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Amy L. Shober, Geoffrey C. Denny and Timothy K. Broschat

Rapid population growth and urbanization in Florida have increased the number of urban landscapes that receive fertilization and irrigation. Consequently, maintenance of these landscapes may contribute to water shortages and water quality degradation. This article 1) describes the current fertilizer and water use practices that are used by homeowners and landscape professionals; 2) summarizes the research related to nutrient and water use by landscape plants; and 3) provides an overview of the critical issues that should be considered as we evaluate the need for improved management of water and nutrients in urban landscapes.

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Amy L. Shober, Andrew K. Koeser, Drew C. McLean, Gitta Hasing and Kimberly K. Moore

Several Florida cities and counties ban fertilization during the summer rainy season (fertilizer blackout). Little research is available to support or contradict the underlying justifications for these policies. We used large-volume lysimeters to address the impacts of several fertilization regimes on plant growth and aesthetics of sweet viburnum (Viburnum odoratissimum Ker Gawl.) and nitrogen (N) leaching from landscape beds during shrub establishment and maintenance. Three levels of N fertilization (98, 195, and 293 kg·ha−1), two levels of application method (per plant and broadcast), two levels of fertilization timing (regular and blackout), and an unfertilized control (0 kg·ha−1 N) were applied to lysimeters in a completely randomized design with three replicates (3 × 2 × 2 factorial plus untreated control). Increasing fertilization rate increased plant growth and improved plant quality, but also increased N leaching from lysimeters. Including a summer fertilization blackout period reduced nitrate + nitrite (NO3 + NO2-N) loading from lysimeters during sweet viburnum establishment [0 to 28 weeks after planting (WAP)] compared with year-round fertilization at the same total N rate without adversely impacting plant growth or aesthetics. However, NO3 + NO2-N loads from lysimeters were higher when fertilizers were applied on the summer blackout application schedule during the shrub maintenance period. Targeted (per plant) fertilization beneath the dripline of sweet viburnum at an annual N rate of 195 kg·ha−1 can maintain plant health while limiting N leaching losses on a year-round or blackout fertilization schedule.

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Kimberly A. Moore, Amy L. Shober, Gitta Hasing, Christine Wiese and Nancy G. West

Previous research indicated that acceptable quality annual and perennial plant species can be grown in the landscape with low nitrogen (N) inputs. However, information on the impact of soil conditions and N use by ornamental plants grown in central Florida is lacking in the literature. Our objective was to evaluate plant growth and quality response of eight warm-season annuals, seven cool-season annuals, and four herbaceous perennial species to a range of N fertilizer rates when plants were grown in landscape beds containing native field soil or subsoil fill. A slow-release N source (42N–0P–0K) was applied every 12 weeks at annual N rates of 3, 5, or 7 lb/1000 ft2 for a period of 18 weeks (annual species) or 1, 3, or 5 lb/1000 ft2 for a period of 54 weeks (perennial species). Plants were evaluated for aesthetic quality every 6 weeks and shoot dry weight was measured at completion of the experiment. Dry weight production and aesthetic quality of most species evaluated was unaffected by N rate. For several species, shoot dry weight was higher when planted in the field plots containing native soil [alyssum (Lobularia maritima) ‘Bada Bing White’ wax begonia (Begonia ×semperflorens-cultorum), dahlberg daisy (Thymophylla tenuiloba), ‘Survivor Hot Pink’ geranium (Pelargonium ×hortorum), gomphrena (Gomphrena globosa), ‘Blue Puffs Improved’ (‘Blue Danube’) ageratum (Ageratum houstonianum), blanket flower (Gaillardia pulchella), goldenrod (Solidago chapmanii), ‘Mystic Spires’ salvia (Salvia longispicata ×farinacea)]. Quality response to soil condition was mixed over the course of the study. Several species performed as well (or better) in the field as when planted in the subsoil fill soils. These results illustrate that some landscape plant species are able to survive and thrive under various soil and fertility conditions. These “tougher” species may be good choices for installation in landscapes with marginal native soils or disturbed urban landscape soils.

