Menu
In this chapter, we will learn about dendrology as a science and its relevance to park gardening. It is a scientific discipline that deals with the systematics (classification) and correct naming of trees and other groups of plants for study and introduction into everyday horticultural practice. In this chapter we will learn about the environmental factors that influence plant growth and development and the basics of Latin terminology.
Dendrology (Greek: dendron = tree and logia = science, Latin: arbor = tree) is the study of woody plants. The boundary between taxonomy and dendrology is not fully defined. The person who deals with dendrology is a dendrologist. Dendrology, as a science, studies trees in order to focus on the economic use of wood or trees and their identification and horticultural qualities (beauty or ornamental value).
Dendrology is defined as deciduous and coniferous trees or shrubs. Dendrochronology is the study of past events in the life of these plants.
Taxonomy (Greek táksis; nómos – law or lawfulness; Latin taxo) or (in biology) the older name systematics refers to the graded classification of things, or the principles that underpin classification. On the basis of what taxonomic system we can classify everything – organic objects, inorganic objects, places, events, and so on.
Taxonomies or taxonomic schemes are made up of taxonomic units (taxa) or types of things, often arranged in a hierarchical structure. They are usually related to each other by relations of inferiority and superiority, also called parent-child relations. In this type of relationship, the thing in the subordinate position has, by definition, the same constraints as the thing in the superordinate position, plus one or more other constraints.
Underneath are kingdom, phylum, class, order, family, genus, species. Between these classifications there are often several other levels (e.g. subclass, superclass, subfamily, subspecies, variety, etc.).
Originally, the term taxonomy referred to the classification of living organisms (known as alpha-taxonomy), but nowadays the term covers a much broader and more general area, referring to the classification of things and to the principles underlying such classification.
Scientific classification and biological systematics are very important subtypes of taxonomy in biology.
Vegetation is the most prominent natural-geographical element in the landscape. It depends on a variety of factors. These are called environmental factors. We distinguish:
The importance of flora:
Vegetation is a source of food used by humans and animals. Wood, cotton, flax, rubber are used as raw materials for industry. Plants undergo photosynthesis, which produces oxygen. In modern times, the natural environment and vegetation has become an important recreational space (running, walking, cycling …).
There are five groups of vegetation:
Plant biology is the study of plants, their origins, how they grow and how they are related. Dendrology is the study of woody plants. Dendrology – a collective term for trees and shrubs;
A tree represents the center of greenery with which to build an urban or private space. It has a pronounced shoot at the top of which the canopy branches out. The shape of the canopy can vary (round, oval, flat, columnar, weeping etc.);
A TREE has a trunk with a canopy and grows at the tip of the shoots and roots. It also has a secondary growth – an annual thickening of the trunk outwards. The shape of the crown and trunk varies greatly from tree to tree, giving them a distinctive look or habitus which is specific.
The habitus (the shape of the plant’s growth) can be regular or irregular. A regular habitus is round, ovate, conical, columnar. An irregular habitus is when the branches of the plant are of different lengths. All overhanging and umbrella-shaped canopies (Salix) have a very characteristic irregular habitus.
The tree is the center of greenery to which everything else is subordinated; it is strong and detracts from weaker plants; it works well in the background of weaker plants; it protects the space from noise, pollution, screens places we want to remain hidden;
The height of the trees is ranked as follows:
> 18 m high
Medium height 10 – 18 m
Low 5 – 10 m
Dwarf < 5 m
SHRUB – a woody, sessile system of shoots with branches growing out of the root neck; in a shrub, the main shoot is soon stunted and side branches develop.
SHRUBS play a central role between trees and herbaceous ornamentals, their variety of choice makes them versatile and popular, they can stand alone or be grouped together, they are flexible enough to be combined with herbaceous ornamentals, different combinations of evergreen, flowering, deciduous shrubs create varied images of green motifs that change throughout the year. They can be flowering or evergreen. The shrubs are divided into groups according to their growth:
SEMI-SHRUB is a transitional form between a shrub and a perennial. The lower part of the stem is woody, the upper part is herbaceous, which dies back, dries out or thaws at the end of the growing season (Rosa, Perovskia).
CLIMBING PLANTS (VINES) is a shrub whose branches and twigs climb up a support so that it leans, clings, climbs or twists. They are shrubs that need some sort of support.
We distinguish:
The size of the climbing frames:
The climbing plants are divided into three major groups according to their size:
Habitat – physical and biotic factors that are present in an area that allow a particular species to live
Habitus – knowledge of the growth forms of trees, shrubs, vines.
Roots – root plate (deep, medium, shallow); rhizomes (rhizomes or underground stems), root suckers. Roots are the lowest part and give the plant an anchor in the soil and supply water and minerals. They grow only at the ends (root hairs). Some conifers have shallow roots (Picea), others deep roots (Abies, Pinus).
Root collar – the joint or connection between the roots and the trunk. It is usually located above the soil. In some tree species it is clearly visible, in others less so.
