Narcissus and Daffodil

Production of Narcissus bulbs 97
etc., and it is important that drying does not continue to the point of excessive
weight loss or desiccation.
Bulb storage
Once dry, bulbs are often stored at ambient temperatures in sheds, but it is preferable
to store them at 17–18 °C: lower temperatures can slow development and can
render the bulbs susceptible to HWT damage, while higher temperatures favour
the development of base rot. The ambient summer temperature of the region
needs to be considered in deciding whether controlled temperature storage is
likely to be cost-effective. Bulb storage is in effect an extension of second-stage
drying, and free movement of air around the bulbs is essential in controlling
moulds and re-rooting. When bulbs are in trays or have already been transferred
to net bags, no forced ventilation may be needed, but where they are held in bulk
bins, continued use of fans will be needed, if only for part of the day. During this
phase, bulbs can be extracted for cleaning, grading, etc.
Little information is available on the harmful effects of ethylene on narcissus
bulbs. Hitchcock et al. (1932) reported that concentrations as low as 1.5 ppm
(0.75 ppm for ‘Paper White’) retarded leaf and stem elongation, while 3 ppm or
more caused a variety of leaf and bud distortions. Hydrogen fluoride can cause
leaf scorch as an air pollutant (Spierings, 1969).
If bulbs are kept at high humidities above 30 °C, soft rot due to Rhizopus species
can reduce narcissus bulbs to a musty mass. This can occur in the transit of bulbs
or in propagation during the incubation of ‘chips’ (see below).
Cleaning, inspecting and grading
Once dry, bulbs are usually passed along a line involving the removal of loose
skins and soil by vibrating riddles, brushes and dust extractors, bulb splitting and
removal of damaged and diseased bulbs by hand, grading over a series of riddles,
and collection and packing of different grades of bulbs. At all stages of bulb handling
mechanical damage, which could lead to bruising, infection or poor appearance,
should be minimised by reducing drops or cushioning surfaces. Trials with
drops of 25 cm have shown that narcissus bulbs are susceptible to damage in the
first 10 days after lifting and later, in autumn, and damage was increased by subsequently
storing bulbs at ambient temperatures rather than at 17 °C (Schipper,
1971). Mechanical damage to the base plate can result in infection by the base rot
fungus (Gregory, 1932; Hawker, 1935). Some studies, however, failed to show a
correlation between simulated mechanical damage and the later development of
bulb rots (Millar, 1978).
When grading narcissus bulbs, it is usual to bump bulbs along a series of slotted
riddles of progressively larger sizes. Because narcissus bulbs are often asymmetrical
or flattened on one side, round riddles (as used with tulip bulbs, for example)
are considered unsuitable. Although other grades may be used, narcissus bulbs are
often graded in 2 cm-wide bands, bulbs of 12–14 and 14–16 cm grades being used
for sales and smaller and larger grades being used as re-planting stock (some
cultivars have relatively small bulbs and other grades may apply). Machines for
counting and weighing bulbs are available. Graded narcissus bulbs for sale are