瓜于１１月２５日播种,翌年１月１０日定植,从定植到拉秧１４０ｄ（天）,设５个灌水量处理（１６２．５～４８４．１ｍ３·６６７ｍ－２）。结果表明,黄瓜产量（９１９２～１２９３３ｋｇ·６６７ｍ－２）随灌水量的增加而增加,灌水利用效率则随之减少,黄瓜品质有下降的趋势。利用含盐量２．２ｇ·Ｌ－１微咸水灌溉,土壤盐分累积显著,但土壤表层盐分随灌水量的增加而减少。     

Evaluating variability of root size system and its constitutive traits in hot pepper (Capsicum annum L.) under water stress

The importance of root size system has long been recognized as crucial to cope with drought conditions. This investigation was conducted to: (i) evaluate the variability in root size system of hot pepper at maturity; (ii) estimate the effect of root size system on yield under drought conditions; and (iii) effect of water stress on xylem vessel development and total xylem cross-sectional area in roots of hot pepper cultivars. Twelve diverse hot pepper cultivars were grown in wooden boxes with two different water treatments, normal and in 50% water application as water deficit condition. Mean primary root length (PRL) showed a significant positive correlation with final fruit yield at normal as well as stressed condition. Total dry mass of fruit was reduced by 34.7% in drought treatments (DI) compared to full watered treatment (FI). At harvest, water-stressed plants had 21% lower root dry weight mass but higher root:shoot ratio other than FI. PRL, lateral root density, total xylem area per root cross-section showed a significant positive relationship with fruit yield. Also, lateral root density was higher in cultivars with higher xylem density, particularly in tolerant cultivars. Lateral root density (r = 0.847, P < 0.001) and total xylem cross-sectional area in root (r = 0.926, P < 0.001) were tightly related with total biomass production. The importance of root traits contributing to withstand drought in hot pepper is discussed.     

Mycorrhizal colonization improves onion (Allium cepa L.) yield and water use efficiency under water deficit condition

Most plants benefit from mycorrhizal symbiosis through improvement of water status and nutrient uptake. A factorial experiment with complete randomized blocks design was carried out in greenhouse at Tabriz University, Iran in 2005–2006. Experimental treatments were (a) irrigation interval (7, 9 and 11 days), (b) soil condition (sterile and non-sterile) and (c) arbuscular mycorrhizal fungi (AMF) species (Glomus versiforme, Glomus intraradices, Glomus etunicatum) and non-mycorrhizal (NM) plants as control. Onion (Allium cepa L. cv. Azar-shahr) seeds were sown in sterile nursery and inoculated with fungi species. One nursery left uninoculated as control. Nine weeks old seedlings then were transplanted to the pots. Average pre-irrigation soil water contents reached to about 67, 61.6 and 57.5% of FC corresponding to 7, 9 and 11 days irrigation intervals, respectively. At onion bulb maturity stage (192 days after transplanting), yield, water use efficiency (WUE) and yield response factor (K_y) were determined. The results indicated that AMF colonization increased soil water depletion significantly. G. versiforme under both soil conditions (sterile and non-sterile) and G. etunicatum in sterile soil depleted soil water effectively (P < 0.05). Mycorrhizal fungi improved WUE significantly (P < 0.0001) in both soil conditions. It raised by G. versiforme about 2.4-fold (0.289 g mm⁻¹) in comparison with the control (0.117 g mm⁻¹). G. intraradices and G. etunicatum also had significantly higher WUE than control. Apparently water deficit in 11-day irrigation interval led to lower yield and WUE compared to 9-day interval; the later resulted highest WUE (0.254 g mm⁻¹). Mycorrhizal plants increased seasonal ET significantly due to enhancing in plant growth; G. versiforme in both sterile and non-sterile soil and G. etunicatum in sterile soil had the highest ET. Bulb yield was influenced by irrigation period and fungi species. G. versiforme produced higher yield than other treatments (135.27 g/pot). Mycorrhizal plants in 11-day irrigation interval in spite of suffering from water stress had more bulb yield than non-mycorrhizal plants in all irrigation intervals. Yield in general was higher in 9-day treatments than other irrigating internals significantly (P < 0.05). Onion yield response factor (K_y) was decreased by AMF colonization; implying that symbiosed plants become less responsive to water deficit (longer irrigation interval) compared to the control ones.     

Water relations of coffee leaves (Coffea arabica and C. canephora) in response to drought

Coffee plants of five Arabica and one Canephora genotypes were raised in containers with 0.02 nr1 of soil, under a clear plastic shelter. When they were 18 months old, irrigation was withheld until the first signs of wilting appeared. This occurred four to five days after withholding irrigation, when the pre-dawn water potential of young fully expanded leaves of the plagiotropic branches was about -2.4 MPa. Control plants remained under daily irrigation. The pressure-volume technique was used to estimate volume averaged water relations properties of sample leaves. The turgor loss point was approximately -1.6 MPa for control plants and -2.0 MPa for stressed plants, an osmotic adjustment of approximately 22%. The Canephora genotype showed a slightly higher adjustment. The relative water content at the turgor loss point remained at approximately 93%, irrespective of genotype or treatment. The maximum bulk modulus of elasticity did not change significantly with water deficit, remaining at about 24 MPa, except for a slight increase in the Canephora genotype. The specific leaf area of the Arabica genotypes decreased about 20%, as compared with a 10% decrease for the Canephora genotype.     

