COLOUR VARIATIONS IN HYDRANGEAS

Otago Witness, Issue 4039, 11 August 1931, Page 63

COLOUR VARIATIONS IN HYDRANGEAS

For many years the instability of colours in hydrangeas has been a difficult problem, and the cause of much disappoinmtent to gardeners in all parts of the world.

Whereas the white varieties are con stant, the pink and blue colours are elusive in the extreme. Plants purchased, or cuttings taken from plants carrying either of these colours frequently change from pink to blue or vice versa when planted in different soils. Various reasons have been advanced from time to time, but not one had any scientific basis. One writer declared that if blue was required the plants should be grown in the shade. Another curious fact was that cuttings taken from the plant which had. changed colour would return to its original shade when planted in conditions similar to that from which the cuttings had been taken in the first place. To add still further to the difficulty, some plants grown from either a pink or blue parent would produce blooms of both colours on the one plant in the one season. Science is often too busy to bother with problems which do not concern man’s immediate need of daily bread, but in this instance a scientist investigated the difficulty with gratifying results. It is now comparatively easy for a grower to get blue or pink blooms to order, and to intensify both, more or less at will. The story of the investigation is taken from the official report of the scientific proceedings of the Royal Dublin Society, Vol. XVII, Nos. 20-24, page 201. The paper was read bv Mr W. R. G. Atkins. 0.8. E., Se.D., FJ.C., on March 27, 1923. Before outling the brief history of the experiments it is advisable to explain that just as temperature is measured by a thermometer and expressed in “ degrees ” “ Fahrenheit ” or “ Centigrade,” so- soil acidity is determined by chemical means and the hydrogenation concentration of soil is expressed in degrees of which “ pH ” is the symbol. Taking pH7 as a starting point of neutrality, the lower the figure the greater the degree of acidity, while above pH7 the higher the figure the greater the degree of alkilinity. Briefly it may be expressed as follows :— pH4—Very acid. pH5 —Acid. pIIO —Moderately acid. pH7—-Neutral. pH8 —Moderately alkaline. pH9—Alkaline. pHlO—Very alkaline. From this table it will also be readily gathered that acid and alkali are opposites, and to correct acid an alkali is used and vice versa. The first test was to determine the condition of various soils in different localities, and the following table shows the result:—

There is in these examples undoubted proof of the relation between soil rcacttion and flower colour. They include the case of a plant originally bearing blue flowers changing to pink when in an alkaline habitat, as at Cornwood, and the converse change, pink to blue and some pinkish, at Templemichael. Some plants bear blue and pink flowers; these are found in situations with a reaction of pH7.5 and under. It must be added that the soil tested was from the first four inches, which is insufficient to get near the obsorbent portions of the roots. Since the change of colour occurs in the petals, it was felt, however, that definite proof was necessary to show the condition of the sap soluble colour pigments in the blooms themselves. It was known that in other flowers there were definite changes in colour values according to the condition of the sap For instance, a red rose retains its pure red colour only so long as the sap is acid; as soon as the sap becomes neutral or alkaline the purple or bluish shades at once become apparent. Ac-

cordingly . pink and blue flowers were treated with dilute acetic acid, but the pink did not change to blue as expected. As a matter of fact, there was no apparent change due to the treatment. A further test was carried out by which pink and light mauve or blue flowers were gathered from a single plant. By chemical means both colours were tested and showed pH4.O, or strongly acid conditions in both eases. These tests clearly indicated that some other agency was responsible for the variation in hydrangea colour. Taking a cue from the old gardening practice of adding rusty nails to the potting soil to produce blue flowers, the next test dealt with the solubility of iron salts in the flowers themselves. Pink blooms were cut and placed in dilute solutions of iron salts. It was noticed that a deep dark green appeared in the stems, and spread slowly into the. veins of the flowers. The flowers then died, apparently from being placed in too strong a solution. Sufficient result, however, had been obtained to encourage the investigations to continue this line of thought. After reviewing all the experimental work of other scientists, it was decided to demonstrate if possible the difference between the iron content of blue as against pink blooms. Without wearying the average reader with exacting chemi cal formulae, blue and pink flowers were selected all from the one plant. The first test showed a very definite presence of iron in the blue flowers, and a corresponding absence of iron in the pink. In order to make doubly sure, a further test was made by different methods, when it was found that the blue flowers contained 140 parts per million of iron, while the pink only showed about 60 parts per million. The author of the paper then outlined in exhaustive detail the question of the availability of iron salts in the soil. Very briefly summarised it may be stated as follows:—When the soil is in an acid condition ample iron salts aie available for absorption by the plant, which will., then produce blue flowers. When, however, the soil is alkaline, the iron becomes more or less insoluble, and because the plant cannot take it up, very little iron enters into the petal sap and pink blooms are therefore produced. If the results obtained in Dublin, Devon, and Cornwall are again studied, it will be noted that the results are in perfect harmony with the summary outlined above. The next step is to apply the theory to garden practice. In respect of hydrangea colour the gardening public is roughly divided into two classes. First, those whose plants flower blue but who want pink, and secondly, those who obtain pink without effort but who desire blue. The first-named may take it for granted that there is ample iron and acid in their soil. To produce pink hydrangeas it is necessary to select a potting medium in -which iron is as far as possible absent. In addition, it will probably be necessary to place the plants in a wooden tub or container. A suitable soil may be made from pure sand and thoroughly well decayed cow manure and leaf mould. If the water used is not heavily loaded with iron, the desired pink blooms should be realised. Another method suggested for trial is to lime the soil liberally round established plants in order to render the natural iron in the soil insoluble. For those requiring blue where pink is the rule, the plants should be treated with sulphate of iron either applied direct to the soil or used as a liquid manure. The quantity used must be determined by each grower according to his own particular conditions, as much more would be required in limestone soils than in sandstone country. Care must be taken not to overdo this chemical, as an overdose may easily cause trouble. A dessertspoonful to four gallons of water or a small handful crushed and very lightly spread round the plant may be used as a starting point, and increased or reduced according to results. It may be noted as a matter of interest that the writer’s own experience bears out in a very decided way the scientific theory outlined by Mr Atkins. In the last few years a large number of new hydrangeas have been imported from England. On arrival they were planted in a heavy ironstone soil which shows an acid reaction. The first year's flowers all proved true to English descriptions, and many beautiful red and pink colours were produced.—Harry 11. Hazlewood, hi the Garden Lover.

Locality. Colour of Hydrangea. pH of Soil. Notea. Cornwood, Devon .. . .Blue .. . 6.0 (slightly acid) Several plants. ..Pink .. . 7.6 (neutral) One plant, blue when in previous site. Plymouth IToo .. .. ..Pink .. . 8.0 (alkaline) Several plants, various sites. Falmouth, near sea ..Pink .. . 7.5 (neutral) Ono plant. Mt. Edgcumbe, CornwallBlue .. . Numerous plants blue. Mt. Edgeumbe. Cornwallpink and BIuo ,. ..5.3 (acid) Ono plant. Dublin '..Pink .. . 8.0 (alkaline) One plant. Antony, Cornwall .. ..Pink; some termcdlate blue and in-7.3 (neutral) Two plants. Templemichael, Co. Blue, pink and inter-6.2 (slightly acid) Plant when bought and Waterford .. .. .. mediate . planted had bright pinkflowers only.