Branches – may grow in an opposite, alternate, spiral or whorled pattern along the trunk. Branches may be erect, drooping, pendulous or horizontal. They form a canopy that bears the leaves and flowers.
Leaf – leaf durability where we distinguish: deciduous (usually leaves drop off in autumn), evergreen, winter-green (stay green on the tree until the following spring when new leaves appear). New evergreen leaves don’t fall off, but remain on the plant for several years. Conditionally evergreen leaves only fall off when it is really cold or during cold droughts. Textural density determines the shading of the canopy or the distribution of leaves. Autumn color may be very pronounced, pronounced, not pronounced, perceptible or lacking (leaves don’t change their color). Conifers have leaves transformed into needles to make them more durable in cooler living conditions.
Flower – flower designs are bisexual (hermaphrodite), heterosexual (male or female), monoecious and dioecious. Flower buds are formed in autumn (along the entire length of shoot, at shoot tip, on short shoots of dioecious or perennial wood, flowers sprout from perennial wood); flower and fruit develop in one growing season (on annual shoots); the timing and duration of flowering may vary due to differences between climatic zones, differences in topography and environmental conditions. These differences diminish towards summer, and towards autumn the plants flower at the same time throughout the country; flowering (dense, sparse, single) and flower or inflorescence size (small, very small, small, medium, large, very large); color of the flower.
Fruit – set of fruits or co-fruits (dense, sparse, singly), size and color of fruits, time when fruits are on the plant. The fruits of conifers are called cones. These are woody or fleshy and enlarged inflorescences of pollinated female flowers. They contain seeds, either woody or leathery, formed from seed cones, the lower part of which has leathery umbilical scales (bractia). These form the characteristics of each species. Most cones open at maturity and the seed falls out (Picea, Larix). Only some cones completely disintegrate, leaving only the axis of the cone on the shoot (Abies, Cedrus). Empty cones may soon fall off (Picea) or may remain on the tree for many years (Pinus). In some places, the seeds have wings so that they are more easily blown away by the wind. Some conifers do not have true cones, but berry-like formations (Taxus).
Physiological traits – tolerance or intolerance to different factors.
Use – function in the plantation, to be included individually or in groups in the space, design element, purpose, wildlife importance.
Growing conditions – soil conditions, climatic conditions (temperature, air and soil moisture).
The origin of the plant (provenance) – where it comes from or where it is native to.
Dormancy is a state of reduced metabolic activity that allows a plant to survive in unfavorable growing conditions. Dormancy occurs due to the effects of low temperatures and short days (depending on the length of time the sun is shining).
Photoperiodism – a shortened day causes most trees to go dormant. This means that non-native trees used in planting are leafed out later and lose their leaves a little earlier.
Thermoperiodism – lower night temperatures are crucial for those plants for which the shortened day does not affect dormancy preparations. Night temperatures below 10 °C, accelerate the transition to dormancy, especially for plants from latitudes south of the temperate zone (Aesculus, Fraxinus, Malus, Prunus avium, Syringa). On sites outside natural soils, the thermoperiodism is even more pronounced. On the positive side (proximity to concrete buildings and thus excessive warming) or on the negative side (shorter and earlier wood maturation in plants).
In this chapter, we will learn about the importance of Latin terminology in naming plants. We will define terms that illustrate particular characteristics of plants and learn about the general characteristics of woody plants (groups of ornamental plants, modes of branching, height of growth, etc.). We will learn about systematics, or the classification of plants into a single system, and learn how to use a plant key to identify plant species. This is the basis for identifying plants and using them in everyday practice.
The woody plants in our parks (trees, shrubs, climbers) are native or have been introduced from various areas. We are interested primarily in their ornamental value, their usefulness or utility and their cultivation techniques. We use them to manage the landscape, parks and gardens. They are thus an irreplaceable element in the integration of buildings and the environment. Their integration is a science that is not unique to one nation, but universal and therefore the plant names must be understood by all. Uniform naming was introduced as early as the 17th century by Carl Linné, a Swedish botanist. He wrote the names of plants in Latin and Greek, thus introducing the dual or binary nomenclature. Thus, each plant has two names – similar to a person; a surname and a given name. In gardening we also speak of varieties, which represent the smallest taxonomic unit. A variety usually illustrates a specific form of growth, mode of branching, variegation, etc.).
Latin is a dead language and is very precise in its expression. The grammar of Latin is clear and has its own peculiarities. Plant names are derived from Latin and Greek. That is why we simply call them botanical names.
International convention in horticulture is to capitalize the genus, lowercase the species, and capitalize the variety again in single quotation marks. It is common to find the botanical name of plants in texts written in italics: Fagus sylvatica ‘Pendula’.
Sometimes there is also a subspecies, variety, form or cultivar of a species. Sometimes we refer to the specialities by abbreviations, e.g. var. (varietas), cv. (cultivar), subsp. (subspecies), f. (form).
