Agriculture Reference
In-Depth Information
dropped as internet platforms pointed out that the repellent effect is not as clear as
promised. However, these example show clearly that customers buy plants not only
for ornamental value but also for other novelty purposes such as being a repellent.
Production requirements
To meet production requirements and to introduce a
plant successfully requires an understanding of plant growth and development that
includes methods to control growth, flowering and form manipulation so as to suit
the market. For example, in the US, rose production is geared around Valentine's
Day. These techniques are gained through a combination of experience and scien-
tific endeavour. It also requires practical knowledge of the growing requirements,
soil or potting media, temperature, light and shade regulation.
Ability to flower
This depends on the environmental factors driving the phenologi-
cal (vegetative/flowering) phases. Plants varying in their photoperiodic require-
ments regulate their flowering response to day length. This process is complex and
can involve sensitivity to infra-red signalling (Weller et al.
1997
). In addition plants
may have specific temperature requirements which determine the rate at which
flowering occurs. Flowering can also be promoted by application of hormones and
fertilisers. This will allow early flowering to be synchronised to produce flowers
ready for a special calendar day, such as Mother's day. Plants are either short-day
(less than 12 hours), day-neutral or long-day (14 to 16 hours). For example, flow-
ering in Qualup bell (
Pimelea physodes
) under short-day conditions (10 hour day
length) can be promoted by a cool pulse for 2 weeks at 10/15°C followed by warm
temperatures (24/12°C) (Seaton and Plumber
2004
). This technique can then be
used also for
P. ferruginea.
Another example is the marigolds which are obligate
short-day plants requiring day length shorter than a certain critical length to flower
with some being facultative flowering faster with shorter days. Whereas the snap-
dragon, sunflower, salvia, and petunia are considered long-day annuals, other plants
such as the zinnia are day-neutral with flowering not being affected by day length.
There can be considerable variation in photoperiod response between cultivars and
the grower needs to recognize the response of individual cultivars to match display
and location requirements. For many bedding plants the use of black cloth may be
necessary to initiate flowering. Other techniques available are to produce plants
ready for planting by providing black cloth in the case of short-day plants supple-
mentary high pressure sodium lights (HPS) if plant plugs are grown during win-
ter in heated glasshouses during the last 2 weeks before transplanting (Cox
2009
).
Research has shown that there can be side effects of supplementary lighting such
as extension growth which may need to be controlled to retain plant compact form.
Plant form
Having the right shape of plant is critical to the range of uses plants
can be put to in the landscape. Plant form such as height and bushiness can be
manipulated by chemical application, pruning and pinching strategies. For example
Geraldton wax, which is normally grown as a cut flower producing long stems, can
be shortened and made more bushy with more flowers per plant by application of
the growth inhibitor paclobutrazol (if permitted) while cytokinin 6-benzylamino-
purine (if permitted) can reduce plant height but does not increase flower numbers
(Seaton et al.
2007
). Other approaches are to manipulate plant gibberellin biosyn-
thesis genetically to control plant height (Bhattacharya et al.
2010
).
