Optimizing the Visual Quality and Cost Effectiveness of Perennial Plantings by Randomly Mixed Combinations-Application Approaches for Planting Design, W KIRCHER, U MESSER, J FENZL

Tags: Perennial Plantings, Planting Design, perennials, mixture, Campanula persicifolia, Dictamnus albus, mixtures, species, Wolfram Kircher, Cost Effectiveness, plant list, Jessica Fenzl, the University of Sheffield, color combinations, The Research Project, Lehr- und Versuchsanstalt, shady conditions, Herbaceous Perennial, FENZL & KIRCHER, Bernburg Experiments, public green spaces, dominant species, woodland habitats, ground cover plants, Angewandte Wissenschaften Institut Umwelt, Committee of Planting Design, visual display, German Research Foundation, Rudolf Goethe, planting strategy, core groups, plant combinations, Allium aflatunense, Aster amellus, distribution pattern, Carex montana, mixed strategy, Schau- und Sichtungsgarten Hermannshof, the German Perennial Nurseries Association, Research Institutions, Anhalt University of Applied Sciences, Anhalt University, Allium sphaerocephalon, Thymus serpyllum, core group, Material & Methods
Content: Optimizing the Visual Quality and Cost Effectiveness of Perennial Plantings by Randomly Mixed Combinations - Application Approaches for Planting Design. Wolfram KIRCHER, Uwe MESSER, Jessica FENZL, Marcel HEINS & Nigel DUNNETT 1 Introduction The planning of diverse and species rich perennial plantings is very time consuming. To increase the efficiency of the PLANNING PROCESS the concept of randomly mixed plantings was developed in a series of trials at Anhalt University of Applied Sciences, Bernburg, Germany. Compared with plantings based on a graphically depicted planting plan the visual quality of a mixed model was assessed equally ranking. 1.1 Planning of Perennial Plantings ­ Common Approaches of Planning Perennial Plantings Monoplanting: One simple and popular strategy in public green spaces is planting with a single species. Among the typical perennials used in monoplantings are competitive species of Geranium, Salvia, Lavandula, etc. Monoplantings are less cost intensive to planning, construction of the planting and maintenance as long as hardy and long lived perennials are used. Monoplantings are monotonous, since blooming occurs only for a certain period or even not at all. Evergreen shrubs such as Cotoneaster and Lonicera pileata do not show the seasonal changes typical to perennials and Deciduous trees and shrubs. Planting in groups or blocks (Fig. 1), usually of more than two different species, are another way of creating public green spaces. Block planting is essentially a more complex version of the above and is perhaps the most common approach to landscape planting (DUNNETT, KIRCHER, KINGSBURY 2004, p. 246). Block plantings consist of several different species planted for effect in groups of three to five or even more than one hundred. Block plantings can be subdivided into so-called drifts, which are strips, usually linear and at tendentially right angles to the observer, in order to provide perspective. Drifts contain groups of plants arranged in extremely narrow rows running more or less parallel to the main direction of the bed. This arrangement enhances the depth effect, but is more expensive to plan and maintain. Drift planting was used with great skill by Gertrude Jekyll in herbaceous and mixed borders. As a big advantage of this method ROBINSON (1998) mentions that the narrow groups would look best at their peak but also that they would not detract from the border after fading.
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Randomly Mixed Combinations - Application Approaches for Planting Design.
Fig. 1: Planting Plan arranged in groups
Fig. 2: Planting Plan arranged according to sociability levels
Planting according to sociability levels (Fig. 2): A very naturalistic approach is to arrange plants according to sociability levels I to V (according to Hansen & Stahl 1993). This planting strategy is applicable to perennials with a more "wildlife" effect. Plants of low sociability levels (groups I and II) are set individually or in small groups of three to nine. Plants of higher sociability levels (groups III to V) are set in groups of 10 to 20 or more and arranged loosely around those of groups I and II (Hansen & Stahl 1993).