Example: Taxus baccata ‘Fastigiata’ – a cultivar of columnar yew; capitalize the variety in a single quotation mark. However, if the species is known in the wild, it is abbreviated var. (variety) or f. (form) and written with a lowercase italics and without quotation marks.
Plants have their own common names in every language, but these can also vary from region to region.
a) white:
ALBUS – white (Abies alba – white fir or hawthorn)
ALBIDUS – whitish (Cistus albidus)
ARGENTEUS – silver fir (Picea argentea)
CANDIDUS – snow white (Berberis candida)
VIRIDIS – green (Fragaria viridis)
CINEREUS – grey
b) yellow:
AUREUS – golden (Ribes aurea)
VITELLINUS – brownish yellow
c) red:
ATROPURPUREA/ATROPURPUREUS – variegated red (Acer palmatum ‘Atropurpureum’)
CARNEUS – flesh red, hardwood (Erica carnea)
PURPUREUS – red
ROSEUS – pink (Hibiscus, Rosa sinensis)
RUBRA – red (Acer rubra)
SANGUINEUS – red as blood, bloody (Ribes sanguineum)
d) black and other:
NIGRA – black (Pinus nigra)
SEMPERVIRENS – evergreen (Juniperus sempervirens)
SEMPERFLORENS – always flowering (Begonia semperflorens)
SEMPERAUREA – always golden
TRICOLOR – tricolor (Fagus sylvatica ‘Tricolor’)
VARIEGATUM – variegated (Thujopsis dolabrata ‘Variegata’)
VERRUCOSUS – warty
PENDULA – weeping (Betula pendula)
HORIZONTALIS – horizontal (Cotoneaster horizontalis)
FASTIGIATUS – upright, columnar (Fagus sylvatica ‘Fastigiata’)
ARBORESCENS – woody (Hydrangea arborescens)
PYRAMIDALIS – pyramidal (Cupressus sempervirens ‘Pyramidalis’)
PUBESCENS – downy (Quercus pubescens)
PUMILO – dwarf, low (Pinus pumilo)
REPENS – creeping, climbing (Taxus repens)
GLOBOSUS – round-shaped (Acer platanoides ‘Globosum’)
GLAUCA – blue-grey, bluish-grey (Picea glauca ‘Conica’)
NANA – low, slow-growing (Picea omorika ‘Nana’)
FLORIBUNDUS – Pieris floribunda
MULTIFLORUS – multiflora (Rosa multiflora)
POLYANTHUS – multi-flowered
GRANDIFLORUS – Magnolia grandiflora
FOLIUS – leaf
GRANDIFOLIUS – large-leaved (Fagus grandifolia)
FRAXINIFOLIA – ash-leaved (Pterocarya fraxinifolia)
CARPINIFOLIA – hornbeam-leaved (Ostrya carpinifolia)
PARVIFOLIUS – small-leaved (Rubus parvifolius)
MACROPHOLIUS – Magnolia macrophylla
MACROCARPUS – Cupressus macrocarpa
CONIFER – conifererous
RACEMOSUS – clustered fruit (Sambucus racemosa)
CAMPESTRE – Field (Acer campestre)
VULGARE – ordinary (Syringa vulgaris)
ATLANTICA – Atlantic (Cedrus atlantica)
ALPINUS – Alpine (Ribes alpinum)
MONTANA/MONTANUS – Mountain (Ulmus montana)
PALUSTRIS – marsh (Caltha palustris)
OFFICINALIS – healing (Rosmarinus officinalis)
CHINENSIS – Chinese (Juniperus chinensis)
PERSICA – Persian (Parrotia persica)
OCCIDENTALIS – Western (Platanus occidentalis)
ORIENTALIS/ORIENTALE – Oriental (Platanus orientalis)
HORTENSIS – garden (Satureja hortensis)
SYLVATICA – forest (Fagus sylvatica)
ODORATA – fragrant (Rosa odorata)
MAYOR – large (Vinca mayor)
MEDIA – medium (Taxus x media)
MINOR – small (Vinca minor)
In this chapter, we learned the basics of Latin terminology and the names of ornamental plants. We learned how ornamental plants grow and the basic parts of a plant and their importance in the structure of a plant. We defined the importance of binary nomenclature in everyday gardening work.
In this chapter, we will learn about the environmental factors that influence plant growth and development and the cultivation requirements of ornamental plants. We will learn about the propagation methods of conifers and deciduous plants. We will look at the classification system of conifers and deciduous plants and see the relationships between them.
The environmental factors that affect plant growth and development are:
WATER: there are drought-loving plants or xerophytes that can adapt to dry growing conditions (cacti), and moisture-loving plants or hygrophytes that need right or medium moisture (Salix – willow, Populus – poplar), mesophytes.
LIGHT: has an important effect on plant growth and photosynthesis. It is the main generator of plant development. Plants that love a lot of light are called heliophytes.
