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 1 st 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 follow­ing their use.

Contents

List of Tables

Preface to the first edition

Preface to the second edition

Acknowledgements

1 Loam or loamless media?

1.1 Loam composts 1.2 Loamless mixes 1.3 Lightweight mixes with some mineral soil

2 Materials for loamless mixes

2.1 Peat 2.2 Bark 2.3 Other organic materials 2.4 Minerals 2.5 Plastics

3 Physical aspects

3.1 Physical terminology 3.2 Bulk density and total pore space 3.3 Water relations 3.4 Aeration of substrates 3.5 Formulating mixes 3.6 Wettability of mixes 3.7 Compaction

4 Principles of nutrition

4.1 Cation exchange capacity 4.2 Anion exchange capacity 4.3 Availability of nutrients: loam v. loamless mixes 4.4 Chemical analysis of lightweight media

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page xiii

xvii

xix

xxi

1

3 4 4

6

6 21 28 32 36

40

40 42 44 48 53 59 61

64

64 67 68 70

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 death points 248

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CONTENTS

12.2 Methods of heat pasteurization 12.3 Steam 12.4 Steam-air mixtures 12.5 Flame pasteurizer 12.6 Electrical pasteurizers 12.7 Other methods 12.8 Chemistry of heat pasteurization 12.9 Rules for heat pasteurization

13 Chemical sterilization

13.1 Soil fumigants 13.2 Soil fungicides

• 13.3 Soil insecticides

14 Plant containers, modules and blocks

14.1 Clay v. plastic pots 14.2 Paper and peat pots 14.3 Modules and blocks

Appendices

1 Metric conversions 2 Imperial and us capacity measures 3 Illumination and solar radiation units 4 Atomic weights 5 Formulae and molecular weights of some commonly used

chemicals 6 Formulae and molecular weights of some chemicals commonly

used to supply microelements 7 Chemical gravimetric conversions 8 Temperature conversions

Bibliography

Index

xii

Page 250 250 254 255 257 259 259 264

265

265 267 269

271

271 276 277

284

284 285 285 286

286

286 287 287

288

301

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

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UST OF TABLES

4.12 Interpretation of salinity readings by the Dutch 1 : 1.5 volume extract and the English 1 : 6 volume extract. page 92

5.1 The range of dry weights and nitrogen contents of some pot and bedding plants 96

6.1 Effect oHorms and rates of superphosphate on the mix pH, determinations made in 0.01 M CaCl2 123

6.2 The loss of phosphorus from peat-sand mixes by leaching 127 6.3 Comparison of superphosphate and slow-release phosphorus

fertilizers in powder and granular forms 129 6.4 The relative neutralizing values of various liming materials 135 6.5 Comparative mineral values of an average peat and an average mineral

soil, % by weight 144 6.6 Nutrient analysis of the fertilizers commonly used in preparing

loamless mixes 147 6.7 Effect of fertilizers on the soil salinity 148 6.8 Suggested levels of macroelements in the tissues of certain ornamental

plants (% by weight of dry tissue) 150 6.9 Macroelements that can be applied as foliar sprays 150 7.1 Microelement content of some Scottish peats 152 7.2 Weights of boron salts required to prepare stock solutions to give

0.5 p.p.m of boron after dilution at 1 partin 200 156 7.3 Response of lettuce, cv. Kwiek, to molybdenum added to the seed

sowing and potting mixes (fresh weights in g) 158 7.4 Effect of soil pH on the colour and aluminium content of hydrangea

flowers 163 7.5 Effect of nitrogen source and pH on microelements in the leaves of

chrysanthemums grown with frit 253A at a rate of 1. 75 g 1-1 165 7.6 Weight of inorganic salts to supply microelements to peat-based mixes 169 7.7 Examples of proprietary microelement fertilizers used in soil-less

potting mixes 169 7.8 The microelement content of fertilizers 170 7.9 Average microelement content of phosphorus fertilizers in the USA

(from Bingham 1959) 171 7.10 Conditions affecting availability of microelements in mixes 172 7.11 Average rnicroelement ranges found in the leaf tissue of ornamental

plants 172 7.12 Microelements that can be applied as foliar sprays 173 8.1 Effects of superphosphate rates and slow-release fertilizer sources on

the percentage of phosphorus in the tissue and the total plant dry weight of three species of ornamental plants 188

9.1 Liquid feed strengths for constant feeding 203 9.2 Solubility of fertilizers in cold and hot water 206 9.3 Weight of fertilizers in grams required to prepare one litre of stock

solution for dilution at 1 in 200 to give a range of liquid feeds 207 9.4 Weight of fertilizers in ounces to make 1 gal (Imperial) of stock solution

for dilution at 1 in 200 to give a range of liquid feeds 208

xiv

LIST OF TABLES

9.5 Weight of fertilizers in ounces to make 1 us gal of stock solution for dilution at 1 in 200 to give a range of liquid feeds page 209

9.6 Preparation of liquid feeds from complete NPK water-soluble fertilizers (based on us gal) 213

9.7 Nutrient concentrations in p.p.m. and meq I-I supplied by fertilizers at either 100 g per 1000 1 or lIb per 1000 us gal. 213

9.8 Comparison of nutrient concentrations in p.p.m. (or mg 1-1) and mEql-1 214

9.9 The applied weight of fertilizer (lb of 20% nitrogen fertilizer per 1000 ftz) resulting from different combinations of the strength of feed and the amount of irrigation (Biamonte 1977) 214

