Science and the Garden The Scientific Basis of Horticultural Practice third edition

Edited by David S. Ingram, Daphne Vince-Prue and Peter J. Gregory

Science and the Garden About The Royal Horticultural Society

The Royal Horticultural Society is the UK’s leading gardening charity dedicated to advancing horticulture and pro- moting good gardening. Its charitable work includes providing expert advice and information, training the next generation of gardeners, creating hands-on opportunities for children to grow plants and conducting research into plants, pests and environmental issues affecting gardeners. Science and the Garden The scientific basis of horticultural practice

E D I T E D B Y David S. Ingram Daphne Vince-Prue Peter J. Gregory

THIRD EDITION This edition first published 2016 © 2016 by John Wiley & Sons, Ltd. Published in association with the Royal Horticultural Society. First published 2002 by Blackwell Science Ltd; Second Edition 2008 by Blackwell Publishing Ltd.

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Library of Congress Cataloging-in-Publication Data Science and the garden : the scientific basis of horticultural practice / edited by David S. Ingram, Daphne Vince-Prue, Peter J. Gregory. – Third edition. pages cm Includes bibliographical references and index. ISBN 978-1-118-77843-2 (pbk.) 1. Horticulture. 2. Gardening. I. Ingram, David S. II. Vince-Prue, Daphne. III. Gregory, P. J. SB318.S29 2016 635—dc23 2015024749 A catalogue record for this book is available from the British Library. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Cover images: Large image [of garden steps and gate; Fig. 1.1 in 3rd edition] - Photograph © David S. Ingram. Top small image [flower with hoverflies; Fig. 18.3c in 3rd edition] - Photograph © and reproduced courtesy of the University of Warwick. Centre small image [rooted cutting; Fig. 11.5c in 3rd edition] - Photograph © and courtesy of the Royal Horticultural Society. Bottom small image [half flower of Antirrhinum; Fig. 3.5 in 3rd edition] - Scan and © John Bebbington, FRPS. Set in 8.5/12pt Meridien by Aptara Inc., New Delhi, India

1 2016 Contents

Preface to third edition, xiii Connecting with the stem, 25 Preface to second edition, xiv Leaf fall, 25 Preface to first edition, xv Leaf patterns: phyllotaxy, 26 Variations on a theme, 26 1 Diversity in the plant world, 1 The stem: reach for the sky, 27 Summary, 1 The growing point, 27 Introduction, 1 Forming new leaves, 28 Creating order out of disorder, 1 A tower of strength, 28 Colonisation of the land, 4 Secondary thickening: the formation of wood and Communities and the diversity of life forms, 6 bark, 29 Conclusion, 12 Bark, 30 Further reading, 13 Stem modifications, 31 Authors and affiliations, 13 The root: mining for minerals and water, 32 The structure and growth of the root, 32 2 The plant body: structure and function, 14 Storage roots and other modifications, 33 Summary 14 Nitrogen fixation, 34 Introduction, 14 Mycorrhizas, 34 Energy flow in the biosphere: photosynthesis and Conclusion, 35 respiration, 14 Further reading, 36 The light reaction of photosynthesis, 14 Authors and affiliations, 36 The dark reaction of photosynthesis, 14 C-3, C-4 and CAM plants, 14 3 Reproduction: Securing the future, 37 Respiration, 16 Summary, 37 Photorespiration, 16 Introduction, 37 Global significance of photosynthesis, 16 Vegetative reproduction, 37 The leaf: into the labyrinth, 17 Sexual reproduction, 38 The manufacturing centre, 17 Cones and flowers, 38 Cells, 17 Alternation of generations, 41 Water relations of cells, 17 Floral diagrams and formulae, 41 Layout of the leaf, 17 Seeds and fruits, 42 Controlling gas and water exchange, 17 Other fruits, 42 Protection against harmful radiation, 19 Conclusion, 44 Palisade tissues: the sites of photosynthesis, 21 Further reading, 44 The transport system, 21 Authors and affiliations, 44 Movement of water, minerals and hormones in the xylem, 21 4 Naming plants, 45 Transport of carbohydrates and hormones in the Summary, 45 phloem, 22 Introduction, 45 Producing new xylem and phloem: the cambium, 24 Latin botanical names, 45 The bundle sheath, 24

v vi Contents

Taxonomy: order in diversity, 47 Conclusion, 74 New developments, 47 Further reading, 74 Cultivated plant taxonomy, 48 Authors and affiliations, 74 Distinctiveness, 49 Uniformity, 49 6 Summary, 75 Stability, 49 Introduction, 75 Why plants change their names, 49 Why do plants need soil?, 75 Taxonomic changes, 49 What do plants want from the soil?, 75 Nomenclatural changes, 50 How soils are formed, 75 Misidentification, 50 Physical properties of soils, 76 The quest for stability and linking information Chemical properties of soils, 79 systems, 50 Biological properties of soils, 80 Botanical plant name stability, 51 Roots and soils, 82 Cultivated plant name stability, 51 Conclusion, 85 How to identify a plant, 52 Further reading, 85 Conclusion, 53 Authors and affiliations, 85 Further reading, 53 7 Soil cultivation and fertility, 86 Authors and affiliations, 54 Summary, 86