TEMPERATURE: we distinguish between warm-loving (Juglans, Prunus, Gymnocladus dioicus, Magnolia) and cold-loving (Picea, Larix, Abies) plants;
SOIL: the plant draws nutrients from the soil, which also supports it;
TERRAIN: As climate changes with altitude, so does vegetation, creating altitudinal vegetation climate zones;
SOIL THICKNESS: Thinner soil on slopes;
HUMAN: alteration of natural vegetation (shrinking and reshaping by humans);
Figures 7 and 8: Gymnocladus dioicus – Kentucky coffee tree. Source: Ribič, P. (2023)
It is a very important piece of information when using trees for planting. Appropriate plant selection allows for economical maintenance compared to planting that neglects this aspect. It is therefore necessary to know the growth factors and ornamental value of each plant.
There are differences in terms of cultivation complexity:
Undemanding species – suitable for public plantings. These are species and varieties that grow well on most sites. They require little work and resources to maintain, provided they are planted in such a way that ecological and economic considerations are taken into account in addition to design considerations.
A low-demanding, adaptable species – suitable for planting in gardens, but only as companion species and varieties in public plantings. They are more labor and resource intensive to maintain and bring more color, habitats, structures and textures to the space.
Species and varieties for hobbyists – these are demanding species and varieties in terms of habitat. They are only planted in public plantings in exceptional circumstances (e.g. around monuments). They are difficult and expensive to maintain.
Species and varieties for collectors – these include rare species and varieties and novelties that are too expensive for public plantings. Special maintenance requirements such as protection from cold, rainfall are taken into account. They need a lot of work and resources to grow well.
Some of the terms used in park gardening
Endemic – a plant that grows only in a limited area.
Native tree species – indigenous, native, original tree species.
Naturalized – a fully adapted plant species that is basically native to our climate zone from other places.
Alpinetum – a plantation of alpine plants, mainly for study or ornamental purposes.
National Park – a large, natural, circumscribed, predominantly pristine area with ecosystems and natural attractions of major or exceptional importance for the Republic of Slovenia, intended primarily for the conservation and study of natural ecosystems and for recreation.
Landscape park – an area of cultivated nature that combines different landscapes with natural and cultural heritage components.
Monument of designed nature – a small area of garden or park design with botanical, aesthetic or cultural significance.
Horticulture – an activity that is concerned with the improvement of living space for cultural reasons.
Basophil – basophilic plant – a plant that thrives on alkaline soil; soil on carbonate alkaline soil.
Binary nomenclature – the dual naming of plants and animals in order to unify and make comprehensible names for all living things in the world.
Phenology – the science that deals with the phenomena of periodicity in the living world (leafing, flowering)
Monoculture – a plantation of a single tree (or other) species.
Figures 10 and 11: The right plant in the right place. Completely unsuitable site for tree of heaven (Ailanthus altissima) on the left and not enough room for root growth in maple on the right. Source: Ribič, P. (2021).
All plants in the system are classified into phyla, classes, orders, families, genera, species, subspecies.
The whole plant system is divided into two groups:
The important plants for gardeners are the seed plants or spermatophytes, which can be either gymnosperms or angiosperms. Gymnosperms are the oldest plants. They include specimens that are over 4000 years old. Most woody plant species are found among the angiosperms, especially the dicotyledons. Woody plants among the monocotyledons are found only in the palm family (fam. Palmae) and in the lily family (fam. Liliaceae), genus Ruscus.
There are between 300.000 to 400.000 estimated species of seed plants, which are the most highly evolved plant group. They have flowers, fruits and seeds, the embryo of which is the result of the union of the female and male gametes (sexual reproduction).
Seed plants are divided into:
Figures 12 and 13: Coastal redwood (Sequoia sempervirens). Source: Ribič, P., 2023
Conifers are identified by their needles (transformed leaves), which have the same role as leaves in deciduous trees. Leaves can be thin, thick, leathery, stiff needles or scales. They can be light green, blue green, dark green, black green, white variegated, yellow or golden yellow, brown, orange or copper in color.
They are found from sea level (pines) to the tree line high up in the mountains (larch, dwarf pine). The leaves are mainly evergreen, but some shed their needles in winter (e.g. larch, swamp cypress, dawn redwood).
Conifer flowers are always heterosexual and monoecious or dioecious. Conifers usually bear flowers only on the upper branches of older plants. When the pollen matures, the anthers open and the wind carries pollen far away.
The fruits of conifers are usually called cones: these are the woody or fleshy and enlarged inflorescences of pollinated female flowers. They contain seeds, either woody or leathery, formed from seed cones bearing leathery umbel scales. These constitute the characteristics of each species. Most of the cones open at maturity (Picea) and the seed can fall out. Only a few cones completely disintegrate, leaving only the axis of the cone on the shoot (Abies, Cedrus). Empty cones can remain on the tree for many years (in many Pinus species).
Some conifers do not have true cones, but berry-like cones, such as juniper berries, where the fruiting scales are fleshy – the cone always develops from the inflorescence.
