Growing Dutch Iris Under Glass

The early outdoor forcing of the Dutch hybrids under frames, Ganwicks and barn cloches is widely carried on by commercial growers to supply the early spring markets. The same methods may also be used to provide early bloom for the home. All the Dutch varieties will bloom well under outdoor glass and will come into bloom three weeks in advance of uncovered bulbs.

The varieties Wedgwood and Yellow Queen are also suitable for indoor cultivation in gentle heat and like all the others may also be used for cool glasshouse flowering. By using a slightly heated house, followed by the early-flowering varieties under glass outdoors, it is possible to have Dutch iris for cutting from late February until the Spanish varieties come into bloom in June, a six-months’ display for a few shillings. As these iris are essentially flowers for cutting rather than for pot culture in the Growing Dutch Iris Under Glasshome, no word will be made of home cultivation under this heading. That is reserved for the dwarf-flowering species.

Where cloches and frames are to be used, the beds should be planted to the width of the glass covering. Where possible, a trench should be prepared, a 4-in. Space being left at the top which will give the plant the extra height, for it is little use covering the bulbs and then having to remove the glass before they have come into bloom unless Dutch lights are available with which to cover the plants when the cloches have ceased to play their part. If the lights are placed on their sides and held in place by wooden stakes and over the top are also placed lights, a miniature greenhouse will have been made which will provide the correct height for Dutch irises.

The bulbs are planted early in October and are covered early in February, the plants coming into bloom in April when advantage may be taken of the Easter market, if it is a late Easter. If a cool or heated greenhouse is to be used, the bulbs are planted either in large pots or deep boxes. They should be planted about September 1st into a mixture of loam, coarse sand and well-rotted manure. Old mushroom-bed manure is ideal, so are spent hops. Some lime rubble should also be added. As many as six bulbs may be planted into each large pot, or if growing in boxes, plant them 2 in. apart each way. A 10 – 12cm. bulb should be used.

After planting and watering, the pots and boxes are stood outside in a plunge bed of ashes or sand until thoroughly rooted, which will take about two months. The first batch may then be taken indoors. Wedgwood will be the first and a temperature of just under 50 F. will be sufficient, indeed a temperature above 52 F. will be detrimental to the production of a top-quality flower. Only when the buds are showing should the temperature be increased to 55 F. At this period, the bulbs will need ample supplies of water and a dry, well-ventilated atmosphere. Wedgwood taken indoors about November 1st should be ready for cutting when grown in a temperature of 50 F. by March 1st. Later batches of Yellow Queen and Imperator will be taken indoors before the year end and will be in bloom from the end of March. Those outdoors under lights or cloches will bridge the gap until the unprotected Wedgwood is ready.

Iris may also be grown in a quite cold house by planting in pots or boxes as described which are taken indoors when the tomato crop has ended in late October, or the bulbs may be planted directly into the greenhouse-floor border in October. In this case, they should be covered with sacking to keep out the light until early December, when they should be rooted. They should at no time be over-watered and will be in bloom early in April. Owing to their occupying the greenhouse for some considerable time when planted in this way, planting in pots or boxes is preferable.

DUTCH IRIS VARIETIES

  • Blue Triumphator. A superb variety and not one commonly grown. The blooms are of a pure heavenly blue colour, delicately perfumed. The 7-8 cm. bulbs are fairly inexpensive and should be used lavishly.
  • Golden Harvest. This is the rich yellow iris plentiful in florists’ shops during May.
  • H. C. van Vliet. Having deep navy blue standards and sky-blue falls, the colour effect is most striking.
  • Imperator. The most widely grown of all Dutch iris, the colour is indigo-blue.
  • Jeanne d’Arc. A superb new variety of strong constitution, the bloom being of a rich Jersey cream shade.
  • Lemon Queen. A fairly recent introduction and a beauty, the pale lemon-coloured blooms being of a large size.
  • Professor Blaauw. A new variety, the blooms being of a rich shade of gentian blue.
  • Wedgwood. Although always classed as a Dutch hybrid, this is really a hybrid of Iris Tingitana. It is pale blue flowered and useful in that it is the earliest of all this section and the most important glasshouse iris.
  • White Superior. Bears a large bloom of purest white, the fall petals having a deep yellow stripe making up a most attractive flower.
  • Yellow Queen. Rich uniform yellow. With Wedgwood the best variety for indoor cultivation.

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