Chrysanthemums
The genera Chrysanthemum (family
Compositae) comprises over 150 species. The species from
which the present chrysanthemum cultivars mostly originate appear to be Chrysanthemum indicum
and Chrysanthemum morifolium. Oriental in origin, chrysanthemums have been a symbol of Chinese
and Japanese cultures for several centuries.
Introduced to Europe in the late 1600s,
chrysanthemums were brought to France in 1789, to England in 1795 and to the United States
in the early 1800s. Since then its commercial cultivation has dramatically increased. In
recent years, however, as orchids and roses are more popular, chrysanthemum production has
steadily declined but the crop is still the flower of choice of many people.
Under optimum conditions, the number of weeks from bud initiation to flowering is relatively
constant for chrysanthemums. This physiological response is used as a criterion to group
chrysanthemums as (i) early (9 weeks from bud formation to flowering), (ii) mid season (10
weeks), and (iii) late (11 weeks). The type of flower produced is also a criterion to
classify chrysanthemums as (i) incurved (the florets are all regularly incurved so that
the bloom takes the shape of a globe), (ii) reflexed (the outer florets curve downwards
while the inner ones tend to incurve), (iii) incurving (the petals are incurved giving
a sort of mop head), (iv) anemone flowered (the disk florets form a central mass of tubes
giving a pin cushion effect), (v) pompons (bedding type small button like flowers) and (vi)
singles (flowers with a central disk and no more than five rows of outside ray florets).
Optimum night temperatures for chrysanthemums are about 16 oC, although evidences indicate
that the crop can grow at 6 oC. Fast development occurs either at day and night temperatures
of 20 and 16 oC, or at constant temperatures of 20 oC. From a practical standpoint, extreme
temperatures should be avoided as high temperatures seem to increase pedicel length and delay
flowering while low temperatures appear to either prevent bud formation or delay flowering,
decrease leaf number and promote basal rosetting, reduce inter-node length and increase
flower diameter.
Day temperatures are more important than night temperatures for chrysanthemums. High day
temperatures (18 oC) apparently result in earlier flowering and taller stems but do not
influence flower number and final total fresh weight. High night temperatures (18 oC), in
turn, result in earlier flowering, more flowers, and reduce stem and leaf weight.
Short periods at suboptimal temperatures are reported to be beneficial for chrysanthemums.
For instance, overall growth, number of blooms and buds, and weights of blooms apparently
increase when chrysanthemums grow at 16 and 10 oC split temperatures.
Flowering is controlled by day-length (i.e., short days stimulate flowering while long days
stimulate vegetative growth) but the number of days to flowering varies with cultivars and
temperature regimes. Chrysanthemum superbum Bergmans cultivars usually flower on days longer
than 13 h although evidences show that some cultivars require periods of cold temperatures
(4.5 oC) or long days, or both and some require neither.
Carbon dioxide enrichment is customarily used to enhance chrysanthemum growth. In a study on
the effects of CO2 levels (330, 1,000, and 1,600 mg/kg) and photosynthetic flux densities
(44, 129, 260, and 395 umol/m2/s), shoot dry weight increased from 27 to 60% due to the
CO2 enrichment while shoot length, number of leaves, and growth of lateral breaks were all
increased by CO2 and light. No significant effects were obtained CO2 increased from 1,000
to 1,600 mg CO2/kg.
Chrysanthemums grow well in growing media including bark , soil , peat , sawdust , peat lite,
and most recently rock-wool. When compared with commercial mixes (i.e., Ball Growing Mix II
and Metro Mix 350), rock-wool based media amended with dolomitic limestone, gypsum,
phosphoric acid, potassium nitrate, and calcium nitrate produce plants of nearly equal size
and fresh weight but with fewer flowers of lower quality than those from commercial mixes.
In terms of water supply, chrysanthemums grow best when the soil water tension is below 30
kPa. Drip irrigation alone or drip plus controlled release fertilizer have been
successfully used in the production of good quality chrysanthemums. In fact, compared
with sprinkler irrigation, 70 to 80% water savings stem from the use of controlled release
fertilizer plus drip irrigation.
Carnations
The carnation (Dianthus caryophyllus) is native of southern Europe. The history of the
carnation goes back to 300 years B.C. when Theophrastos named the genera Dianthus, from
the Greek dios, divine, and anthos, flower. The specific name, caryophyllus (derived from
the Greek caryon, nut, and phyllon, leaf) was taken from the clove tree (Caryophyllus
aromaticus) and applied to carnations because of the clove like fragrance of its blooms.
