Narcissus and Daffodil

Production of Narcissus bulbs 89
will be cropped because of the physical damage this causes, the likely spread of
disease, the loss of photosynthetic area and the high labor requirements, and
perhaps also because of contractual arrangements. Flower cropping may increase
the incidence of smoulder because of the opportunity for the fungus to invade
damaged surfaces (Gray and Shiel, 1975, 1987; Dixon, 1985, 1986).
On the other hand, de-heading crops may increase bulb production by removing
a sink to nutrients, and by eliminating decaying flowers that may encourage
fungal diseases. However, the results of trials have been variable. Thus, Wallace
and Horton (1935) reported instances of 40 and 103% greater yields of bulbs
when the flowers were not cut, whereas Allen (1938) reported only minor effects
of flower or flower stem removal on bulb yield. Grainger (1941) found that the
stem contributed little to bulb growth, and suggested it should be removed. Kalin
(1954, 1956) reported highest bulb yields after de-heading: yields were reduced by
3% when flowers were left intact or cropped half-way up the stem, by 5% when the
flowers were cropped at bud stage, and by 7% when cropped at full bloom.
Removing the flower bud as soon as the stem had grown enough to allow it gave
yields similar to those of de-heading. When these practices were repeated annually,
the effects were cumulative. De Vlugt and Kruijer (1975) confirmed similar
yield losses as a result of not de-heading (1%) or not picking flowers (5%). The
differences between different trials may be due to cultural practices, cultivars, location
or how carefully the cropping and de-heading treatments were carried out,
although, in the case of de Vlugt and Kruijer’s (1975) study, the results were
similar whether ‘careful’ or ‘commercial’ standards of removal were used. Some
cultivars have brittle stems, and large amounts of damage would be expected from
de-heading (Tompsett, 1976). Removing leaves at cropping, compared with cropping
flowers alone, further reduced yields by 66 and 36% when only one or two
leaves were left attached, respectively (Allen, 1938). Overall, de-heading is probably
not economically worthwhile. The removal of non-cropped flower heads is
recommended in the Netherlands to control fire, but, although de-heading
machines have been tested, this is not usually practised (van Aartrijk, 1990).
Whether flowers are cropped, de-headed or left intact, a fungicide spray programme
is important for different reasons.
Irrigation
Trials have shown that bulb yields are best in soils near field capacity (Strojny,
1975; Goniewicz et al., 1976). A rise in soil moisture over the range 40–95% of
available water capacity had no effect on N, P or K levels in the bulbs, but levels of
P and K in the roots rose with increasing moisture levels (Dabrowska, 1975).
Water availability also altered root anatomy and stomatal numbers in narcissus
(Goniewicz et al., 1976).
In the Netherlands, irrigation of bulb crops in sandy soils is normal, often
through the control of the water table. It is recommended that narcissus should be
irrigated when it becomes difficult to squeeze the soil round the roots into a ball,
and water should be applied in applications of 15–20 mm, as higher applications
damage soil structure. Narcissus crops are not usually irrigated in the UK,
although some trials have shown that irrigation increases the yield of larger bulbs,
especially at higher planting rates (ADAS, 1985d). Moderate irrigation may improve