1.2 Randomly Mixed Planting This approach aims to completely abstain from a drawn planting plan. Species and variety are carefully selected according to their habitat, competitiveness, flowering, height, and reproductive behaviour. The amount of each type of plant to be used is recorded according to these criteria in a list. By laying out the plants are distributed as evenly as possible over the entire area, starting with the species present in the lowest amounts. The exact position of every plant is not predetermined in a planting plan, but determined by chance. This planting strategy gives a natural effect. The idea behind this strategy is to create a plant community in an ecologically sound, competitive balance, comprising the ideal type of vegetation for public green spaces. Ideally, species showing various striking aspects, forms, heights and propagation strategies complement each other to form a self-regulating system. Within this dynamic model the survival of the entire planting under extensive maintenance is more important than survival of individual plants. The conditions at individual sites result in different competitive conditions and vegetation patterns despite identical plant components. Moreover, there are possibilities for introducing structure such as dominant visual elements or rather theme plants (especially "Dominant species" ­ see table 1; definition following BORCHARDT, 2006, complemented)
The term "Staudenmischpflanzung" (mixed perennial planting) was coined in 1994 by KOLB and KIRCHER at the Institute "Landesanstalt fьr Weinbau und Gartenbau" (LWG), Veitshцchheim, Germany. They were seeking to develop a simplified version of the concept of sociability levels (HANSEN & STAHL 1993), which would be practically applicable by inexperienced workers, who had never before worked with herbaceous perennial plantings. It is not necessary to have a planting plan with a list of the prescribed numbers of the plants to be used (KIRCHER 2000). In times of limited public funding the
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
concept of mixed herbaceous perennial planting is a reasonable way nevertheless to provide public green spaces as an alternative to costlier approaches with intricate planting plans or rather seasonal bedding.
2 Material & Methods
2.1 The Research Project "Mixed Herbaceous Perennial Planting" at Anhalt University, Bernburg Experiments to create suitable perennial mixtures as well as establishing and maintaining methods are carried out since 1999 at Anhalt University of Applied Sciences in Bernburg. This dry region provides an annual precipitation of only 470 mm in average. The trials were supported by the German Federal Ministry for Education and Research (BMBF), the German Perennial Nurseries Association (BdS), and the German Research Foundation (DFG). Till 2010 around 30 mixtures have been developed; fifteen have been optimized on the basis of knowledge and assessments gained in the project and are now published as recommendations (http://www.prof-kircher.de; FENZL & KIRCHER, 2009). Methods and results from the assessments are recorded by MESSER (2008), who elaborated many aspects of the research project in his PhD-Thesis, assumed by the University of Sheffield.
2.2. Perennial Mixtures from Further research institutions
Additionally to the research at Anhalt University a remarkable amount of mixtures with
promotional "trade names" were tested, assessed and optimized since the end of the 1990s
especially by these institutions:
Bayerische Landesanstalt fьr Weinbau und Gartenbau (LWG), Veitshцchheim (P.
SCHЦNFELD)
Schau- und Sichtungsgarten Hermannshof, Weinheim (C. SCHMIDT)
Lehr- und Versuchsanstalt fьr Gartenbau / Fachhochschule, Erfurt (C. PACALEI, W.
BORCHARDT)
Zьrcher Hochschule fьr Angewandte Wissenschaften Institut Umwelt und Natьrliche
Ressourcen, Wдdenswil, Switzerland (D. TAUSENDPFUND, A. HEINRICH)
Together with Anhalt University these protagonists currently are publishing 29
recommended
plant
mixtures
in
http://www.stauden.de/cms/staudenverwendung/mischpflanzungen/mischungen_alphabetis
ch.php?navid=87
The most widespread planting is "Silbersommer", a concept of 36 taxa, created by the
Arbeitskreis Pflanzenverwendung (Committee of Planting Design; see
http://www.stauden.de/cms/staudenverwendung/mischpflanzungen/forschung/ak_verwendu
ng.php?navid=93 )
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Randomly Mixed Combinations - Application Approaches for Planting Design.
2.3. Creating Applications of Randomly Mixed Perennial Plantings Small plots can be designed aesthetically satisfying with pure randomly mixtures. On bigger areas more predictability of the resulting planting is desired. Thus at Anhalt University some variants of mixed plantings were developed to enhance the quality of the designed vegetations appearance. Nevertheless they should not effect significantly more time consumption than working with the pure randomly mixing strategy. FENZL & KIRCHER (2009) published six application variants for practitioners. In chapter 3 these variants shall be introduced and explained by their theoretical background.
