Agriculture Reference
In-Depth Information
Harvesting and handling
Cut flowers are harvested at various bud development
stages. For example, single daffodil blooms are typically
harvested at a tight bud stage. Geraldton waxflower, which
is a spray-type bloom, is harvested at a stage when 25% of
flowers have opened (Beal
et al
. 1998a). Bud-stage flowers
must be of sufficient horticultural maturity that they have
the inherent capability to open in the vase.
Ideally, flowers should be harvested during a cool part of
the day so that their metabolic rate is low and removal of field
heat is less difficult. Harvesting is most often by hand with
the aid of secateurs (Figure 19.8). Harvested blooms need
protection from dehydration. Protection is usually afforded
by shading with covers and use of handling solutions, such as
chlorinated water. Flowers also need protection from physical
damage and thus careful manipulation. Transport to the
packing shed should be rapid and gentle. Hampers and
conveyors are useful aids. In some circumstances flower are
prepared for sale and packed in the field.
maturity, bud and flower form, leaf condition and pest and
disease damage (Figure 19.8). Grading can be assisted
with mechanical and electronic devices such as photocell-
based stem length graders. Image analysis is also being
investigated for grading.
Bunching can either be of single or mixed varieties of
one or more species. Length-graded flowers are usually
bunched on the basis of stem numbers (e.g. five- or ten-
stem bunches). Weight can also be used, either alone or
along with stem numbers. Uniformity of bunches is an
important consideration. Conveyors are used widely in the
preparation of large numbers of mixed-flower bunches.
Flowers are added incrementally to the bunch as it moves
along the packing line. Mechanical or electronic balances
are used to check bunch weights. Bunches are very often
tied with rubber bands. Tying machines that use elastic
string are also used.
Bunches are trimmed to length using a guillotine or saw.
Frequently, especially for high-value flowers and mixed
bouquets, bunches are sleeved. Sleeves are usually printed
plastic and are sometimes perforated. They are typically
used with a chute feed-type dispenser.
Cooling
Cut flowers have relatively high metabolic rates and
therefore benefit from rapid cooling to their optimum
holding temperature (Joyce 1988; Nowak & Rudnicki
1990; Nowak
et al
. 1991; Wills
et al
. 1998; Reid 2002,
2004; Tables 19.1 and 19.2). Cooling from 20°C to 0°C
decreases respiration rate of carnations to about 4% of that
at 20°C (Table 19.1).
Flowers can be cooled soon after harvest, to remove
field heat, and/or after grading, post-harvest treatments and
packaging (Figure 19.7). Most flowers are cooled to close
to 0°C, except tropical flowers and foliage such as orchids,
ginger, anthurium and bird of paradise (Table 19.2). Once
flowers have been cooled, it is advantageous to keep them
cool wherever this is practical.
Room cooling is suitable for cut flowers since they have
a high surface area to volume ratio and can be stood in
water to prevent drying out. However, pressure or forced-
air cooling is best for packaged flowers provided that
airflow among the blooms in not obstructed (Figure 19.8).
Again, because of their high surface area to volume ratio
and ability to rapidly rehydrate, vacuum cooling is a good
method for cut flowers. For details of cooling methods see
Gross
et al
. (2004) and Kader (2002).
Pre-treatments
Pre-treatments are treatments applied to cut flowers, by
growers, wholesalers or exporters, prior to storage or
dispatch with the objective of maximising post-harvest
longevity.
Hydration
Maintenance of a high water vapour pressure in the
atmosphere surrounding cut flowers reduces their propen-
sity for water loss. The vapour pressure deficit (VPD) is the
difference in vapour pressure over free water inside cut
flower tissues and the vapour pressure in the surrounding
atmosphere (Wills
et al
. 1998). VPD is largely a function
of relative humidity and temperature. A low VPD is usually
achieved by keeping flowers at high RH (e.g. >95%) and
low temperature (e.g.
ca
. 2°C). High RH in the immediate
vicinity can be achieved using low water vapour transfer
wraps, such as polyethylene shrouds and sleeves, placed
over individual bunches or groups of bunches. Atmospheric
RH may be increased by steam or mechanical humidifiers.
Wet coil rather than conventional dry coil refrigeration
systems are particularly suitable in cold rooms for cut
flowers (Wills
et al
. 1998). However, high RH can also be
achieved by selection of a dry coil refrigeration system that
has a large surface area evaporator coil and which therefore
operates at a low temperature differential. Maintaining a
low airspeed over cut flowers also reduces water loss
Grading
Culling is often the first of the packinghouse operations,
whereby defective blooms (e.g. bent stems) are rejected.
Grading is usually to length, although other quality attri-
butes also need to be considered. These attributes include
