MEDIA AND MIXES FOR CONTAINER-GROWN PLANTS TITLES OF RELATED INTEREST Growing media for ornamental plants and turf K. A. Handreck and N. D. Black University of New South Wales Press MEDIA AND MIXES FOR CONTAINER-GROWN PLANTS (second edition of Modern potting composts) A manual on the preparation and use of growing media for pot plants A. C. BUNT N.D.H.(Hons), M.1. BioI. Formerly with the Glasshouse Research Institute, Littlehampton, Sussex London UNWIN HYMAN Boston Sydney Wellington © A. C. Bunt, 1976, 1988 Softcover reprint of the hardcover 1s t edition 1988 This book is copyright under the Berne Convention. No reproduction without permission. All rights reserved. Published by the Academic Division of Unwin Hyman Ltd 15/17 Broadwick Street, London WI V IFB, UK Allen & Unwin Inc., 8 Winchester Place, Winchester, Mass. 01890, USA Allen & Unwin (Australia) Ltd, 8 Napier Street, North Sydney, NSW 2060, Australia Allen & Unwin (New Zealand) Ltd in association with the Port Nicholson Press Ltd, 60 Cambridge Terrace, Wellington, New Zealand First published in 1976 as Modern potting composts Second edition 1988 British Library Cataloguing in Publication Data Bunt, A. C. Media and mixes for container-grown plants: a manual on the preparation and use of growing media for pot plants. - 2nd ed. 1. Plants"Potted 2. Compost I. Title II. Bunt A. C. Modem potting composts 635.9'65 SB418 ISBN 978-94-011-7906-5 Library of Congress Cataloging-in-Publication Data Bunt, A. C. Media and mixes for container-grown plants: a manual on the preparation and use of growing media for pot plants/A. C. Bunt. - 2nd ed. of Modem potting composts. p. em. Bibliography: p. Includes index. ISBN 978-94-011-7906-5 ISBN 978-94-011-7904-1 (eBook) DOl 10.1007/978-94-011-7904-1 1. Potting soils. 2. Plants, Potted. 3. Greenhouse management. I. Bunt, A. C. Modem potting composts. II. Title. S589.8.B86 1987 635.9'86-dc 19 87-15332 CIP Typeset in 10 on 11 point Palatino by Paston Press, Loddon, Norfolk NOTE TO READERS To assist the reader in the presentation of information, trade names of products have sometimes been used. This constitutes neither endorsement of named products nor criticism of those unnamed. Every attempt has been made to check the accuracy of the various media formulae, and no liability can be assumed follow ing their use. Contents List of Tables page xiii Preface to the first edition xvii Preface to the second edition xix Acknowledgements xxi 1 Loam or loamless media? 1 1.1 Loam composts 3 1.2 Loamless mixes 4 1.3 Lightweight mixes with some mineral soil 4 2 Materials for loamless mixes 6 2.1 Peat 6 2.2 Bark 21 2.3 Other organic materials 28 2.4 Minerals 32 2.5 Plastics 36 3 Physical aspects 40 3.1 Physical terminology 40 3.2 Bulk density and total pore space 42 3.3 Water relations 44 3.4 Aeration of substrates 48 3.5 Formulating mixes 53 3.6 Wettability of mixes 59 3.7 Compaction 61 4 Principles of nutrition 64 4.1 Cation exchange capacity 64 4.2 Anion exchange capacity 67 4.3 Availability of nutrients: loam v. loamless mixes 68 4.4 Chemical analysis of lightweight media 70 ix CONTENTS 4.5 Nutrient uptake by the plant page 76 4.6 Acidity (pH) 79 4.7 Lime requirement 82 4.8 Soluble salts 86 5 Nitrogen 94 5.1 Nitrogen and pot plants 94 5.2 Forms of mineral nitrogen 97 5.3 Slow-release forms 105 5.4 Choice of fertilizer type 111 5.5 Nitrogen and peat 117 6 Other macroelements 120 6.1 Phosphorus 121 6.2 Potassium 131 6.3 Calcium 133 6.4 Magnesium 135 6.5 Sulphur 138 6.6 Slow-release fertilizers 139 6.7 Mineral soil and peat comparison 143 6.8 Nutrient and environment interactions 144 6.9 Fertilizer analysis and salt index 146 6.10 Plant mineral levels 149 6.11 Foliarfeeding 150 7 Microelements 151 7.1 Boron 153 7.2 Copper 156 7.3 Manganese 157 7.4 Molybdenum 158 7.5 Iron 159 7.6 Zinc 161 7.7 Chloride 162 7.8 Aluminium 163 7.9 Fritted microelements 163 7.10 Chelated microelements 166 7.11 Inorganic salts and proprietary