3. Results 3.1 Preconditions for Well Performing Mixed Plantings plant species have to be selected and arranged by taking into account the following trait (MESSER 2008): Choice of suitable site / habitat conforming (HANSEN & STAHL, 1993) Thematic focus of the planting (i.e. blue-yellow contrast) Growth rhythm (short-term dynamics, annual aspects, height in various seasons, long- term dynamics) Life expectancy of the plants (biennials, short- and long-lived perennials) Plant sociability (according to HANSEN & STAHL, 1993) Reproduction and rate of propagation Population biological strategies (runners, rhizomes) (GRIME, HODGSON & HUNT, 1986) Aesthetic criteria (layering, color combinations, texture) To guarantee a visually pleasing and sustainable relief within the planting, it is recommended to distinguish between 5 different plant categories according to height and long and short term space requirements (table 1)
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
The diversity of most mixtures is guided by around 12 to 20 species / cultivars per theme for sunny habitats. "Silbersommer" is the richest mixture with 36 taxa. Under shady conditions it is better to reduce the diversity appropriately. Concrete recommendations for mixtures in woodland habitats are currently investigated by tests of the Committee of Planting Design.
Category Definition
Recommende d proportion of plants
Dominant Forming the structural framework of the planting, e.g.
species: grasses (Miscanthus sinensis, Cortaderia selloana),
Structure Plants, large-leaved perennials (e.g. Rodgersia) or upright
frameWork Plants (e.g. Veronica longifolia); mainly C-, C-S or S-
plants
Strategists
5 ­ 15 %
Companion plants
Recurring, stabilizing elements (e.g. Salvia nemorosa, Hemerocallis lilioasphodelus) which define the visual character of the planting and emphasize the structure plants. Long lived plants; mainly C-, C-S or SStrategists
30 ­ 40 %
Ground cover plants
Usually small perennials of up to 30 cm height which must be used in larger numbers, usually as a carpet between gaps between plants of the first two categories, i.e. Geranium x cantabrigense, Omphalodes verna, Waldsteinia geoides; mainly C-, C-S or S- Strategists
50 %
Filler plants
Short lived plants, responsible for a quick cover and visual display in the first one to three years. Quick in growth and spreading generatively, but weak in competition, declining whilst substituted by the dominant, companion and ground cover plants (e.g. Linum perenne, Aquilegia canadensis, Digitalis purpurea); R-, R-S, or C-R-Strategists
5 ­ 10 %
Plants with a short growth period that do not require added much space. However, these are very showy and additionally in Scattered plants dominant when in bloom, such as flowering bulbs great amounts: (e.g. Allium sphaerocephalon, Anemone blanda, 20 to 50 bulbs / Narcissus `Hawera) or very slim perennials (e.g., mІ Codonopsis clematidea, Campanula persicifolia)
Tab. 1: Classification of perennials (MESSER 2008, definitions following BORCHARDT 1998, supplemented by FENZL & KIRCHER 2009; C-, R-, S- Strategy see GRIME, HODGSON & HUNT 1986
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Randomly Mixed Combinations - Application Approaches for Planting Design.
The diversity of most mixtures is guided by around 12 to 20 species / cultivars per theme for sunny habitats. "Silbersommer" is the richest mixture with 36 taxa. Under shady conditions it is better to reduce the diversity appropriately. Concrete recommendations for mixtures in woodland habitats are currently investigated by tests of the Committee of Planting Design.