In some conifers (Taxus, Torreya), the fruit cannot be a cone because it has developed from a single flower. Here the seed is surrounded by a fleshy sheath.
Conifers reproduce in three ways:
We are talking about seed or generative reproduction and non-seed or vegetative reproduction. Seedlings grow faster than vegetatively propagated plants. Propagation by seed is only possible in natural species.
Cuttings are used to propagate rare species from which no seeds are obtained or when seed germination is unsuccessful. Propagation by cuttings is an option if the seedlings do not retain the characteristics of the species and are too genetically diverse.
Grafting is common in the propagation of varieties that have characteristics of slow growth, needle color and so on. Certain ornamental plants can only be propagated by grafting (Cedrus atlantica ‘Glauca Pendula’, etc.).
Angiosperms are divided into:
Monocotyledons are plants with a single cotyledon, mostly herbaceous, with tufted roots, sessile leaves and three-petalled flowers.
Dicotyledons are plants with two cotyledons, a cambium in the stem, so they can be woody, leaves are usually petiolate, variously shaped, and flowers are two-, four- or five-petalled.
We distinguish between herbaceous and woody plants in terms of their use. Deciduous trees may drop their leaves in autumn, so we are talking about deciduous plants that dominate the environment. There are also evergreens, of which there are very few.
Depending on their use, broadleaved deciduous plants can be divided into the following groups:
Characteristics of deciduous trees
Propagation of deciduous trees
In this chapter, we learned why it is important to have double names and what the Latin terms in plant names mean. We have identified the importance of woody plants in landscape use and learned about the systematics of ornamental plants in the plant system. We learned to distinguish between conifers and deciduous plants and to identify and describe the importance of the main plant parts (root, stem, crown, leaf, flower and fruit). We learned the most common methods of reproduction in ornamental plants. We learned about the differences between naked and covered seeds and how to find the main characteristics of each group.
In this chapter we will learn about the importance of ornamental plants in everyday gardening and their diversity. We will distinguish plants from each other and classify them according to their intended use (solitaire, ground cover, avenues, graves and cemeteries). We will learn about the importance of the ornamental value of plants.
In the early periods, the emphasis was mainly on utility. Trees were valued above all for their fruits and, indispensably, for the shade created by their large canopies. In the 18th century, trees took on a completely different role in the outdoor space. Trees planted as solitaire (individually) or in groups became a more prominent design element.
The tree plantation has become valued for:
Today, trees are the most indispensable and distinctive element in a landscape:
Tree communities (phytocenosis): a plant community is a grouping of plants with similar ecological characteristics and requirements, grouped together by climate, soil, area, etc.
In our environment, we learn about the most favorable sites where the trees are of the same or similar origin, e.g.:
Knowing how tree respond to soil and aboveground factors is crucial for the use of plants in a space:
Ornamental plants are brought from different environments for their ornamental value. As we have learnt through the plant system, we have different trees/shrubs/plants… and different ornamental values for different purposes. Ornamental value includes: variegation, branching, columnar, pendulous, drooping growth, size, shape and color of leaves, flowers and fruits, texture of bark, etc.
Depending on their ornamental value, plants are combined in different plantings according to the purpose and needs that arise (garden, public space, park, factory, cemetery, roundabout, yard, terrace, pergola, roofs and walls, etc.). Due to the costs associated with the planting layout, appearance and needs of the space, we always choose suitable plants according to the height and width of the growth, the leaf fall and other characteristics that each plant has. Ornamental planting should always be combined in group plantings, as multiple planting provides good screening and thus helps against unwanted views.
In this subsection we will learn what non-native trees are and their importance in horticultural planting. We will learn about the importance of temperature zones and acclimatization stages for ornamental trees. We will learn about the causes of winter plant decline.
As trees often come from warmer places, they usually need some time to adapt or acclimatize. As temperatures start to drop at the end of summer, the trees begin their first preparations for dormancy. This is when the winter buds begin to form, which are fully developed when the leaves turn brown and fall off.
Hibernation
In hibernation, the protoplasm, cell and tissue are ready to withstand the cold: – 15°C, – 20°C and more. The temperature range that a plant can withstand without damage varies from species to species.
Our climate is characterized by daily highs of over 10°C often as early as the end of January, followed by winter lows in January. Therefore, plants from such areas, where this is a common occurrence, do not usually respond to a short period of warmer temperatures.
However, plants that do not hibernate, i.e. plants from lower latitudes, respond quickly, for example Magnolia, Paeonia suffruticosa, Rosa sp..
Many trees need to experience a lower temperature for a certain period of time to go from true dormancy to dormancy and awakening, such as Acer, Forsythia, Chaenomeles, Pinus, Prunus etc.
Choosing tree species for winter hardiness
Overwintering hardiness zones allow a simple and quick assessment of the suitability and likelihood of survival of a stand.