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Amy L. Shober, Christine Wiese, Geoffrey C. Denny, Craig D. Stanley, Brent K. Harbaugh and Jianjun Chen

Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat in Florida and other areas. The objectives of this study were to evaluate the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates on the growth of Solenostemon scutellarioides L. Codd ‘Wizard Velvet’, Tagetes patula L. ‘Safari Queen’, and Begonia ×hybrida ‘Dragon Wing Red’ and to examine the nutrient content in leachate from pots. Plants were grown for 5 weeks in a greenhouse in 15-cm plastic pots with seven substrates containing various proportions of sphagnum peat (S) or reed-sedge peat (R) and composted dairy manure solids (C), each with 20% vermiculite and 20% perlite. Substrate composition had no effect on plant quality ratings, number of flowers, or root dry mass for any of the plant species evaluated. Substrate composition did not affect the growth index (GI) or shoot dry mass of S. scutellarioides ‘Wizard Velvet’ or the GI of T. patula ‘Safari Queen’. However, growth of B. ×hybrida ‘Dragon Wing Red’ (GI and shoot dry mass) and T. patula ‘Safari Queen’ (shoot dry mass only) was highest in the 3S:0R:0C substrate. The substrates containing sphagnum peat and/or composted dairy manure solids (3S:0R:0C, 2S:0R:1C and 1S:0R:2C) had the highest NH4-N losses through the first 7 d of production. The 0S:3R:0C substrate had the highest initial leachate NO3+NO2-N losses and this trend persisted throughout most of the production cycle. Significantly more dissolved reactive phosphorus was leached from substrate mixes containing composted dairy manure solids than mixes containing only sphagnum or reed-sedge peat materials through 19 d after planting. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown bedding plant species based on plant growth and quality. However, nutrient losses from the containers differed depending on the peat or peat substitute used to formulate the substrates.

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Shawna Loper, Amy L. Shober, Christine Wiese, Geoffrey C. Denny, Craig D. Stanley and Edward F. Gilman

The urban soil environment is usually not conducive to healthy root growth and function, leading to problems with plant establishment, growth, and aesthetic quality. The objective of this study was to determine if the addition of compost with or without the application of shallow tillage or aeration will improve soil physical and chemical properties and plant growth compared with an unamended control in simulated new residential landscapes. Twenty-four mixed landscape plots were established in a randomized complete block design to simulate new residential landscapes. Each plot was constructed using 10 cm of subsoil fill material over a compacted field soil and planted with Stenotaphrum secundatum and mixed ornamental plant species. Composted dairy manure solids were applied as an organic soil amendment at a depth of 5 cm (≈256 Mg·ha−1) in combination with two mechanical soil treatments (tillage to 15 cm and plug aeration) for a total of five soil management treatments plus an untreated control. Soil physical and chemical properties, plant growth, and quality and plant tissue nutrient concentrations were assessed periodically to determine the effect of soil treatment on soil and plant quality. Applications of compost to soils significantly reduced soil bulk density and pH and increased soil organic matter, electrical conductivity, and Mehlich-1 phosphorus and potassium concentrations. All ornamental plant species, with the exception of Raphiolepis indica (L.) Lindl. ex Ker Gawl., exhibited more growth when grown in soils amended with composted dairy manure solids. In most instances, plant tissue nitrogen and phosphorus concentrations were higher for plants grown in soils receiving compost. Results of our study suggested that the addition of composted dairy manure solids to soils can improve soil properties and enhance plant growth in residential landscapes when sandy fill soils are used. In contrast, shallow tillage and aeration had little effect on soil properties or plant growth.

