The bulb is a whole plant consisting of leaves, scales, flower, tunic, basal plate, bud of
a daughter bulb, and an offset bulb. The scales are modified fleshy white leaves attached
to a thick basal plate which sheath the central bud. From the basal plate, both the roots
and the stem of the flower emerge. The tunic is a protective covering of the bulb consisting
of dry leaves, white, brown, or black in color and of smooth or reticular consistency.
There are approximately 35 genera of bulbous plants and the most important genera are Allium,
Iris, Lilium, and Tulipa. There are other bulbous plants which have corms instead of bulbs.
Corms look like bulbs but are morphologically different. Corms consist of bud, old stem, tunic,
basal plate, roots, and food store. There are about 21 genera possessing corms of which
Gladiolus is perhaps the most popular genera. Bulbous plants are important greenhouse crops
in temperate regions. In the United States and Canada, flower bulbs are forced and marketed
as either potted plants or cut flowers.
The procedure for forcing bulbs follows a consistent pattern with relatively minor changes
across species. As soon as they become available (late August or early September), bulbs are
stored in a cool environment (13 oC). As temperatures fall, they are placed in containers in
a rooting room, covered with a suitable growing media, and soaked with water until they develop
a profuse rooting system capable of absorbing water and nutrients. At this stage, the bulbs
are ready to flower and if brought into a warm environment will rapidly grow and bloom.
Lilies
Lilium longiflorum Thunb is a white trumpet lily species from the southern islands of Japan.
In its original habitat, the lily grows at annual temperatures of 21 oC with minimum
temperatures of 12 oC in January and maximum temperatures above 30 oC in July. Japan produces
the bulk of lily bulbs used in Europe and the United States for either cut flower or pot
production.
Studies on the temperature requirements of lilies indicate that air and soil temperatures of
24 oC favor rapid leaf unfolding, stem elongation, and flower expansion with concomitant
depletion of primary (bublet) scales. After flower buds are visible, soil temperatures have
no appreciable effects on their rate of expansion while air temperatures are the controlling
factor.
The bulk of the lily demand occurs during the Eastern holiday season. Therefore, a good
understanding of how the lily responds to temperature is critical to manipulate plant
development so plants flower just prior Eastern. Temperature strongly affects stem elongation
and bud development rate, particularly from visible bud stage until anthesis. A cubic model
is often used to describe bud development rate as a function of temperature from 14 to 30 oC
while a linear model describes bud development rate as function of temperature from 14 to
21 oC. Based on the linear model, the base temperature for bud development (at which
development rate is zero) is 3.5 oC and the bud development rate is reported to be 0.05 cm
per day for each 1 oC increase in average daily temperature.
Mature bulbs are a prerequisite for successful manipulation of plant development.
Lily bulbs are mature when they force rapidly and predictably after low temperature storage.
In lily bulb production, bud removal is a customary practice to obtain large bulbs. Large and
heavy bulbs are sold at higher prices than small bulbs primarily because upon forcing large
bulbs tend to produce more flowers than small bulbs. The effectiveness of bud removal depends
upon the time of removal. Flower buds can be removed when the length of the largest bud is
about 1.0 cm (early removal) or 3.5 cm (late removal). Early bud removal usually stops
pedicel growth, inhibit stem elongation, and reduce total leaf area but does not affect
bulb weight. Late bud removal does not affect either plant height but increases both fresh
and dry bulb weights by 15%. Early bud removal causes 81% of the daughter bulbs to sprout
prematurely compared to 27% for late bud removal.
Tulips
Tulips are originated from the Mediterranean region, North and Central Asia, East China,
and Japan. Tulips were introduced first to Europe in 1554. Today, modern tulips are grown
worldwide in the temperate regions and are classified into as many as 23 groups. The first
three groups (Duc van Tol tulips, single early tulips, and double early tulips) constitute
the "Early Flowering" tulips all of which can be forced. The next two groups (Mendel and
Triumph tulips) constitute the 'Mid Season Flowering' tulips, all of which can be forced.
Groups 6 to 15 are the "Late Flowering" tulips of which Cottage tulips are suitable for
forcing. Groups 16 to 23 are not normally forced.
Commercial forcing of tulips encompasses three distinct phases which are related to the
developmental cycle of the bulbs. The initial phase includes bulb harvest, floral initiation,
and organo genesis at warm temperatures (17 to 20 oC). After the flowers are fully formed, a low
temperature period is required prior to anthesis. Bulbs are then brought into warm temperatures
where flower stalk elongation and anthesis occur.
Recommended temperatures for forcing tulips usually range from 13 to 18 oC.
The manipulation of forcing temperatures can have a great impact on growth and flowering.
For example, day and night temperatures above 18 and 14 oC, respectively reduce the length of
the forcing period. Forcing temperatures can be used to some extent to control the market
characteristics of tulips. Cooler days and warm nights tend to reduce plant height, which
are desirable in pot production, while warm days and cool nights cause plants to be taller
and therefore better suited for cut flower production.
Gladiolus
The name gladiolus is derived from the Latin word gladius, which means sword, referring to
the shape of the leaves. Gladiolus flowers are funnel shaped, usually flaring and ruffled,
sometimes hooded, and almost always are carried in a one sided spike.
The genera Gladiolus (family Iridaceae) comprises about 180 species found throughout Africa
and the Mediterranean area. The modern gladiolus are hybrids of species found in the
Mediterranean region, tropical and South Africa, and the Mascarene Islands. They are tall
(stems up to 120 cm with individual blooms as thicker as 20 cm) with self colored flowers
(white, white and cream, light yellow, orange, light salmon, deep salmon, scarlet, light red,
deep red, or black red, light rose, deep rose, lavender, lavender with shading, purple,
light violet, deep violet, smoky shades, and other shades).
Gladiolus is propagated from cormels which grow in clusters on stolons between mother and
daughter corms. Cormels are usually graded into three sizes: large (> 1 cm in diameter),
medium (0.6 to 1 cm), and small (< 0.6 cm). Large cormels are customarily used for commercial
production.
Gladiolus is very sensitive to water stress showing a differential response between corm
and flower growth. No effects of irrigation frequency are reported on corm size but flowering
is greatly reduced from 84% when carnations are irrigated every 9 days to 55 % when irrigated
every 18 days.
Gladiolus generally tolerates high light and temperatures but flower abortion and reduced
floral bud occur under short days, low light regimes, and cool night temperatures. The crop
is especially sensitive at the two leaf stage, which is approximately the time of bud
initiation.
Several factors including the media, weather, and history of previous nutritional status of
the mother corm influence the nutrient requirements of gladiolus. As a general rule, gladiolus
requires NPK applications of 90 to 135, 40 to 80, and 91 to 150 kg/ha, respectively.
References
Manrique, L.A. 1993. Greenhouse crops: A review. J. Plant Nutrition 16:2411-2477.
Manrique, L.A. 1994. Technology for greenhouse systems. Manrique International Agrotech,
Honolulu, HI. 263p.
Luigi's
P.O. Box 61145
Honolulu, HI 96839
Phone: (808) 285-3128 (cell)
Phone: (808) 732-4986
http://www.lava.net/manrique/luigi.htm
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