fertilizers 168 7.12 Other sources 170 7.13 Microelement availability 171 7.14 Foliar sprays 173 x CONTENTS 8 Mix formulation and preparation page 174 8.1 Historical 174 8.2 Denmark 175 8.3 Finland 176 8.4 Germany 177 8.5 Ireland 178 8.6 Netherlands 179 8.7 Norway 179 8.8 United Kingdom 180 8.9 United States of America 182 8.10 Hardy nursery stock 187 8.11 Azalea mixes 192 8.12 Protea mix 196 8.13 Proprietary formulations 196 8.14 Mix preparation 197 9 Liquid feeding 201 9.1 Principles of feeding 201 9.2 Formulating liquid feeds 205 9.3 Practical aspects of feeding 219 9.4 Injection equipment 222 9.5 Quality of irrigation water 223 10 Irrigation systems 229 10.1 Drip system 229 10.2 Capillary watering 231 10.3 Flooded benches 233 10.4 Overhead sprinklers 234 11 John Innes composts 235 11.1 Formulation 235 11.2 Compost ingredients: loam 236 11.3 Peat 241 11.4 Sand 241 11.5 Pasteurization 241 11.6 Characteristics and use 243 11.7 Composts for ca1cifuge plants (JIS (A» 247 11.8 Other loam-based mixes 247 12 Heat pasteurization 248 12.1 Thermal deathp oints 248 xi CONTENTS 12.2 Methods of heat pasteurization Page 250 12.3 Steam 250 12.4 Steam-air mixtures 254 12.5 Flame pasteurizer 255 12.6 Electrical pasteurizers 257 12.7 Other methods 259 12.8 Chemistry of heat pasteurization 259 12.9 Rules for heat pasteurization 264 13 Chemical sterilization 265 13.1 Soil fumigants 265 13.2 Soil fungicides 267 • 13.3 Soil insecticides 269 14 Plant containers, modules and blocks 271 14.1 Clay v. plastic pots 271 14.2 Paper and peat pots 276 14.3 Modules and blocks 277 Appendices 284 1 Metric conversions 284 2 Imperial and us capacity measures 285 3 Illumination and solar radiation units 285 4 Atomic weights 286 5 Formulae and molecular weights of some commonly used chemicals 286 6 Formulae and molecular weights of some chemicals commonly used to supply microelements 286 7 Chemical gravimetric conversions 287 8 Temperature conversions 287 Bibliography 288 Index 301 xii List of tables 2.1 Peat areas and production page 8 2.2 Peat textural grades and particle sizes 12 2.3 The von Post scale for measuring peat decomposition 13 2.4 Composition of three peats (percentage of total organic matter) 15 2.5 Properties of sphagnum peat 19 2.6 Recommended particle size distribution for pine bark and hardwood bark 22 2.7 Element composition of softwood barks and a sphagnum peat 22 2.8 Average percentage of carbon released as carbon dioxide from woods and barks over 60 days 23 2.9 Total and 'extractable' amounts of nickel, zinc, chromium and copper found in sewage sludges 29 2.10 Dry weights and porosity of some potting mix materials 39 3.1 Approximate relationships between units used to measure soil water tension 46 3.2 Approximate root aeration requirements of selected ornamentals, expressed as the free porosity Gohnson 1968) 49 4.1 CEC of a sedge peat at three pH values determined by four methods (from Haynes 1982) 66 4.2 Cation exchange capacities of some materials and mixes 67 4.3 Percentage of added nutrients found by chemical analysis of a mineral soil compost Gohn Innes) and a peat-sand mix (based on extracts using water or Morgan's solvent) 68 4.4 Percentage of added nutrients recovered in one litre of leachate from peat-sand (3: 1) and peat-vermiculite (1: 1) mixes, in I-litre pots 69 4.5 Standards for nitrogen, phosphorus, potassium and magnesium in the 1: 1.5 volume extract (Dutch method) 74 4.6 Standards for ammonium nitrogen, nitrate nitrogen, phosphorus, potassium and magnesium in the 1: 6 volume extract (English ADAS method) 74 4.7 Desirable indices for crops (English ADAS method) 75 4.8 Standards for nutrients determined by the saturated media extract ~~ % 4.9 Desirable nutrient balance in saturated media extract 76 4.10 Sulphur-containing materials that can be used for acidification 85 4.11 Interpretation of salinity readings determined by the saturated media extract and 1 : 2 volume methods 92 xiii