Growing Iris Bulbs
Planting Iris Bulbs
In the last few years the growing of irises under glass has become a major greenhouse crop, particularly as with preparation they can be induced to flower for a major part of the year. Of the numerous species, the main varieties for greenhouse growing have been selected from the Xiphium and Xiphiodes groups which are natives of the Mediterranean zone.
The embryo bud contained in the iris bulb is incompletely developed when the bulbs are lifted, and the development of the bud continues under cool storage at 8.9°C (48°F) or planted in cool.
Bulbs for forcing should usually be from 10cm upwards, uniform in size and should not have producedthe previous season. Out of season flowering of suitable varieties can be achieved by a combination of heating and cooling, this procedure being generally carried out by the supplier.
`Wedgwood’ varieties and sports
Planting: mid autumn to late winter.
Flowering: mid winter to spring (treated bulbs flower earlier)
All other varieties
Planting: late autumn — mid-winter.
Flowering: mid-winter to early /mid-spring
Plant outdoors in beds or greenhouse borders early spring—late summer.
Flowering: mid-summer to mid-autumn or later under cover Iris danfordiae (yellow) and I. reticulata (blue) are grown in pots, planting early in the year to flower in spring, 3-4 bulbs per 15cm (6in) pot.
Irises can be grown either in boxes, pots or borders, in all cases with sufficient depth of soil 10-12.5cm (4-5in) to accommodate the root system. Any good garden soil with good texture and a pH of 6, and reasonably well supplied with nutrients, will suffice. The addition of peat is frequently necessary totexture. For forcing, plant very shallowly about 7.5cm (3in) apart; for slower growing plant deeper 5-7.5cm (2-3in). For planting between late spring and late summer mulch the ground with damp peat to keep soil temperatures cool.
It is usually recommended that for ‘Wedgwood’ and its sports 13.3-15°C (56 — 59°F) should be given for the first two weeks, maintaining or slightly raising the temperature at night to 17.8°C (64°F) to advance flowering. For other varieties give 11.1-12.2°C (52-54°F) for first two weeks, up to 13.3°C (56°F) for smaller bulbs (7-8 and 8-9cm). Coolness and ventilation is the general rule to avoid gross production of foliage and possible ‘blindness’ (when the flowers do not form). Support may be needed with nets or canes.