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Kimberly A. Moore, Amy L. Shober, Gitta S. Hasing, Christine L. Wiese, Geoffrey C. Denny and Gary W. Knox

Recent research suggested that the nitrogen (N) fertilizer rates needed to maintain high-quality landscape plants was lower than rates needed to grow the largest size plants. Our objective was to evaluate the effect of N fertilizer rate on the aesthetic quality of various landscape-grown annual and perennials species. Nineteen cool-season annuals, 20 warm-season annuals, and 4 perennials were planted into raised beds containing subsoil fill material in a completely randomized design in west-central Florida (U.S. Department of Agriculture hardiness zone 9b). Plants were fertilized every 12 weeks with polymer coated, slow-release N (42N–0P–0K) fertilizer at annual N rate of 3, 5, or 7 lb/1000 ft2 (annuals) or 1, 3, or 5 lb/1000 ft2 (perennials). Plants were rated for aesthetic quality every 6 weeks for a period of 18 weeks (annuals) or 54 weeks (perennials). For most species, quality ratings of plants fertilized with 3 lb/1000 ft2 of N per year (annuals) or 1 lb/1000 ft2 of N per year (perennials) were not significantly lower than plants receiving higher rates of N annually. Previously reported N fertilizer recommendations for central Florida of 2 to 4 lb/1000 ft2 per year should be adequate for maintaining acceptable quality landscape-grown annual and herbaceous perennial plant species.

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Amy L. Shober, Kimberly A. Moore, Gitta S. Hasing, Christine Wiese, Geoffrey C. Denny and Gary W. Knox

Research supporting recommendations for fertilizer needs of landscape-grown vines and groundcovers is lacking. The objectives of our study were to (1) evaluate the quality response of selected vine and groundcover species to nitrogen (N) fertilization at five rates and (2) validate the recommended N fertilizer rates (from the initial evaluation) by monitoring quality of additional landscape-grown vine and groundcover species. Three vine species and two groundcover species were planted in west-central Florida into raised beds containing subsoil fill material in a completely randomized design. Plants were fertilized every 6 weeks with a controlled release fertilizer (20N–0P–0K–23S) at an annual N rate of 0, 2, 4, 6, or 12 lb/1000 ft2. Plant aesthetic quality (0–5 scale) was assessed every 6 weeks for 30 weeks after planting. Although quality of some species increased significantly as N rate increased, all plants supplied with at least 4 lb/1000 ft2 per year N fertilizer had acceptable quality ratings of 3 or better. Screening of three additional vines and four additional groundcovers fertilized with controlled release fertilizer (42N–0P–0K) at an annual N rate of 3, 5, or 7 lb/1000 ft2 confirmed that fertilization with 2 to 4 lb/1000 ft2 per year should be adequate to maintain acceptable vines and groundcovers grown in the landscape in west-central Florida.

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Kimberly A. Moore, Amy L. Shober, Edward F. Gilman, Christine Wiese, S. Michelle Scheiber, Maria Paz and Meghan M. Brennan

The survival of shrubs planted into the landscape depends on sufficient irrigation during the establishment period. Few studies have investigated the effect of irrigation frequency on the posttransplant growth of landscape shrubs. We conducted two studies in U.S. Department of Agriculture hardiness zone 10b over a 2-year period in which we compared canopy growth index (GI), root extension to canopy spread ratio, canopy dry weight, and root dry weight of shrubs irrigated at different frequencies. In the first experiment, wild coffee (Psychotria nervosa) and ‘Lakeview’ orange jasmine (Murraya paniculata) shrubs were planted in Sept. 2004, Dec. 2004, Mar. 2005, and June 2005 and irrigated for 28 weeks after planting (WAP) every 2, 4, or 8 days with 3 L of water per irrigation event. In the second experiment, ‘Macafeeana’ copperleaf (Acalypha wilkesiana) and orange jasmine shrubs were planted in Sept. 2005, Dec. 2005, Mar. 2006, and June 2006 and irrigated for 28 WAP every 1, 2, or 4 days with 3 L of water per irrigation event. Canopy GI and root extension to canopy spread ratio were determined at 28, 52, and 104 WAP. The entire canopy and roots were harvested 52 and 104 WAP to determine dry weight. In Expt. 1, wild coffee and orange jasmine plants irrigated every 2 days had greater GI than plants irrigated every 8 days at 28 WAP, but GI was not different at 52 or 104 WAP. Canopy dry weight at 52 WAP was greater for plants irrigated every 2 days than every 8 days, but there was no difference at 104 WAP. There was no difference in wild coffee or orange jasmine root dry weight or root extension to canopy spread ratio among the irrigation frequencies. In Expt. 2, there were no differences in GI, canopy dry weight, root dry weight, or root extension to canopy spread ratio of copperleaf or orange jasmine irrigated everyday compared with plants irrigated every 2 or 4 days. From the data collected in these studies, it appears that irrigating wild coffee or orange jasmine every 8 days during the first 28 WAP limited canopy growth but not root development. However, after 52 WAP, rainfall events appeared to be sufficient to eliminate any initial effects from irrigation frequency. Our data suggest that wild coffee, orange jasmine, and copperleaf from 3-gal containers can be successfully established in the landscape when irrigated with 3 L of water every 4 days for the first 28 WAP.