Plant propagation of carnations is customarily done by cuttings, i.e., cuttings are taken
from flowering stems, cut about halfway between the swollen joints, and rooted in growing
media. The rooting usually takes 3 to 4 weeks. Prior to the propagation, cuttings are
usually stored at temperatures of 0 to 1 oC. Some studies have shown that storing cuttings
at temperatures above 0 oC (i.e., at 14 oC for 12 days) actually accelerates rooting. The
storage at higher temperatures and for longer periods, on the other hand, increases the
incidence of root rot diseases such as Fusarium.
Light appears to strongly influence the carnation. Low light regimes apparently result in
lower growth rates, reduced dry matter production, delayed flower and leaf initiation, and
increased leaf number. Evidently light exerts such an influence that carnation production
at high latitudes is not feasible without supplemental light. Studies on the effects of
light sources on carnations grown under 8 h periods of sunlight followed by a 16 h dark
period indicate that (i) continuous 16 h light was superior to short light periods in
hastening flowering while intermittent light was as effective as continuous light, (ii)
except for far red light, which was most effective immediately after the 8 h light period,
short light periods were most effective if given in the middle of the dark period, and (iii)
incandescent light was, at all times, superior to cool white or red fluorescent light. Other
studies indicate that flowering increase as the duration of the light period increase, and
that incandescent light is superior to cool white fluorescent light in 6 h night breaks.
On the effects of CO2 enrichment on carnations, a 37% increase in flower production occurs
when CO2 increase from 200 to 500 mg/kg but only a 7% increase when CO2 increases from
350 to 550 mg CO2/kg. Furthermore, the effects of CO2 enrichment change with age. Yield
increases of 16 to 19% are obtained in plants from March to June following fall and winter
CO2 enrichment of summer plantings. It is postulated that the limited yield increase due to
the fall and winter CO2 enrichment is because young carnations in the first year had limited
vegetative growth. Using CO2 enrichment from September to March, in turn, increase yield of
the second crop by increasing the number of lateral growths produced at the base of the
first crop flower stems.
Geraniums
The family Geraniaceae comprises five
main genera: Pelargonium, Erodium, Geranium,
Sarcocaulon, and Monsonia. The common geranium in most gardens belongs to the genera
Pelargonium. The zonal Pelargonium, also known as Pelargonium hortorum, is a hybrid
of Pelargonium species derived from wild types found in Africa and Asia.
Pelargoniums have extensive fibrous root systems that produce large number of small lateral
roots which in turn produce functional root hairs. Pelargoniums are also herbaceous plants
with shoots of limited secondary growth. The leaves are mostly opposite, simple, entire to
decompounded, stipulate, and the foliage is often scented. The flowers are irregularly
shaped with five petals. The two uppermost petals are usually larger and prominently
colored. The lower three petals are narrow and rarely quite small.
Geraniums grow best at day and night temperatures of 21 oC and 15 oC, respectively. Development
virtually stops below 9 oC while chlorosis occurs above 27 oC. Geraniums are strongly
responsive to light showing no growth at a light intensity of 10 umol/m2/s, some growth
but no bud development at 30 umol/m2/s, and flowering at light intensity above
76 umol/m2/s.
Carbon dioxide enrichment during plant growth and flowering appears to promote early
flowering and improved quality. A level of 2,000 mg CO2/kg applied to plants sown
in December increase fresh weight 4.3 fold while the same level applied to plants sown
in March increased fresh weight 1.4 fold.
Geraniums prefer low soil water tension levels for optimum growth. Geraniums grown at low
(40 kPa) soil water tension usually have greater shoot growth, and more advanced floral
development than plants grown at high soil water tension (100 kPa).
Geraniums are grown in several growing media. Rock-wool, for example, is used either alone
or as a component of growing media. A study of rock-wool based media amended with dolomitic
limestone, gypsum, phosphoric acid, potassium nitrate, and calcium nitrate show that media
containing 10, 20, and 30% rock-wool by volume produce plants of similar height, fresh weight,
shoot number, and quality rating than plants grown in commercial media such as Ball
Growing Mix II or MetroMix 350.
Petunia
The name Petunia is derived from Petun,
a name given to tobacco in Brazil. The genera
Petunia comprise about 30 species including Petunia axilaris and Petunia
parviflora.
Most petunia species are found in Argentina, Brazil, Bolivia, Paraguay, and Uruguay.
In the United States, petunia is an annual bedding plant.
Few studies are available on the temperature requirements of petunia. Petunia hybrida
produces the largest leaf area and the highest dry weight at root zone temperatures
of 21 to 35 oC and 13 h days. There is an interactive effect between day-length and
temperature. At 9 h days, maximum stem and inter-node length, greater node numbers,
and longer basal branches occur at 21 oC. At 16 h days, maximum stem and inter-node
length and greater node numbers occur at 26 oC. Flowering does not occur at 9 h but
at 16 h days, and it occurs 6 days earlier at 26 oC than at 21 oC.