5 Selecting and breeding plants, 55 Cultivating the soil, 86 Summary, 55 Managing soil nutrients, 88 Introduction: adaptation and design, 55 Sources of the major plant nutrients, 89 Genes, 56 Fertilisers, 91 Gene regulation, 58 Manures, 93 Chromosomes, 59 Composts, 93 DNA replication, 60 Managing soil pH, 94 Genomes, 61 Managing water, 96 Gamete formation, 61 Soil-less growing media, 98 Recombination, 62 Conclusion, 101 Allelic variation, 62 Further reading, 101 Mutation, 62 Authors and affiliations, 101 Transposons, 62 8 The plant environment: Light and water, 102 Somatic and germ line mutations, 64 Summary, 102 Chimeras, 64 Introduction, 102 Heterozygosity and homozygosity, 67 Light and photosynthesis, 102 Dominant and recessive alleles, 67 The measurement of light, 103 Breeding systems, 68 Controlling gas exchange, 104 Breeding inbred lines, 69 Effect of the environment on photosynthesis, 105 Breeding open-pollinated populations, 69 The effects of shade, 105 Clonal propagation, 70 Water, 108 F1 hybrid breeding, 70 How water loss from the leaf is controlled, 109 Wide hybridisation, 71 The mechanisms of stomatal opening and closure, 109 Somatic variation, 71 Water stress, 109 Somatic hybridisation, 71 The problem of drought, 110 Recombinant DNA technology, 72 Physical structures that help to conserve water, 111 Marker-assisted breeding, 72 Biochemical pathways that help conserve Genome sequencing, 72 water, 113 Genetic modification, 73 Contents vii

C-4 plants, 113 Germination, 144 Crassulacean acid metabolism, 114 Alternating temperatures and light, 144 Salinity, 115 Phytochrome, 145 Too much water, 115 Nitrate and smoke, 145 Aquatic plants, 117 Some practical considerations, 146 Watering in the garden, 117 Collecting seeds, and F1 hybrids, 147 Choosing plants for particular conditions, 117 Further reading, 148 Conclusion, 117 Authors and affiliations, 148 Further reading, 118 Authors and affiliations, 119 11 Vegetative propagation, 149 Summary, 149 9 Plants and seasons, 120 Introduction, 149 Summary, 120 Characteristics of vegetative propagation Introduction, 120 and its value to gardeners, 149 Day-length, 120 How plants regenerate, 150 Mechanisms for the control of flowering by day-length, Practical propagation, 154 124 Softwood cuttings, 154 Detection of day-length by the leaf, 127 Hardwood cuttings, 156 Chemical nature of the flowering signal, 128 Plant hormones and flowering, 129 Evergreen cuttings, 157 Formation of storage organs in response to day-length, Leaf cuttings, 157 131 Root cuttings, 158 Day-length and the control of leaf-fall Layering, 159 and dormancy, 133 Division, 160 Temperature, 134 Other organs, 161 Vernalisation, 135 Grafting and budding, 161 The advantages of vernalisation Micropropagation, 163 for a plant, 136 Conclusion, 164 Effective temperatures for vernalisation, 136 Further reading, 165 Devernalisation, 136 Authors and affiliations, 165 Direct effects of temperature on flowering, 136 Damage caused by sub-zero temperatures, 136 12 Size and form, 166 Breaking winter dormancy, 137 Summary, 166 Increasing temperatures, 138 Introduction, 166 Conclusion, 138 How size is controlled, 166 Further reading, 138 Endogenous factors, 166 Authors and affiliations, 138 External factors controlling size, 167 How form is controlled, 168 10 Growing plants from seed, 139 Summary, 139 External factors, 168 Introduction, 139 Form and size can be manipulated by Seed production and germination, 139 the gardener, 169 Recalcitrant seeds, 140 Pruning, 169 Seed storage, 141 Special training methods, 170 Dormancy, 142 Special forms, 171 Physiological dormancy, 142 Conclusions, 173 Morphological dormancy, 142 Further reading, 173 Physical dormancy, 143 Authors and affiliations, 174 viii Contents