Worldwide, winter hardiness zones are being successfully used on trees introduced from elsewhere. Less so in Europe because the weather is much more variable and unpredictable due to the Alps and the proximity of the Atlantic Ocean.
Winter-proof zones
Maps of the winter hardiness zones of woody and perennial plants have been produced for the European area. The maps show the areas in which each tree species can be expected to withstand low temperatures. This information is an additional aid to the plant selection.
Well-aged wood in the case of trees is much stronger than un-aged wood in the case of low temperatures. Plants from colder zones do not freeze in warmer zones, but this does not mean that they will grow well.
Table 2: Table from Heinze and Schreiber, 1984
| PAS | Minimum average winter temperatures in degrees | Areas in the band | Indicator species reaching the extreme limits of their cultural range in the belt |
|---|---|---|---|
|
5a |
-28,9 to -26,1 |
Belarus, Baltic countries. |
Acer campestre Cornus mas |
|
5b |
-26,0 to -23,4 |
north-eastern Poland, northern Ukraine, southern Finland, central Sweden, valleys in the central Alps, and high plateaus: the Bloch Plateau. |
Acer campestre Cornus mas Taxus sp. |
|
6a |
-23,3 to -20,6 |
Eastern Poland, south-eastern Sweden. |
Buxus sempervirens Hedera helix Quercus petraea |
|
6b |
-20,5 to -17,8 |
Central Poland, eastern Hungary, Czech Republic, southern Sweden. |
Buxus sempervirens Hedera helix, Quercus petraea |
|
7a |
-17,7 to -15,0 |
eastern Germany, western Poland |
Cedrus atlantica Ilex aquifolium Prunus laurocerasus |
|
7b |
-14,9 to -12,3 |
Central Germany, southern coast of Sweden, eastern. The Netherlands, eastern Denmark |
Cedrus atlantica Ilex aquifolium Prunus laurocerasus |
|
8a |
-12,2 to -9,5 |
central Netherlands and Belgium, northern and central France, northern England. |
Araucaria araucana Cupressus sempervirens Magnolia grandiflora Pinus pinaster Quercus ilex |
|
8b |
-9,4 to -6,7 |
The Dutch coast, western France, central England, northern Italy.. |
Araucaria araucana Cupressus sempervirens Magnolia grandiflora Pinus pinaster Quercus ilex |
|
9 |
-6,6 to -1,2 |
southern France, central Italy, central Spain. |
Chamaerops humilis Laurus nobilis Olea europaea Pinus pinea Viburnum tinus |
The purpose of knowing the winter hardiness zones is to reduce the likelihood of making the wrong choice of plants in plantings. It is particularly relevant for plants from warmer areas.
General observations on woody plants:
How can we prevent or reduce frost damage to plants?
Physiological drought of evergreen plants
Physiological drought is a phenomenon that often occurs towards the end of winter, when the sun intensity becomes stronger. The conditions for the onset of physiological drought are low temperatures, frozen ground and low humidity. On sunny days, evaporation is further increased by the solar heating of the leaves. Drought is particularly pronounced in vertical greening, green roofs, containers and troughs where the growing layer is thin.
Many trees from humid climates, which usually have larger evergreen leaves, cannot replace the moisture lost from frozen ground, so drought can cause damage to them.
Plants with needles such as Pinus mugo, Pinus cembra, Picea abies, Picea pungens are better adapted because they come from areas where cold drought is of normal occurrence.
Plant response to physiological drought
The damage is expressed in discoloration of leaves. The annual wood increment can also be damaged by low temperatures. Plant parts and tissues desiccate due to physiological drought. Protecting plants from physiological drought should include choosing sun and wind sheltered sites. Protecting the most sensitive plants with trunk protection (shades), spraying with anti-transpirants and keeping the site moist even in winter works well.
Levels of plant sensitivity to physiological drought
Very sensitive; surviving only in places with mild and wet winters. Viburnum davidii, Ficus carica, Photinia, Perovskia etc., survive in inland only with adequate winter protection in sheltered positions.
Sensitive: need a lot of humidity. They tolerate colder temperatures with snow cover. They often freeze due to late frosts and suffer from drought in dry winters when the ground is frozen. These are species that grow in shade, near to a water source and at higher altitudes where the temperature inversion makes it less cold and dry: Daphne sp., Hedera helix, Ilex aquifolium, Pieris japonica, Lavandula sp. etc. They are planted in positions sheltered from the wind. The most sensitive genus is Ruscus hypoglossum, which needs light shade all day. Most of these plants can be found in places with a continental climate.
Not very sensitive; widespread plants in Central Europe, non-native plants naturalised or at the stage of cultural acclimatisation: Cytisus scoparius, Mahonia aquifolium, resistant varieties of Prunus laurocerasus, Viburnum sp. and many conifers: Chamaecyparis sp., Juniperus sp., Thuja sp.
Plants only suffer physiological drought or cold damage in extreme years.