3.2 Applications of Randomly Mixed Perennial Plantings The planning strategy of mixed perennial plantings can be recommended for small to medium sized beds in Public and Private green spaces, if a natural display is desired. Considering the proportions and amounts of plant- categories recommended in table 1 is essential for an attractive relief as mentioned above. Bigger scaled planting areas can be arranged in a meadowy style, allowing more intricate and intertwining plant structures: the proportions of taller species may be increased. Also combinations between sown vegetation and planted perennials are conceivable (see Fig. 8 / Variant 6). Suitable for tenders with mixed plantings are for example the following themes: Planted meadows, eventually in combination with sowing Planted prairies Mille-Fleur-plantings (seasonal bedding with small inflorescences, in well balanced color combinations) Woodland underplanting (mixes with lower diversity in species) Marginal plantings in ponds (reed forming plants shall be combined with only filler plants or rather shade tolerant ground coverers) Traffic islands and roundabouts as well as small plots between asphalt sealed surfaces Narrow beds along fences, walls and buildings Rock gardens and dry stone walls (plant lists divided into differentiated habitats like ,,sunny gaps", ,,shady gaps", "mural crown" etc.) Extensive roof gardens Plantings between pavement crevices
Particularly on bigger planting beds it might be beneficial not to dedicate the complete Plant Distribution to chance. Six adaptation possibilities are introduced hereafter:
Fig. 3: Variant 1 - Pure mixed planting list with names and quantities of plants (species, genus, variety, cultivars) Plants are arranged in similar distances to each other. The image on the right hand shows a randomly planted plot of "Bernburger Blьtenschleier"
plant list example: pattern on the plot 30 Aster amellus `Rudolf Goetheґ 25 Buphthalmum salicifolium 50 Carex montana 100 Thymus serpyllum `Albumґ etc.
planting plan example No depicted plan is necessary
distribution
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
Variant 2 - List with names and quantities of plants plus additional remarks about positioning or grouping The grouping of certain species allows to include areas providing a calming appeal. Groups in rows or streams are effective for grasses or vertically growing perennials like Campanula persicifolia or Verbascum spp. "Filler plants" do not leave an ugly hole after vanishing if arranged in narrow groups. It is also possible to prevent tall plants (dominant species) from being placed nearby the beds edge by only adding an appropriate written remark into the plant list. On vast areas the observers eye is assisted by a consistent use of all species in small groups, causing a "zooming" effect communicating with the extension of the complete planting beds size.
plant list example:
planting plan example
30 Aster amellus `Rudolf Goetheґ
No depicted plan is
in small groups of 3
necessary
25 Buphthalmum salicifolium
randomly distributed
50 Carex Montana
In linear streams of 5
100 Thymus serpyllum `Albumґ
in groups of 10
Fiegt.c4. :
Variant 3 - Illustration of tall, dominant plants in the plan,
accompanied by randomly mixed lower perennials
On middle and bigger sized areas it can be necessary to include taller
Plants into the vegetation pattern to provide visual leading. This can be
realized byadequate perennials, subshrubs or even shrubs arranged in
sufficient distances to each other. To create naturalistic distribution
patterns these species should be depicted into a graphical plan or
sketch. The shallower species can be added randomly as in variant 1 or
added by additional remarks about positioning or grouping as in variant 2.
distribution pattern on the plot
plant list example:
planting plan example pattern
3 Dictamnus albus 8 Stipa gigantea FVFiiaggir..ni66am::n32it05x4tABu­rusetpIe:lhrltuahsmatlremalltuuimosn`sRaoulfidccoilfelofalriGudomeefthineeґd recurring core groups 50 Carex montana 100 Thymus serpyllum `Albumґ etc.
distribution on the plot
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Randomly Mixed Combinations - Application Approaches for Planting Design.
Variant 4 ­ Illustration of clear defined recurring core groups accompanied by additional perennials in randomly mixture Core group planting = "Kerngruppenpflanzung" is defined by BORCHARDT (2006). To be sure that desired combinations of particular partners will be realized within the planting clearly specified groups can be depicted detailed (left alternative in box below). The same effect will result by using one symbol as placeholder for the specific species combination per core group. The rest of the designated perennials can be added randomly as in variant 1 or 2.The planting on the right hand shows repeated combinations of Gypsophila ,,Rosenschleier and Iris Barbata-Media , the former covering reliably the unpleasant summer appeal of the faded latter ones.
plant list example: pattern on the plot alternatively
planting plan example alternatively
distribution
7 Aster ,Pink Star,,
7 Core groups each with:
21 Allium aflatunense
1 Aster ,Pink Star,,
21 Hieracium pil. `Niveum
3 Allium aflatunense
21 Hieracium pil. `Niveum in mixture: 30 Aster amellus `Rudolf Goetheґ 25 Buphthalmum salicifolium 50 Carex montana etc.
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
Fig. 5: Variant 5 ­ subdividing the planting bed into smaller parts with Different mixtures or with the same mixture in different multitudes per species Extensive planting areas, for example several hundred square meters, may look too uniform if covered consistently with one mixture only. If partitioning into adequate sized plots it should be paid attention to form transitions from plot to plot or rather to refrain from colliding completely different plant combinations against each other. Neighbouring plots should contain similar ranges of species but arranged in different amounts respectively proportions. Of course this approach can be combined with all variants mentioned above inside of one single plot. The image shows a "Garigue" planting at the Botanical Garden of Wьrzburg: Different mixtures can be recognized, but some species such as Asphodeline lutea are skipping over the borders.
