A HANDBOOK OF GARDEN IRISES, DYKES 1924

A HANDBOOK Ol GARDEN IRISES By W R DYKES, M.A., L.-es-L Secretary of the Royal Horticultural Society Author of "The Genus Iris," etc LONDON: MARTIN HOPKINSON COMPANY LTD 14 HENRIETTA STREET, COVENT GARDEN, W.C 1924 £ff : Frontispiece I Polyhymnia, a Regeliocydus hybrid (I Korolkowi x susiaaa) (Two-thirds size) Printed xn Great Britain PREFACE Some apology is a third book on perhaps needed for the production of My excuse is that of the two Irises former volumes the earlier and smaller has long been out of print while the large monograph was written primarily from the botanical and not from the horticultural point of view The small book did not aim was rather a rapid survey of Irises as garden plants and the fact that it was written in the space of a long week-end at the time of the Coronation of 191 is evidence that it was at describing all the species It never intended to be exhaustive The Genus tions of some Iris with its life-size, fifty species, known and full coloured illustrabotanical descrip- was the result of an enquiry into the botany of Irises and of an attempt to cultivate all the available species and to raise them from seed The present volume is intended for gardeners, though it is hoped that the information as to the distribution tions of all the of the various species, species, the speculations as to their and the botanical details which in certain cases must be understood in order to separate closelyallied species will prove no less welcome than the hints as to their cultivation, which are the results of an experience of some twenty years affinities |51S0ft^ PREFACE vi Each section of the genus is treated as a whole in a separate chapter and the short descriptions of the individual species, which follow, must be read in conjunction with This method necessarity involves it a certain amount of repetition but without it it would hardly be possible to deal with each section as a whole No attempt is made to describe each species in minute detail, in all its parts or to give its exact distribution herbarium specimens in the various museum collections For this information the It is hoped, howreader is referred to the Genus Iris by reference dried to enough information is given about all the species, which are at all adequately known, to enable them to be recognized and cultivated with some chance ever, that of success The treatment of the innumerable garden hybrids has necessarily been more difficult and probably may seem more inadequate than that of the species It is obviously impossible to describe every one and equally difficult to decide which are the best varieties or those most worthy of description list compiled to-day will necessarily Moreover, any be largely out of date a few years hence It was no easy matter to obtain illustrations for a book of these dimensions, could be hfesize satisfactory and for scarcely Photographs of any Irises of them are seldom and of In the end it was the cost of coloured drawings their reproduction was prohibitive decided to use as illustrations a series of drawings in monochrome by Miss E Kaye In most cases these have been drawn direct from the living plant, but in PREFACE vii a few instances, where living plants were not available was able, by the kindness of the late Hon N Charles Rothschild, to use specimens from an at the time, she admirable series of coloured drawings of the Europe by F H Round The Round's drawings were used, are I I variegata, xiphium, I I sibirica, xiphioides, I cases, I in aphylla, Irises of which Mr I pallida, spuria (flower stem only), and I juncea might be thought that a key should have been given which would enable any one who was totally It ignorant of Irises to identify any species have spent much time in attempting to construct such a key but have come to the conclusion that it would necessarily be so intricate as to be of little I use to the beginner I have, therefore, merely given at the end of Chapter II, page II, a key to the various sections of the genus and inserted in the general observations on each section a key to the species which compose it CONTENTS page Preface I II V The parts of the Iris flower and plant The various sections of the Genus and their distribution III The geographical distribution of the various sections and species and their relative IV The Nepalensis Section The Gynandriris Section The Reticulata Section The Juno Section The Xiphium Section The Evansia Section The Pardanthopsis Section The Apogon Section The Sibirica Subsection The Spuria Subsection The Californian Subsection The Longipetala Subsection The Hexagona Subsection ages V VI VII VIII IX X XI XII XIII XIV XV XVI XVII I 13 21 24 27 41 62 78 87 89 90 102 113 122 127 Miscellaneous Beardless Irises The Oncocyclus Section The Regelia Section The Pseudoregelia Section The Pogoniris Section 130 150 164 Garden Bearded 220 A Irises NOTE on cultivation, ON RAISING SEEDLINGS AND ON Diseases A Table of times of planting and flowering A list of Synonyms sometimes used in Gardens Index 175 180 235 240 246 247 LIST OF ILLUSTRATIONS I THE 236 IRIS be carefully scratched away from the base of the leaves and then it is usually quite easy to see whether roots are being formed to move the large, fleshy root-growth Iris and they If it is are, it new should be safe only the species that form rhizomes that will stand removal when is The more not active slender species perish before they can take hold of the soil again This accounts for the fact that we seldom see such so ideal rock garden plants as cristata, pumila, ruthenica Yet if these are moved, broken up and replanted at the right time, they are capable of forming clumps which flower so freely as