Insensitive; can tolerate large temperature differences, including low winter temperatures and dry air. Snow cover is poorly tolerated, with the exception of Pinus mugo. These plants grow well in a busy urban environment. Of the evergreens, these are mostly conifers with needle-like leaves from similar natural habitats.
The completely insensitive; grow on sun and wind exposed sites, i.e. Juniperus communis, Juniperus sabina and many others.
In this chapter, we learned about the term non-native trees and how they are acclimatized in space. We learnt about the causes of winter plant decline.
In this chapter we will learn about the importance of maintenance and pruning of woody plants. We will go through the different plant groups and identify the interventions needed to keep the trees well-grown and healthy in their mature years.
Conifers are not pruned as intensely as deciduous trees, as they have a much lower regeneration capacity, with the exception of some genera such as yew (Taxus) and Thuja. Usually, no more than one-third of the entire canopy is removed. Always leave the part of the branch that is alive and has needles, as this is where replacement shoots develop.
Removing the green parts slows down growth and weakens the plant. Cut the longer and more prominent branches just above where they join the shorter branch. The top is normally not cut. Prune them little by little, continuously, each year.
Pine is cut using the pinching technique. In spring, when the shoot starts to grow, the needles are still undeveloped. 2/3 of the shoot can be pinched off with the fingers to keep it growing. By pinching, the growth of the lateral buds (shoots) is encouraged, thus increasing branching.
Figures 22 and 23: Yew (Taxus) hedge, considered to be the best example of old wood pruning. Source: Ribič, P. (2021)
Pruning shrubs
To prune shrubs correctly, we need to have a thorough knowledge of their ornamental characteristics such as growth form, flowering time and flowering method. They are plants with a relatively short life span, even shorter when their ornamental function is at its peak. It is therefore generally not advisable to prune old and weak plants.
The shrubs grown for ornamental shoots should be pruned quite intensely. All forms of shrubs, however, need to be pruned regularly to remove dead and diseased shoots and to make room for new shoots. Pruning generally encourages growth. For example, if you cut back a one-year-old shoot, several new shoots could sprout in the pruned area. This is beneficial if we are restoring an older shrub or managing a young shrub. However, if we prune back a mature flowering shrub too much, it will start to grow faster and as a result there will be less flowering.
Some shrubs need almost no pruning, as they only develop a nice shape over the years. E.g. Viburnum, Rhododendron, Hamamelis, Magnolia. For such shrubs, we mainly remove only damaged, diseased and dry branches. The diseased branches are also cut back to a part of the healthy wood to encourage the growth of new shoots.
Depending on the time of pruning, shrubs are divided into two groups:
Shrubs that flower before mid-June; spring flowering, flowers on last year’s shoots. They are pruned immediately after flowering. Such shrubs include forsythia, Japanese quince, Japanese kerria, Weigela, etc.
Shrubs in the second group, such as summer- and autumn-flowering medlar, five-leaved, deciduous cherry and others, flower later, from mid-June onwards, and bloom on annual shoots. They are pruned in late winter or early spring.
Climbers are shrubs whose branches and twigs are not self-supporting, climbing up the support by leaning, clinging or wrapping around the support. In size, they can be over 10 m high, medium height from 4 – 10 m or low height less than 4 m.
Before the climber starts to sprout, select 3-4 shoots to form the growing frame. The remaining parts are cut back severely. The selected shoots are attached to the support so that the direction of their development is already indicated. In the following years, we will continue to encourage the growth of the selected shoots, while the others will be cut back vigorously. Once established, climbers generally do not need any special pruning, with the exception of particularly vigorous species, where it is necessary to hold back growth (pruning twice a year) and to cut them back occasionally to free up space. If left unmanaged, for example, Wisteria, Bignonia … lose their ornamental appeal and turn into a tangle of leaves and branches, giving them a neglected appearance.
Other climbers develop moderately and do not need special pruning, but respond positively to some other cultivation work, such as mulching. The mulch protects the plants from the winter cold and maintains soil moisture in summer. This is done using extremely small and less vigorous shrubs planted close to the climbers, or a mulch material consisting of leaves or bark.
Some specific interventions needed for proper maintenance of climbers:
Wisteria sinensis: if you want to restrict the development to a specific area, take action after flowering, i.e. in the summer on this year’s branches, by shortening them to 20-30 cm, then shortening them again in winter to 3-4 buds from which new flowers will develop.
Lonicera caprifolium: produces a very large number of fragrant flowers from April to late summer. As it ages, the honeysuckle likes to develop a dense tangle of branches at the top, but it is bare at the ground and forms strong rosettes. To keep the plant from being overgrown from the ground to the top, the canopy is pruned each year, thinned by 50% and the new growth cut back. Cut back the shoots 15-30 cm above the ground. Damaged branches and shoots are pruned.