plant list example:
planting plan example
area A: 100 Aster amellus `Rudolf Goetheґ 50 Allium sphaerocephalon 60 Asphodeline lutea etc.
area B: 30 Aster amellus `Rudolf Goetheґ 300 Allium sphaerocephalon 24 Dictamnus albus etc.
area A area B
area C: 100 Allium sphaerocephalon
area C
Fig3. 08:Asphodeline lutea 8 Festuca gigantea
Fiegt.c6. :
Variant 6 - Combination of mixed plantings with seeding or
rather spontaneous vegetation
The most naturalistic approach is to combine existing vegetation or
seed mixes with a mixed perennial planting. To include pot plants or
young plants from trays is rewarding for vegetatively propagated
perennials (i.e. Hemerocallis cv.) as well as for species with a weak
or unreliable germination (Salvia species). Also plants with a very
slow development (Dictamnus albus) are worth to be planted as bigger
specimen.
plant list example: pattern on the plot
planting plan example
distribution pattern on the plot distribution
30 Iris `Libellulaґ 20 Salvia officinalis 15 Verbascum olympicum etc. plus sowing mixture (1g/mІ): 5 % Festuca pallens 2 % Dianthus carthusianorum 1 % Linum perenne etc. or scattered between existing spontaneous vegetation
No depicted plan is necessary
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Randomly Mixed Combinations - Application Approaches for Planting Design.
4. Conclusions & Outlook
4.1. Contemporary Strategies Related to Mixed Perennial Plantings Precursors of the mixed planting strategy were already performed in artificial prairie plantings such as the first prairie restoration project, the Curtis Prairie, in Madison, Wisconsin, USA. A combination of sowing, planting and transplanting sod (DIECKELMANN & SCHUSTER, 2002; WASOWSKI, 2002) was distributed in mixture. The "Matrix Planting" approach of Peter Thompson (THOMPSON 1997) is also based on mixed plantings. Oudolf combines a few mainly tall growing species in drifts or blocks which are neighboured to each other in borders, as can be seen at his famous "Wisley Border" in RHS Wisley Gardens (GERRITSEN & OUDOLF, 2000). The latter project can be characterized as an ornamental type of "variant 5" (Fig 7). Further examples of planting methods referring to the randomly mixed strategy see in MESSER (2008).
Fig. 7: Piet Oudolfs Border at RHS Wisley Gardens is a combination of diagonally running streams with mixed tall perennials 4.2. Mixed Plantings in Academic Education It is to be discussed which level of knowledge and skills shall be taught in academic landscape architecture courses based on four steps of intricacy: Step 1: Coming to know only the mixed strategy as one possibility beside monoplanting, planting in groups and habitat planting with sociability figures. To experience a synoptic view on existing mixtures from diverse research institutions and their implementation into the planning process. This step should be a fundamental target in undergraduate Landscape Architecture courses. Step 2: Understanding basically principles of functioning sustainable combinations such as habitat-conformance, well balanced strategy types and heights as well as a precise aesthetical concept. At least undergraduate students with emphasis in planting design should reach this level. Step 3: Ability to change existing mixtures in case of differing site conditions or aesthetical demands by substituting particular species according to their individual role within the planting. For this step it is important to mediate a deeper insight
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
into plant traits concerning ecological as well as aesthetical features. Postgraduate courses should target at least this step. Step 4: Ability to create individual mixtures. Profound plant knowledge is necessary as well as a grounded understanding of ecological traits and site demands of plants. Design skills and a well developed know how in aesthetical enhanced plant composition are to be educated intensively. This can be aimed in specific postgraduate courses focusing on planting design 4.3. Applications of Mixed Perennial Plantings in Academic Education Undergraduate courses should include at least variant 1 ­ 4 (see 3.2 Fig. 3-6) of mixed plantings to implement these methods into planning for public as well as for private gardens. Variant 5 (subdividing the planting bed into smaller parts with different mixtures or with the same mixture in different multitudes per species) demands more skills from the planner: to guarantee fluent transitions between neighbored plots mixtures have to be carefully changed in their species ranges (Step 3 in 2.2). Also a combination between mixed planting and sown or spontaneous vegetation (variant 6; Fig 8) requires this skills. So variants 5 and 6 can be targets for postgraduate courses for an adequate insight into site analyses, aesthetical and ecological principles are necessary as well as an adequate knowledge of plant ranges. Table 2 summarizes 7 levels combining the application variants from chapter 3.2 and the intricacy steps from the above chapter 2.2.