literally to doing really well hide the foliage Nearly all Irises are the better for sun and very few need shade, though a few will tolerate what gardeners call half-shade, such are gracilipes, cristata, vema, foetidissima and, I am inclined to think, tectorum Seeds must not be coddled and too great kindness in the shape of them warmth and protection They should always be sown never under glass Sir Michael Foster A is likely to kill in the open and few weeks only before his death, wrote to tell me that a hybrid had just germinated after lying ground for eighteen years and I have raised plants from seeds more than ten years' old Under glass they would certainly have rotted However, it must not be supposed that all Iris seeds lie Oncocyclus seed dormant in the dormant for ten years Fresh seeds of species should germinate readily in the first spring after they are sown, approximately at the time when plants of the several species begin to grow again Hybrid seeds THE RAISING OF SEEDLINGS are more irregular and 237 in particular those of the On- cocyclus species Protection is, however, useful once the seeds have germinated and every endeavour should then be made to get the young plants to grow rapidly so that they may To be planted out as early as possible allow them to become crowded in the seed pots and the roots to become matted checks them considerably Planting out seedlings is less toilsome when the ground is wet but not wait for rain Dig a few holes where the plants are to go with a heavy trowel and fill three or four with water then put a seedling in each before all the water has soaked away and draw ; the earth up leave the surface loose and dry much less planting This should to the base of the leaves rapid than Evaporation is then the plants are watered after if This cakes the surface of the soil and 33 and See also pp 48, 189 After planting no further attention will be needed assists evaporation except occasional weeding and loosening of the surface soil Seedling plants will continue to grow until late autumn and, except in very severe seasons, remain more or less green throughout the winter The foliage of estabUshed plants of most Bearded Irises tends to die away in the autumn and the dead in the leaves should be to aUow removed from time the rhizomes to be as dry as possible no circumstances should short while they are tidy to time in order still Unless the leaves Iris Under leaves ever be cut off make them rhizomes the from away come green in order to quite easily, they should be allowed to remain In THE 238 IRIS the case of some Beardless Irises, such as I sibirica, the leaves, though dead, stay attached until the spring but they may, in this case, and with advantage, be shortened in the autumn to about one third of their length Iris Diseases There are four distinct diseases which not quently attack our garden One which Irises Irises of the Reticulata Section is infre- attacks caused by the fungus Mystrosporium adusium and the treatment given on page 32 for this is Rhizome Rot iridis causes is caused by a bacillus Pseudomonas which mostly attacks the base of the stem and it to collapse, usually appearing when the flowers are just This disease can be recognized at once by its characteristic smell, the rhizome becoming soft and slimy The best treatment is to lift the plant attacked and carefully cut away all diseased portions of the rhizome It should then be washed in a bright pink solution of potassium permanganate, replanted in fresh soil and sprinkled with superphosphate This should be washed in with water dry An ounce or two if of lime the weather is of superphosphate to the square yard, scattered over beds of Bearded Irises at flowering time, should check the disease and at the same time provides the plants with the lime that they need Care should be taken to apply the superphosphate when the leaves are dry, for otherwise The other two it will stick to them diseases are Leaf Spot which attacks the leaves of Irises, especially in wet autumns, and the IRIS DISEASES 239 Rust which seems to occur most frequently on Regelia and Regehocyclus Irises and sometimes to spread to ordinary Bearded varieties Leaf Spot, which is due to Heterosporium gracile, appears as pale, round or elliptical spots on the leaves, which gradually become more numerous until they cover The leaves then die away the whole of the surface prematurely and the rhizome is consequently weakened This disease is rarely found on soil in which there is plenty of lime and the best remedy is to scatter slaked rarer Leaf lime over the surface of the beds in the autumn after removing as much as possible of the dead and dying foliage Beds for Bearded Irises can scarcely have too much old mortar rubble added to them and, when this is done, Iris Leaf Spot should not be troublefirst some The rust, Puccinia iridis, appears as small reddishbrown rusty spots and the remedy is to spray at intervals of two or three days either with a solution of one ounce of potassium sulphide in two or three gallons of water or with ammoniacal copper carbonate The latter is prepared by dissolving three solution ounces of sulphate of copper and three ounces of carbonate of soda in a quart of concentrated ammonia, which is then diluted with twenty-two gallons of water THE 240 O z w o h-H-M CO W o w o ^ o W 8^ •n TD CD ^ ^ o C >- c3 ^ g -*j -*-» en «- ^ ^ c^ "ex: O *i « « •sips o H CO « Q < w MMMM MHM •31 fe o o o o St 00 o 00 o, a, r-j(_,l-iUI-(C/)l-i(-i X! XI H^^ XI -l-> ba^ +-" -4-1 ^ -Q M^ -Q -M -M r>,-l-> -)-> o o Xo O O OJ O O O XI e o -4-J -'-' -l-> 00 So o : I Vl^ a a *-> Xo x^ a X £x3 ^x s_g a a s s a; i coSScoOc/5coScn< « iJ « «U Q M - crt •-1 :3 ^ D •-1 Di S M e s V-I a, ] CO >H HJ :^p£;s:^s s-< ii