An improved water use efficiency for hot pepper grown under controlled alternate drip irrigation on partial roots

Hot pepper plants were grown in pots with their roots divided and established in two separate containers. Water was applied through a drip irrigation system in three ways: alternate drip irrigation on partial roots (ADIP), fixed drip irrigation on partial roots (FDIP), even drip irrigation on whole roots (EDIW). For each irrigation method, water was applied when the soil moisture content was below either 65 or 55% of the field capacity. Results showed that when irrigation started at 65% of the field capacity ADIP significantly increased the root/shoot ratio compared to all the other treatments. When irrigating at this moderate (i.e. 65% of the field capacity) soil moisture level, ADIP did not significantly inhibit leaf photosynthesis, but did markedly restrict stomatal opening. Compared to EDIW, there was a relatively small reduction in biomass for ADIP, but the reduction for FDIP was significant. Surprisingly, ADIP maintained high yield with up to 40% reduction in irrigation compared to EDIW and FDIP. Moreover, the maximum yields and best water use efficiency occurred in ADIP and rewatering at 65% level at the same time. FDIP did not show better results than the controls because the yield was considerably reduced. In conclusion, ADIP is an effective and water-saving irrigation method in hot pepper production and may have the potential to be used in the field.     

Root and shoot growth of newly-transplanted apple trees as affected by rootstock cultivar,defoliation and time after transplanting

Summary

An experiment with Malus demonstrated that a large proportion of the transplanted root system was lost through death and decomposition soon after transplanting in the open ground. Mortality of the roots was not influenced by the rootstock cultivars or by defoliation but increased significantly with time. In the first month, shoots of maiden trees of Malus transplanted in June when in-leaf grew, but roots did not. Subsequently, most of the new roots on the rootstock M.9 regenerated from the rootstock stem, whereas with MM.106 the old coarse roots (>2.0 mm diameter) initially present at planting were most important. Root growth occurred in concert with shoot growth such that a functional balance was maintained as shown by the existence of a constant root length:leaf area ratio over a large part of the growing season. Following transplanting, the trees appear to re-establish their optimal ‘functional’ ratio by way of a co-ordinating pattern of growth tending to correct any disturbance to the ratio resulting from transplanting. Defoliation in the early establishment phase caused only a temporary initial reduction in the root growth, but reduced all the shoot growth variables measured and increased the root length:leaf area ratio throughout the growing season.     

Irrigation of Myrtus communis plants with reclaimed water: morphological and physiological responses to different levels of salinity

Summary

The influence of irrigation with different sources of reclaimed water on physiological and morphological changes in Myrtus communis plants was investigated to evaluate their adaptability to such conditions. M. communis plants, growing in a growth chamber, were subjected to four irrigation treatments over 4 months (120 d): a control [tap water (0.8 dS m^–1), leaching 10% (v/v) of the applied water] and three reclaimed water irrigation treatments, namely 1.5 dS m^–1 leaching 25% (v/v) of the applied water (RW1), 4.0 dS m^–1 leaching 40% (v/v) of the applied water (RW2), and 8.0 dS m^–1 leaching 55% (v/v) of the applied water (RW3). After treatment, all plants were irrigated with tap water, as for the control plants, for a further 2 months (60 d). At the end of the first period (4 months), none of the myrtle plants showed any adverse change in biomass and the average total dry weight (DW) increased by 53% in treatment RW2. However, at the end of the treatment and recovery period (180 d), accumulations of Cl^– ions, and especially Na⁺ ions, negatively affected the growth of all RW3 plants. Plants irrigated with all three reclaimed water samples had increased difficulty in taking-up water from the substrate (i.e., they had lower leaf water potential and relative water content values). RW2 plants showed a better response in their gas exchange parameters. The use of reclaimed water decreased leaf K⁺/Na⁺ and Ca²⁺/Na⁺ ratios, but no chlorosis or necrosis were observed. The three reclaimed water samples had different effects on the myrtle plants depending on the specific chemical properties of the water. Leaching was found to be important to minimise the negative effects of salinity in the irrigation water.     

Drought responses of six ornamental herbaceous perennials

Although low water use landscaping is becoming common in arid regions, little is known about drought tolerance and drought responses of many ornamental plants, especially herbaceous perennials. Drought responses were assessed for six herbaceous ornamental landscape perennials in a 38 l pot-in-pot system in northern Utah over a 2-year period. The first year was an establishment period. During the second year, drought responses were evaluated for established Echinacea purpurea (L.) Moench, Gaillardia aristata Pursh, Lavandula angustifolia P. Mill., Leucanthemum × superbum (J.W. Ingram) Berg. ex Kent, ‘Alaska’, Penstemon barbatus Roth var. praecox nanus rondo, and Penstemon × mexicali Mitch. ‘Red Rocks’. Plants were irrigated at frequencies of 1 (control), 2, or 4 weeks between June and September, simulating well-watered conditions, moderate drought, or severe drought. Osmotic potential (Ψ_s), gas exchange, visual quality, leaf area, and dry weight were assessed. In a confined root zone, P. barbatus showed the greatest tolerance to all levels of drought, avoiding desiccation by increasing root:shoot ratio and decreasing stomatal conductance as water became limiting. L. angustifolia and P. × mexicali showed tolerance to moderate drought conditions, but died after exposure to the first episode of severe drought. Neither G. aristata nor L. superbum were able to regulate shoot water loss effectively. Instead, both species displayed drought avoidance mechanisms, dying back when water was limiting and showing new growth after they were watered. Compared to control plants, G. aristata shoot dry weight was reduced by 50% and 84%, and L. superbum shoot dry weight was reduced by 47% and 99% for the 2- and 4-week irrigation intervals, respectively. Root dry weights were affected similarly for both species. E. purpurea exhibited poor visual quality at all irrigation intervals, in particular wilting severely in both drought treatments, but regaining turgor when watered again. P. barbatus is recommended for ornamental landscapes that receive little or no supplemental irrigation, while E. purpurea is not recommended for low water landscapes because of low visual quality under even mild drought.