MEDIA AND MIXES FOR CONTAINER-GROWN PLANTS

Transcription

1 MEDIA AND MIXES FOR CONTAINER-GROWN PLANTS

2 TITLES OF RELATED INTEREST Growing media for ornamental plants and turf K. A. Handreck and N. D. Black University of New South Wales Press

3 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

4 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 , 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 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 ISBN (ebook) DOl / Potting soils. 2. Plants, Potted. 3. Greenhouse management. I. Bunt, A. C. Modem potting composts. II. Title. S589.8.B '86-dc CIP Typeset in 10 on 11 point Palatino by Paston Press, Loddon, Norfolk

5 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.

6 Contents List of Tables Preface to the first edition Preface to the second edition Acknowledgements page xiii xvii xix xxi 1 Loam or loamless media? 1.1 Loam composts 1.2 Loamless mixes 1.3 Lightweight mixes with some mineral soil Materials for loamless mixes 2.1 Peat 2.2 Bark 2.3 Other organic materials 2.4 Minerals 2.5 Plastics 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 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 ix

7 CONTENTS 4.5 Nutrient uptake by the plant page Acidity (ph) Lime requirement Soluble salts 86 5 Nitrogen Nitrogen and pot plants Forms of mineral nitrogen Slow-release forms Choice of fertilizer type Nitrogen and peat Other macroelements Phosphorus Potassium Calcium Magnesium Sulphur Slow-release fertilizers Mineral soil and peat comparison Nutrient and environment interactions Fertilizer analysis and salt index Plant mineral levels Foliarfeeding Microelements Boron Copper Manganese Molybdenum Iron Zinc Chloride Aluminium Fritted microelements Chelated microelements Inorganic salts and proprietary fertilizers Other sources Microelement availability Foliar sprays 173 x

8 CONTENTS 8 Mix formulation and preparation page Historical Denmark Finland Germany Ireland Netherlands Norway United Kingdom United States of America Hardy nursery stock Azalea mixes Protea mix Proprietary formulations Mix preparation Liquid feeding Principles of feeding Formulating liquid feeds Practical aspects of feeding Injection equipment Quality of irrigation water Irrigation systems Drip system Capillary watering Flooded benches Overhead sprinklers John Innes composts Formulation Compost ingredients: loam Peat Sand Pasteurization Characteristics and use Composts for ca1cifuge plants (JIS (A» Other loam-based mixes Heat pasteurization Thermal death points 248 xi

9 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 Page xii

10 List of tables 2.1 Peat areas and production page Peat textural grades and particle sizes The von Post scale for measuring peat decomposition Composition of three peats (percentage of total organic matter) Properties of sphagnum peat Recommended particle size distribution for pine bark and hardwood bark Element composition of softwood barks and a sphagnum peat Average percentage of carbon released as carbon dioxide from woods and barks over 60 days Total and 'extractable' amounts of nickel, zinc, chromium and copper found in sewage sludges Dry weights and porosity of some potting mix materials Approximate relationships between units used to measure soil water tension Approximate root aeration requirements of selected ornamentals, expressed as the free porosity Gohnson 1968) CEC of a sedge peat at three ph values determined by four methods (from Haynes 1982) Cation exchange capacities of some materials and mixes 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) 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 Standards for nitrogen, phosphorus, potassium and magnesium in the 1: 1.5 volume extract (Dutch method) Standards for ammonium nitrogen, nitrate nitrogen, phosphorus, potassium and magnesium in the 1: 6 volume extract (English ADAS method) Desirable indices for crops (English ADAS method) Standards for nutrients determined by the saturated media extract ~~ % 4.9 Desirable nutrient balance in saturated media extract Sulphur-containing materials that can be used for acidification Interpretation of salinity readings determined by the saturated media extract and 1 : 2 volume methods 92 xiii

11 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 The range of dry weights and nitrogen contents of some pot and bedding plants Effect ohorms and rates of superphosphate on the mix ph, determinations made in 0.01 M CaCl The loss of phosphorus from peat-sand mixes by leaching Comparison of superphosphate and slow-release phosphorus fertilizers in powder and granular forms The relative neutralizing values of various liming materials Comparative mineral values of an average peat and an average mineral soil, % by weight Nutrient analysis of the fertilizers commonly used in preparing loamless mixes Effect of fertilizers on the soil salinity Suggested levels of macroelements in the tissues of certain ornamental plants (% by weight of dry tissue) Macroelements that can be applied as foliar sprays Microelement content of some Scottish peats Weights of boron salts required to prepare stock solutions to give 0.5 p.p.m of boron after dilution at 1 partin Response of lettuce, cv. Kwiek, to molybdenum added to the seed sowing and potting mixes (fresh weights in g) Effect of soil ph on the colour and aluminium content of hydrangea flowers Effect of nitrogen source and ph on microelements in the leaves of chrysanthemums grown with frit 253A at a rate of g Weight of inorganic salts to supply microelements to peat-based mixes Examples of proprietary microelement fertilizers used in soil-less potting mixes The microelement content of fertilizers Average microelement content of phosphorus fertilizers in the USA (from Bingham 1959) Conditions affecting availability of microelements in mixes Average rnicroelement ranges found in the leaf tissue of ornamental plants Microelements that can be applied as foliar sprays 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 Liquid feed strengths for constant feeding Solubility of fertilizers in cold and hot water 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 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

12 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 Preparation of liquid feeds from complete NPK water-soluble fertilizers (based on us gal) Nutrient concentrations in p.p.m. and meq I-I supplied by fertilizers at either 100 g per or lib per 1000 us gal Comparison of nutrient concentrations in p.p.m. (or mg 1-1) and meql 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) Equivalent rates of irrigation over a range of pot sizes Control of media ph of pot chrysanthemums by liquid fertilizer formulation Suitability of water for irrigating pot plants (from Waters et al. 1972) Air-water relations of three mixes irrigated by different systems Particle size fractions on which the mechanical analysis of soil is based Growth of Erica gracilis in different composts 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) Manganese toxicity risks Effect of the pasteurizing temperature on the release of manganese Mean evaporative water loss from fallow plastic and clay pots 272 xv

13 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

14 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 % 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

15 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 Figure 2.5 is reprinted by permission of Vapo Oy, and Figure 2.6 by permission of Bord Na Mona. xxi