Petunias strongly respond to day-length. Longer main stems are found in plants grown in
long days but more nodes and shorter inter-nodes in plants grown in short days. Plants
grown at 12 h days or longer are mainly single stemmed compared to plants grown under
short days (10 h or less). Flowering occurs earlier under long days and the total number
of flowers per plant is two times greater at 16 than at 12 h days.
Rock-wool is used as a growing media for petunias. Evidences indicate that plant height
and dry weight of petunias grown in 20% rock-wool media are equal or higher than plants
grown in commercial mixtures. The superior performance of rock-wool media appears to be
related to its lower water content and relatively high pH.
The water regime during growth strongly affects post-harvest quality of petunias. A study
on the effects of low, normal, and high irrigation frequencies during plant growth on the
post-harvest quality of petunias stored at 10 and 10 oC, 20 and 20 oC, and 30 and 30 oC day
and night temperatures have shown that at low temperatures irrigation frequency does not
affect quality. But as temperature increases, plants grown at high irrigation frequencies
decline in quality most rapidly. Plants grown under water stress, in turn, have slow flower
development and senescence, greater dry weight, and better overall visual quality than
plants grown at high irrigation regimes.
Nitrogen and Ca are essential for optimum growth of petunias but the requirements are not
well defined. Nitrogen applications to ensure a shoot tissue level of 4.4% are customarily
recommended. One study reports an application of 200 mg N/l determine a total N content
of 4.2% in shoots. Another study reports applications of nutrient solutions at varying
NO3 N/NH4 N ratios amounting to a total concentration of 15 meq/l, determine total N
contents in plant tissues of 5.1, 6.0, and 6.4% at1:0, 1:1, 0:1 ratios, respectively.
Rhododendrons
The genera Rhododendron (family Ericaceae) comprises a large group of evergreen or
deciduous shrubs. Most rhododendron cultivars grown in the United States are mainly
derived from crossing R. catawbiense with R. arboreum. Others are hybrids of
R. caucasicum
with R. smirnovi and R. griffthianum.
Rhododendrons are customarily propagated by stem cuttings. Stem propagation is influenced by
light, day-length, and CO2. Rhododendrons are found to be relatively insensitive to light
during rooting but rooting is stimulated by night break treatments particularly when low
light is used.
The effect of CO2 on plant growth is not well defined due to differential responses among
cultivars. Carbon dioxide enrichment during fall propagation has been found to inhibit
shoot development while spring enrichment reduced inter-node length but did affect shoot
production.
Rhododendrons are grown in media consisting of combinations of peanut hulls, pine bark,
and peat moss. Peanut hulls based media provides the best environment for plant growth
as peanut hulls apparently increase particle size, total porosity, and air space, and
decrease easily available water (water retained at 1 to 5 kPa), water buffer capacity
(water retained at 5 to 10 kPa), and bulk density.
Under natural sunlight rhododendrons require 2 to 3 years to produce plants with a crown
diameter of 25 to 40 cm. At present, there is a demand for smaller plants (one year or
younger plants). Studies indicate that manipulation of light appears to hasten flower
initiation. For example, floral initiation is earlier when light intensity increases
from 80 to 160 umol/m2/s. In turn, the number of floral primordia initiated increases
when day-length increases from 8 to 12 h at constant light of 160 umol/m2/s. Overall,
inflorescence development of rhododendrons increases with an increase in light intensity
and day-length.
Roses
Rosa (family Rosaceae) is the
Latin name of the genera Rose comprising about 200 species.
Roses in the United States are broadly grouped into 8 categories: (i) tea roses, (ii)
hybrid tea roses, (iii) polyantha roses, (iv) hybrid perpetual roses, (v) moss roses,
bourbon, and bengal roses, (vi) hardy climbing roses, (vii) shrub roses, and (viii) hybrid
rugosa roses.
Light affects rose flower production by (i) promoting sprouting of basal and lateral buds,
(ii) determining the photosynthetic rate and therefore flower production, and (iii) promoting
assimilate allocation in terminal buds for flower bud development. For roses, flower
production is potentially high during summer when light intensity is high and days are long.
The opposite is true in winter when light intensity is low and days are short.
The response of roses to light is cultivar specific and is modified by CO2. For Samantha
roses, for example, maximum photosynthetic rate occurs at lights of 450 to 500
umol/m2/s but maximum net photosynthesis occurs at 680 umol/m2/s and at CO2
level of 500 mg/kg.