Clematis sp.: Clematis are divided into two groups: botanical or small-flowered, which flower in spring or early summer (C. alpina, C. montana), and hybrids with larger flowers, which flower from June to the end of September. The former are bold and rustic and do not need pruning unless they have to be kept back due to space constraints. For spring-flowering Clematis, prune after flowering. If they are to be retained, the oldest, dry and weak branches are removed at the base to encourage new shoots to form. Repeat this process every two or three years. The flower shoots for the next growing season are formed on mature stems, shortening each damaged shoot to a healthy pair of buds or to the main stem.
Campsis radicans: Fast-growing climber with luxuriant growth. It climbs with roots sprouting from the trunk. Initially needs a low pruning to select and direct the main branches. However, when the plant reaches the desired size, prune in spring, when excessive development is discouraged, leaving 5-6 buds on the side branches to develop the shoots that will bear the flowers (annual shoots). We try to rejuvenate old specimens by pruning the plant cleanly to the ground in winter, removing the weakest shoots in the following season, and keeping only two or three strong branches, which are tied to a support.
Removing inflorescences that have flowered (four weeks after flowering) – great care should be taken since young shoots are very fragile and break off quickly.
The rejuvenation pruning is carried out in April and the shrub will be green again by the next growing season.
Watering – compulsory before the onset of winter, in winter when the ground is not frozen, and also in March when there are periods of no rainfall. Leaves should not be allowed to wilt and dry out during the growing season. Water with rainwater.
Fertilization – the bigger the leaves, the greater the need for fertilization. Fertilize from April onwards with a rhododendron-specific fertilizer, which is dug into the soil, taking care not to damage the shallow roots. Nitrogen deficiency causes yellowing of the leaves, chlorosis is common due to iron deficiency in soil that is not acidic enough – nutrient deficiencies lead to increased disease and pest infestation.
Root care – shallow-rooted cuttings are very poorly tolerated and hoeing becomes unnecessary.
Maintenance pruning – regular pruning is the most important task for all shaped hedges. The more often a hedge is pruned, the more beautiful and uniform its appearance.
Pruning a natural looking hedge
Timing of pruning of natural looking hedges: spring flowering shrubs such as forsythia, lime and Japanese quince are pruned after flowering. Species that can withstand rejuvenation can be pruned in winter if necessary by removing large parts of the plants. Conifers are pruned when they reach the desired height, summer and autumn flowering plants are pruned prior to flowering, in the spring.
Pruning and trimming of free-growing or unpruned hedges is done as much as necessary:
Pruning a clipped hedge
The size and shape, development and growth of the clipped hedge is controlled by regular shearing and rejuvenation pruning. The shape and size of the hedge is already being established by shaping pruning at seedling establishment. The shaping of individual plants moves on to the shaping of groups of plants, where we are no longer dealing with a single plant, but with a group of plants that form the hedge as a whole.
As the hedge grows larger each year (despite regular trimming) and changes shape, we occasionally need to rejuvenate it. This is of course taking into account that most conifers cannot tolerate more extensive rejuvenation and that other plants react differently to intensive pruning.
Pruning time for clipped hedges
Each hedge needs at least one pruning a year, so we use plants that can tolerate pruning well. The best time to do this is at the end of June. Deciduous trees will have mostly finished their initial shoot growth, and the second shoot growth would have started. An important reason for this timing is bird protection. In early summer, the hatchlings are ready to fly and leave their nests.
For the majority of vigorously growing plant species, shearing is recommended 2 times a year. The first time is in late February or early March, on frost-free days (e.g. Carpinus). The second time is when the initial growth has slowed down a bit, i.e. in late June. Strongly growing hedges such as Hornbeam are strongly recommended for summer pruning.
The final time to cut the hedge is when the growth is over and the wood is still maturing in August. Later pruning is not recommended because the fresh shoots need to strengthen (slow down) by autumn. If pruned too late, the new branches will not become woody (mature) before winter. We cut weak growth only in spring, evergreen hedges are pruned a second time in August after the June pruning.
Cut hedge design rule
The hedge needs a shaping cut. As a rule of thumb, the hedge should be 10 cm narrower for every meter of height, so that the lower branches get enough sunlight. Such a hedge is also better able to withstand thick snow cover and wind.
The top shoots of certain plants should not be cut back until they reach their intended height. Otherwise the top of the hedge will be unsteady and unbranched, but will thicken with subsequent pruning. It should therefore be pruned regularly at the sides to shape and thicken it.
Most of the hedges we grow here in Central / South Europe are shaped into a flat top. Although, for design and cultivation reasons, the upper surface may also be arched.
We learned about the importance of caring for and maintaining ornamental plants. The fact is that cultivated ornamental plants need to be cared for to keep them vital and healthy in old age. In this way, they could have a significant impact on the appearance of the public landscape and will not pose a danger to residents. It is therefore most important to know the plants well, to distinguish them and to take appropriate care of them.
Test your knowledge in the following quiz and see if you understood the contents of this section:
ArborTech project has been funded with the support from the European Commission, with the reference number 2021-1-SI01-KA220-VET-000028108. The content of this website reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.