9.10 Equivalent rates of irrigation over a range of pot sizes 215 9.11 Control of media pH of pot chrysanthemums by liquid fertilizer

formulation 221 9.12 Suitability of water for irrigating pot plants (from Waters et al. 1972) 225 10.1 Air-water relations of three mixes irrigated by different systems 233 11.1 Particle size fractions on which the mechanical analysis of soil is based 239 11.2 Growth of Erica gracilis in different composts 246 12.1 Rates of steam and air flow required to treat 1 m 3 of medium in 30 min

(50% heating efficiency assumed) (Aldrich et al. 1972) 255 12.2 Manganese toxicity risks 262 12.3 Effect of the pasteurizing temperature on the release of manganese 263 14.1 Mean evaporative water loss from fallow plastic and clay pots 272

xv

Preface to the first edition

The past two decades have seen rapid advances in the technology used to produce pot plants. Glasshouses designed and orientated to give maxi­mum light transmission, fully automatic heating and ventilating systems, carbon dioxide enrichment of the atmosphere, controlled photoperiods using automatic blackouts and incandescent lamps which enable plants such as chrysanthemum to be flowered at any time of the year, mist propagation techniques, chemical growth regulators which control the height of plants, automatic watering and feeding systems, etc.: these are only some of the developments which have transformed pot plant culture.

There have also been many changes in the composts and systems used to grow the plants. Mineral soils, which formed the basis of the John Innes composts, are now either too expensive or too difficult to obtain in suitable quality and sufficient quantity. Consequently the grower has been forced to seek other materials such as peat, perlite, vermiculite, plastic foam, shredded bark, etc. New types of fertilizers, new methods of heat sterilization and new chemical sterilizing agents are also being used.

As with many industrial processes, an alteration to improve one part of a process often means that alterations to other parts of the process are required in order to make the whole operation successful; so too with the new composts. By changing the bulky materials from which the compost is made, a different emphasis must be given to the type and quantity of base fertilizers used, and also to the watering and liquid feeding. Com­posts made with these new materials give results that are equal or even superior to those obtained from the traditional composts, providing that their individual characteristics and requirements are understood. The use of these new composts should be regarded as a new system of growing, rather than a simple change of compost.

The purpose of this book is to provide horticulturists, including stu­dents, growers, advisory officers and those who simply grow plants for pleasure, with information on the characteristics of the new materials, how they can be used to make composts and for the subsequent nutrition of the plants. Much of the information given is based on previously unpublished studies made by the author at the Glasshouse Crops Research Institute over the last fifteen years.

xvii

Preface to the second edition

In the decade since the first edition there has been no slackening in either the rate of annual growth in the volume of container media used, or in the number of research reports published. The numbers of plants that are grown in small volumes of media, either for the whole of the cropping period or for transplanting, continues to increase. For example, in 1984 50% of the greenhouse tomato crop in the UK was grown in peat bags or modules rather than in the border soil. Also in 1984, 76.2 million hardy ornamental nursery stock plants were grown in containers, whereas the amount in 1974 was only 19.8 million.

The economic advantages obtained from raising vegetable transplants in peat blocks, 'Speedling' or 'Hassy' type modules, and bedding plants by the plug system, have stimulated research into media and growing techniques suitable for these systems.

In western Europe peat continues to be the most important of the materials used for making growing media. There is now an increasing awareness of the need to maintain a physical balance between the water-holding capacity of media and their air-filled porosity, either by using young, fibrous, 'white' peats or by adding physical conditioners such as bark, perlite or grit where natural aeration is insufficient.

In regions where peat is unavailable or uneconomic, greater attention has been given to the use of local materials such as bagasse, coconut fibre, peanut hulls, etc. The use of shredded bark is probably the best example of research turning a waste product, that is not only potentially toxic to plants but also has special nutritional characteristics, into a suitable growing media.

Chapters have been rewritten, extended or revised, depending upon the extent of recent developments in the areas covered. The purpose of the book remains the same.

xix

Acknowledgements

I am grateful to the many colleagues, at home and overseas, for their helpful suggestions in the preparation of this edition. In particular I wish to thank Miss M. A. Scott and Mrs C. King (ADAS) for advice on nursery stock mixes, Dr Pauline M. Smith (GCRI) for guidance on chemical steriliza­tion and fungicides, also Mr E. W. Johnson (ADAS) and Mr P. Adams (GCRI) for helpful comment on liquid feeding. Details of potting media and practices used in other countries were supplied by Dr H. R. Gislemd (Norway), Mr D. G. Nichols (Australia) and Dr M. Prasad (New Zealand); Professor F. A. Pokorny supplied information on the pre-treatment and use of bark mixes in the USA.

I have also benefited from many useful discussions on various aspects of container media with Professor J. L. Paul and Dr D. R. Hershey at the University of California, Davis; and with Mr R. L. Jinks at GCRI. Many of the lines of research that have proved both interesting and rewarding to pursue have resulted from discussions with grower friends in the glasshouse and nursery stock industries.

Grateful acknowledgements are given to the publishers and the authors for permission to reproduce Figures 2.2 and 4.12. Figure 2.5 is reprinted by permission of Vapo Oy, and Figure 2.6 by permission of Bord Na Mona.

xxi