13 Colour, scent and sound in the garden, 175 Seasonality, 202 Summary, 175 Climate, 203 Introduction, 175 Difference between climate and weather, 203 Colour in plants, 175 Global climatic zones, 204 The perception of colour, 175 UK climate influences, 204 Plant pigments, 176 Conclusion, 205 Pigments as attractants, 177 Further reading, 205 Variegation, 178 Authors and affiliations, 205 Chimeras, 178 Transposons, 178 15 Climate and other environmental changes, 206 Pattern genes, 178 Summary, 206 Viruses, 178 Global environmental change, 206 Tulipomania, 179 Changes in atmospheric composition, 206 Environmental factors influencing colour, 179 Climate change and climate variation, 208 Seasonal changes, 180 Changes in nutrient cycles, 211 The use of colour in the garden, 180 Other environmental changes, 212 Scent and flavour, 181 Conclusions, 213 Scent wheels, 184 Further reading, 213 Sound, 185 Authors and affiliations, 213 The nature, perception and appreciation of sound, 185 16 Protected cultivation, 214 Sounds for pleasure, 186 Summary, 214 Conclusion, 190 Why protect plants?, 214 Further reading, 190 What are the benefits?, 214 Authors and affiliations, 190 Temperature, 215 14 Climate and weather, 191 Development, 215 Summary, 191 Stem growth, 216 Introduction, 191 Cold tolerance, 217 Temperature, 192 Principles of protection, 217 Heat, 192 Energy transfer, 217 Cold, 193 The importance of light, 217 Hardiness, 194 Cladding materials, 218 Growing season, 194 Glass, 218 Soil temperature, 196 Film plastics, 218 Precipitation, 197 Bubble plastic sheets, 219 Impacts of rainfall, snow and hail, 197 Polycarbonate sheets, 219 Seasonality of precipitation, 197 Types of protection, 219 Extremes of rainfall, 197 Mulches, 219 Humidity, 198 Horticultural fleeces and meshes, 219 Wind, 198 Cloches and cold frames, 219 Nature and causes, 199 Tunnels, 220 Effects of wind, 199 Greenhouses, 220 Pressure, 199 Systems to be added, 222 Light, 200 Heating systems, 222 Day-length, 200 Ventilation, 222 Angle of the sun, 200 Energy saving, 222 Light intensity, 201 Carbon dioxide (CO2), 223 Sunshine hours, 202 Lighting, 224 Contents ix

Irrigation, 224 Weed problems, 245 Control systems, 225 Poisonous and irritant plants, 246 Biological control, 225 Conclusion, 247 Mechanisation, 225 Further reading, 247 Special cases, 225 Authors and affiliations, 247 Plant growth regulators, 226 Does protection have disadvantages?, 226 18 Controlling the undesirables, 248 Crops grown under protection, 227 Summary, 248 Chrysanthemum, 227 Introduction, 248 Cucumber, 228 Keeping out the undesirables, 248 Lettuce, leafy salads and other salad vegetables, 229 The role of the UK government, 248 Poinsettia, 229 The role of the horticultural industry, 249 Strawberry, 230 The role of gardeners, 250 Tomato, 231 Know your enemy, 252 Pot plants, 233 Control, 253 Conclusions, 233 Cultural practices (‘good gardening’), 253 Further reading, 233 Physical methods, 255 Authors and affiliations, 233 Host resistance or tolerance, 256 Biological control, 257 17 The diversity of the undesirables, 234 Chemical control, 259 Summary, 234 Conclusions, 261 Introduction, 234 Further reading and sources of information, 261 Pests, 234 Books, 261 Nematodes (eelworms), 234 Websites, 261 Molluscs: slugs and snails, 234 Authors and affiliations, 261 Mites, 234 Insects, 234 19 Maturation, ripening and storage, 262 Birds and mammals, 235 Summary, 262 Diseases, 235 Introduction, 262 Opportunists, 237 Changes in metabolism and ethylene synthesis, Necrotrophs: destructive parasites, 237 262 Biotrophs: non-destructive parasites, 237 Respiration and water loss, 262 Hemibiotrophs, 237 Ethylene, 263 Symptoms caused by the different types of pathogenic Maturation and ripening, 264 microorganisms, 237 Seeds, 264 Weeds, 239 Fruits, 265 Annual weeds, 239 Vegetables, 265 Perennial weeds, 239 Cut flowers, 266 Weed origins, 239 Pre-harvest influences on storage quality, 266 Useful weeds, 240 Diseases and disorders, 266 Intraspecific diversity, 241 Climatic factors, 267 New pests and diseases, 242 Field factors, 268 Deciding whether an organism is a problem, 243 Varietal factors, 268 When is a pest a pest?, 243 Harvesting, handling and preparation for storage, The importance of weather, 244 269 When to control pests, 244 Time of harvest, 269 When is a disease a problem?, 244 Handling, 269 x Contents