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Amy L. Shober, Kimberly A. Moore, Nancy G. West, Christine Wiese, Gitta Hasing, Geoffrey Denny and Gary W. Knox

Despite inconsistent reports of nitrogen (N) fertilization response on growth of landscape-grown woody ornamentals, broad N fertilization recommendations exist in the literature. The objective of this research was to evaluate the growth and quality response of three landscape-grown woody shrub species to N fertilizer. Three ornamental shrub species, ‘Alba’ indian hawthorn (Raphiolepis indica), sweet viburnum (Viburnum odoratissimum), and ‘RADrazz’ (Knock Out™) rose (Rosa) were transplanted into field soils in central Florida (U.S. Department of Agriculture hardiness zone 9a). Controlled-release N fertilizer was applied at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2 for 100 weeks. Plant size index measurements, SPAD readings (a measure of greenness), and visual quality ratings were completed every month through 52 weeks after planting (WAP) and then every 3 months through 100 WAP. Plant tissue total Kjeldahl N (TKN) concentrations and shoot biomass were measured at 100 WAP. Results of regression analysis indicated little to no plant response (size index, biomass, SPAD) to N fertilizer rate. Shrub quality was acceptable for all species through 76 WAP regardless of the N fertilization rate. However, quality of rose and sweet viburnum fertilized with N at the low rates (<2 lb/1000 ft2) was less than acceptable (<3 out of 5) after 76 WAP. Results suggest that posttransplant applications of fertilizer may not increase plant growth, but that low-to-moderate levels of N fertilization (2 to 4 lb/1000 ft2 per year) may help plant maintain quality postestablishment.

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Gitta Shurberg, Amy L. Shober, Christine Wiese, Geoffrey Denny, Gary W. Knox, Kimberly A. Moore and Mihai C. Giurcanu

Current nitrogen (N) fertilizer recommendations for landscape-grown ornamentals are based on limited research. The objective of this research was to evaluate plant response of selected warm- and cool-season annuals to N fertilizer applied at five rates in the landscape. Three warm-season annual species [‘Profusion Cherry’ zinnia (Zinnia elegans ×angustifolia), ‘Cora White’ vinca (Catharanthus roseus), and ‘Golden Globe’ melampodium (Melampodium divaricatum)] and three cool-season annual species [‘Telstar Crimson’ dianthus (Dianthus chinensis), ‘Delta Pure Violet’ pansy (Viola wittrockiana), and ‘Montego Yellow’ snapdragon (Antirrhinum majus)] were transplanted into raised beds containing subsoil fill in U.S. Department of Agriculture (USDA) hardiness zone 9a. Slow-release N fertilizer was applied over an 18-week period at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2. Trials were replicated a second year. Plant size index (SI), tissue chlorophyll (SPAD), and plant quality were determined every 6 weeks. Shoot biomass and tissue total Kjeldahl N (TKN) were determined at 18 weeks. Regression analysis indicated that all species required N inputs at annual rates exceeding 8 lb/1000 ft2 to achieve maximum size, shoot biomass, or SPAD. However, acceptable quality plants were produced at much lower N rates. We suggest application of N fertilizer at a rate of 4 to 6 lb/1000 ft2 per year to landscape-grown annuals to maintain acceptable plant quality and growth. We expect fertilization at lower rates (based on aesthetics) can reduce the amount of fertilizer applied and the potential for nutrient losses in runoff or leachate. Future research should address N fertilization needs in higher fertility soils as well as the response of other plant species.