Optimizing the Visual Quality and Cost Effectiveness of Perennial Plantings by
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Randomly Mixed Combinations - Application Approaches for Planting Design.
Required knowledge
Variant Step
of Knowledg Knowledg Knowledg Knowledg
intricacy e
e
e
e
in Site
in
in
in
analysis aesthetic vegetation species
& design ecology
1
1
low
low
­
­
1
2
low middle low
low
2
1 ­ 2 middle middle low
low
3 / 4 1 ­ 2 middle middle low
low
1-4
3
high middle middle middle
Proposed for academic course Undergraduat e Undergraduate * Undergraduat e Undergraduat e Postgraduate
Time demand in plannin g very low low low middle high
5/6
3
high
high
high middle Postgraduate high
1-6
4
high
high
very
high
very
high
Postgraduate high
*
Tab. 2: Matrix for estimated required knowledge / skills, proposed level in academic Landscape Architecture
courses and predicted time demand in the planning process.
Knowledge levels: ­ = no knowledge required; low = basic knowledge; middle
= advanced knowledge;
high = professional knowledge
* for specific courses or studios focussing planting design
5 References Borchardt, W.(1998): Pflanzenkompositionen [Plant compositions]. Stuttgart: Verlag Eugen Ulmer Borchardt, W.(2006): Planungsstrategien fьr Staudenpflanzungen - Nachdenken lohnt sich. Deutscher Gartenbau 25 Dieckelmann, J., Schuster, R. (2002): Natural Landscaping - designing with native plant communities, 2nd ed, Madison, WI, USA: The University of Wisconsin Press Dunnett, N., Kircher, W., Kingsbury, N.(2004): Communicating ecological plantings. In Dunnett, N., Hitchmough, J. : The Dynamic Landscape. London and New York: Spon Press Fenzl, J. & Kircher, W. (2009): Bernburger Staudenmix ­ Ein Forschungsprojekt der Hochschule Anhalt. Bernburg, HS Anhalt (FH) Gerritsen, H. & Oudolf, P. (2000): Dream Plants for the Natural Garden. Frances Lincoln Grime, J.P., Hodgson, J.G. & Hunt, R. (1986): Comparative Plant Ecology, London: Unwin Hyman
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Wolfram Kircher, Uwe Messer, Jessica Fenzl, Marcel Heins & Nigel Dunnett
Hansen, R.; Stahl, F.,1993: Perennials and Their Garden Habitats. Cambridge University Press Kircher, W. und Trunk, R. (1995): Wenn der Zufall regiert - Naturnahe Bodendeckerverwendung. Deutscher Gartenbau 21 Kircher, W., 2000: Zufдllig gemischte Staudenpflanzungen [Randomly mixed perennial plantings]. Deutscher Gartenbau 32 Kircher, W, (2004): Planung von Staudenpflanzungen. Grьnforum LA 6 Messer, U. (2004): Stauden im Schatten der Bдume. Grьnforum LA 3 Messer, U. (2008): Studies on the development and assessment of perennial planting mixtures. Research Thesis for PhD, University of Sheffield, Department of Landscape, Sheffield, United Kingdom Robinson, N. (1998): The Planting Design Handbook. Aldershot, England: Goner Publishing Company Thompson, P. (1997): The Self-Sustaining Garden. London: Batsford Wasowski, S. (2002): Gardening with prairie plants. Minneapolis, MN, USA: University of Minnesota Press

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