Post-harvest treatments, 270 Gardens and the wider environment, 295 The storage environment, 271 Wildlife in gardens, 295 Fresh produce, 271 Ecosystem services, 296 Low-temperature storage methods, 271 Conservation in gardens, 296 Controlled atmosphere (CA) storage, 272 Conservation of wild plants, 296 Seeds, 273 Conservation of cultivars, 297 Trends in commercial storage, 274 Conclusions, 298 Non-commercial storage, 275 Websites and further reading, 298 Seeds, 275 Websites, 298 Soft fruits, 275 Books, 298 Stone fruits, 275 Authors and affiliations, 298 Pome fruits, 275 22 Low-input and low-impact gardening, 299 Vegetables, 276 Summary, 299 Cut flowers, 276 Introduction, 299 Conclusion, 276 Conservation of resources in the garden, 299 Further reading, 276 Soil nutrients and organic matter, 299 Authors and affiliations, 277 Water management, 300 20 Garden ecology, 278 Recycling other materials, 302 Summary, 278 Wildlife, 302 Ecology and ecosystems, 278 Carbon and greenhouse gas emissions, 304 Ecology: open and closed systems, 278 The problem of peat, 305 Food webs, 278 Environmental footprint of lawns, 305 Nutrient and carbon cycling, 279 Cash benefit of low-intensity garden management, 306 Cycling at the global scale, 280 Conclusions, 306 Habitats, 282 Further reading, 306 Climate and soil tolerance, 282 Websites, 306 Natural processes and human land management, 283 Books, 306 Slow-growing and fast-growing plants, 284 Authors and affiliations, 306 Competition and herbivory, 286 23 Health, well-being and socio-cultural benefits, 307 Habitat creation, 286 Summary, 307 Biodiversity, 288 Gardens and ecosystem service provision, 307 Why are there so many plants?, 288 Why garden?, 307 Diversity and stability, 289 Gardens and green therapy, 309 Ecological succession and the balance of nature, 289 Restorative landscapes, 313 Unstable dynamics, 290 Horticultural therapy, 314 Conclusions, 290 Health risks, 315 Further reading, 291 Crime and antisocial behaviour, 316 Authors and affiliations, 291 Social and educational opportunities, 316 21 Garden wildlife and conservation, 292 Children and green space, 317 Summary, 292 Encouraging a balanced diet, 317 Natives and aliens, 292 Gardening and attitudes to the wider Gardens and native flora, 292 environment, 318 Native species and the Southwood hypothesis, 293 Conclusions, 319 Invasive plants and animals, 294 Further reading, 319 Contents xi

Author and affiliations, 319 The gardens of horticultural societies, 325 Private and small commercial gardens, 325 24 Gardens for science, 320 Universities and independent research institutes, Summary, 320 326 Introduction, 320 Conclusion, 328 Botanic gardens, 320 Further reading, 328 European origins and development in the United Authors and affiliations, 328 Kingdom, 320 Collections, 322 Glossary, 329 Research, 324 Conservation, education and training, 325 Index, 355

Preface to third edition

Previous editions of Science and the Garden have proved explore particular topics as and when it suits them, and very popular with students of horticulture and profes- for whom it is important that the individual chapters sional and amateur gardeners wishing to know more include sufficient background information to be read about the plants and practices that are the everyday cur- in isolation. Where we felt that a more complete un- rency of gardening. We hope that this new edition will derstanding of a particular topic could be obtained by satisfy these audiences and encourage others to learn consulting other chapters, however, we have provided more about a branch of science that is endlessly fasci- cross-references. nating and a vital adjunct to all good horticulture. We are most grateful to the many authors and il- In the third edition we have added new chapters on lustrators, mainly but not exclusively drawn from the Climate and other environmental changes (Chapter 15) and Science Committee and staff of the Royal Horticultural Health, well-being and socio-cultural benefits (Chapter 23). Society, past and present, for their hard work and com- Many of the other chapters have been completely re- mitment to this project, and for responding promptly written or extensively revised, often with new authors to the suggested changes to their initial manuscripts and/or illustrators, and the remainder have been care- or illustrations. This has allowed the whole enterprise fully updated and re-edited. We have renamed several to reach fruition on time. We thank Nigel Balmforth, of the chapters and have also taken the opportunity to Kelvin Matthews and other staff at Wiley-Blackwell for divide others or to move material from one chapter to their encouragement and professional help throughout anoth