Night temperatures of 14 to 16 oC with day temperatures 6 to 8 oC higher than night
temperatures are reported to be optimal for roses. Overall, mean daily air temperatures
of 20 to 24 oC are generally recommended. The maintenance of such temperatures can be
costly if greenhouse temperatures are above or below the range normally required for
plant growth. A practical way to reduce heating costs is by growing roses at suboptimal
temperatures (below the optimum). Some rose cultivars tolerate suboptimal temperatures
for a short period with no reduction in growth or yield.
Split night temperatures are another alternative to reduce heating costs. Roses grown at
alternate temperatures (18 and 12 oC) every 2 h produce 28% more flowers than roses grown
at a constant 18 oC.
An alternative strategy to split temperatures is the heating of the growing media. Media
heating requires less energy than air heating because of the high heat capacity of the media
and the smaller heat losses from greenhouses. Apparently heating the media up to 25 oC at
suboptimal day and night air temperatures of 16 and 11 oC enhances the breaking of dormancy
and growth of dormant buds. Maximum plant growth, shoot width, leaf number, breaks per
branch, and number and quality of flowers occur when the media is heated to 21 oC.
In greenhouse systems, roses are mostly grown in ground beds. In ground beds, higher
production and better quality of flowers are obtained from the cultivation of roses
grafted on an appropriate rootstock or rhizome than from cuttings. When rock-wool
and volcanic escoria are used as media the benefits of growing grafted from non-grafted
roses are virtually negligible.
The pH of the growing media is an important factor for roses. Roses grow well at pH around
5.7 but pH 4.0 causes inhibited root growth while pH 8.0 causes severe chlorosis, stunted
growth, and marked reduction in leaf size.
The quality of the irrigation water is another important factor for roses. A marked decrease
in the production of "Better Times" roses is reported when the EC of the irrigation water
increases from 1.0 to 1.5 dS/m. For "Forever Yours" roses, production is considerably
reduced when the EC of the water exceeds 1.8 dS/m.
Orchids
The word "orchid" derives from the Greek term orchis (testis), in reference to the testiculate
bulbs or tubers of orchids. The flower of an orchid has three sepals, three petals, one
of which is a modified petal or labellum, and a column. The column contains the
reproductive organs with male and female together in most orchids. The labellum
comes in a great variety of shapes and is probably the most dramatic feature of the flower.
Orchids (family Orchidacea) comprise over 750 genera and 20,000 species. All are herbaceous
plants, from the relatively large epiphytes of the tropical forests to the tiny plants
grown in temperate regions. Most tropical genera grow attached to trees (epiphytes) while
most temperate region genera grow in the ground, usually in forest humus or in bogs.
Orchids are generally grouped into terrestrial and epiphytal. The main terrestrial
tropical orchids are members of the Paphiopedilum which are tessellated leaved or
plain leaved. The epiphytes are either monopodial or sympodial. The monopodial are
mostly Vandas with either terete leaves or strap leaves. The sympodial orchids include
the Cattleyas (bi foliate or labiate) and the Cymbidiums (miniature and standard).
Cattleyas are the prettiest of all orchids and are the most popular species grown in
greenhouses. The flower is large, showy and well colored, usually purple in color but
because of widespread breeding, white, yellow, green, brown, and other colors are easily
found. Originally from the Andean slopes of South America, Cattleyas require temperatures
from 15 to 21 oC for optimum growth.
Dendrobiums grow from Japan and parts of China, throughout India, the Malaysian Peninsula
to New Guinea and northern Australia. There are basically three types of dendrobiums: (i)
horn or ceratobium, where the sepals and petals are twisted, narrow, and of equal size,
(ii) phalaenopsis, with large round flowers, and (iii) intermediate type, a hybrid of
the horn and the phalaenopsis types.
Dendrobiums grow as epiphytes in the tropical rainforests. Epiphytic Dendrobiums produce an
abundant and fine root system which holds them firmly in place on the tree branches and
at the same time traps debris in the form of death leaves and other plant residues which
rot down to provide a nutrient pool for plant growth. Dendrobiums are generally fast
growing plants, i.e. about 8 to 10 months to blooming. The flowers, which are generally
white or purple, can last for months in the plant. But when cut, they can last without
wilting for 3 or 4 weeks.
Cymbidiums require a large diurnal temperature (10 to 14 oC) differential to initiate
flower buds. High flower initiation occurs under day and night temperatures of 26 and
12 oC, respectively.
Overall, flower initiation of orchids is affected by N fertilization although the response
is not well defined. N fertilization apparently increases the vigor of vegetative renewal
shoots of Cymbidiums with no effect on floral bud development. On Cattleyas, increasing N
rates depress flower initiation.
In general the response of orchids to N fertilization lacks consistency. Some studies show
orchids growing successfully in inert media with periodic applications of nutrients while
others show orchids requiring little fertilization because of their slow growth.
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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