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AGRICULTURAL RESEARCH & EDUCATION CENTER
IFASO Univetrity of Florida
Bradeflton, Florida

EFFECTS OF LIGHT AND TEMPERATURE ON KEEPING QUALITY OF CUT FLOWERS
S. S. Woltz and W. E. Waters

Bradenton AREC Research Report GC1976-4 February, 1976

Research at the AREC-Bradenton Has indicated that lightingis a procedure that
may be used to maintain cut-flowers, especially chrysanthemun- i7eseful condition
longer than would be the case in darkness or very dim light. Information on the
response of cut-flowers to light should be helpful in understanding the post-
harvest performance especially if a grower receives varied reports-from customers
as to the keeping quality of his product. Most of the work to be 'described here
was conducted with chrysanthemums following an observation that cut pompons placed
in a well-lighted location (400 foot candles to full sunlight) lasted about four
times as long as flowers placed in a location where the incident light was only
20 foot candles.

The common attitude of consumers toward cut flowers is that they do not respond
to the light after harvest, or else, light is simply not considered as a factor
of importance. Our experiments indicate, however, that if the leaves of
chrysanthemums are green and not excessively wilted after harvest, they can carry
on photosynthesis to a significant degree in light of low intensity.

Photosynthesis is a very fundamental process, the basis for the existence of life
on this planet. Chlorophyll in the leaves of plants is the essential ingredient
that traps light energy from either sunlight or artificial light and converts the
light energy into the chemical energy of sugars and other organic compounds
manufactured from carbon dioxide and water. The speed of photosynthesis increases
with increasing light up to about 1200 foot candles striking the leaf surface.
Sunlight has an intensity of 10,000 foot candles or more. Red and blue light are
the most effective portions of the spectrum in the photosynthetic process.

The effect of temperature on the keeping quality of flowers after harvest is well
recognized and refrigeration is commonly used in the floral trade to prolong
their useful life. Temperature is very important because of its effect on
biological activities, particularly respiration, which is the process by which
living organisms oxidize sugars, starch and fat to release energy for vital
processes. In the process of plant respiration oxygen is consumed and carbon
dioxide evolved. The faster respiration goes, the faster the organic food reserves
of cut flowers are consumed. Respiration is dependent on temperature as a rate-
controlling factor. According to the Q1 rule of biology, for every 10C (180F)
temperature decrease, there is an approximate 50% reduction in the rate of food
consumption. For example, starting at 940F, a decrease to 760 results in a
reduction to one-half rate; lowering to 580 results in one-quarter rate. A
further reduction in temperature to 400 results in a rate of respiration one-
eighth of that at 940F. In addition to the effect on respiration, temperature
reduction slows most vital processes and slows the hands of the biological clock.

-2-

The first of three sets of experiments to be reviewed here was carried out in the
laboratory at room temperature. Bluechip chrysanthemum cut flowers were subjected
to light from white fluorescent tubes ranging from 0 to 400 foot candles. As
light was increased stepwise from 0 to 200 foot candles, there was a marked
increase in cut-flower longevity, improved quality maintenance, retention of
desirable foliage quality and retention of vital capacities of leaves in terms of
photosynthesis and respiration.

The second experiment was designed to study the interaction of fertilization
levels during production with subsequent storage of the Iceberg flowers at 400,
100, 25 and 0 foot candles. After only 4 days storage at room temperature
(750F) there was a stepwise decrease in chlorophyll content and photosynthetic
capacity going from 400 to 100 to 25 to 0 foot candles. Storing cut chrysanthemums
for seven days in the dark greatly lowered photosynthesis and chlorophyll levels.
3y 10 days, photosynthesis and chlorophyll were cut in half successively by each
reduction in light; tests for photosynthesis and chlorophyll were negative for
leaves from flowers held in total darkness. The photosynthetic efficiency of any
chlorophyll remaining after the passing of storage time decreased at room
temperature.

In the third experiment 'Iceberg' chrysanthemum stems from 12 nitrogen fertilization
programs were placed in distilled water under conditions of lighted and darkened
cold storage at 450 as well as light and dark at 750. The purpose of this
experiment was to learn whether chrysanthemums could manufacture important amounts
of food at cold storage temperature and permit one to take advantage of the
greatly reduced respiration rates. The very important factor of nitrogen
fertilization was included to learn the interactions with light and temperature.

To make a long story short, the chrysanthemum leaves, lighted from the bottom with
120 foot candles did carry on photosynthesis for long periods of time up to 42
days in storage. Table 1 shows the numbers of days flowers and leaves lasted.
In order to bring out differences that exist between treatments, the leaves or
flowers were observed until they had deteriorated to the point of being of no
value. Florists would, of course, discard them sooner but some home owners would
keep them to the bitter end.

Table 1. Average number of days of vase-life of chrysanthemums
under different storage conditions.

450F 750F
Dark Light Dark Light

Flowers 33 37 13 20
Leaves 28 37 8 26

There was a strong interaction between nitrogen fertilization and the response to
light. A comparison of light versus dark storage for high versus low nitrogen
revealed an interesting interaction. When tested in the light, high nitrogen was
superior; in the dark, low nitrogen was superior. To explain this, it should be
pointed out that high nitrogen leaves contain more chlorophyll and can photo-
synthesize more effectively than nitrogen deficient leaves; hence better results

in the light. Low nitrogen levels typically contain better carbohydrate (photo-
synthesis product residue) reserves and therefore have better vase-life under
dark storage conditions than leaves that have recently received large amounts of
nitrogen.

The question of beneficial effects of lighting for other cut-flowers has to be
approached on an individual basis. An exploratory experiment indicated little or
no benefit to glads, roses and asters. The photosynthetic and respirational
efficiencies of leaves of 5 types of flowers at 3 light intensities are shown in
Table 2 on the second chart:

Table 2. Respiration and photosynthesis of leaf disks
microliters of oxygen per gram per hour.

from cut flowers,

Photosynthesis
Respiration 400 ft C 800 ft C 1200 ft C
uL u.L u L t:L

Chrysanthemum 48 166 274 282
Rose 96 131 177 253
Gladiolus 58 52 86 131
Lily 41 66 90 115
Narcissus 53 82 112 140

To illustrate that leaves still can carry on photosynthesis after flowers are
cut the results of photosynthetic activity tests for leaves obtained from the
cold storage of a local florist are shown in Table 3.

Table 3. Photosynthesis at two temperatures expressed in microliters of
oxygen per hour per gram fresh weight of leaf disks.

420

u.L uL

Carnation 74 188
Chrysanthemum 88 588
Gladiolus 32 221
Rose 107 157
Snapdragon 54 306

-4-

In summary, light, either artificial or from the sun, will significantly prolong
the vase-life of chrysanthemums. The benefit is in proportion to the intensity
up to the point that light and heat cause excess wilting. A small amount of light
such as 7 foot candles is only of limited benefit while light in the range of
50 to 200 foot candles is quite beneficial. All experiments were run with
continuous lighting. It is not yet known whether a dark period would be helpful
although experience with other plants indicates a dark period would be of value
to permit the flowers to rehydrate. There could be some importance in a daily
rhythm of light and dark. Chrysanthemum leaves coming out of cold storage
usually respond to light. Also, if the leaves are green and do not remain wilted,
they probably will respond to light.

This information on light effects on cut flowers should be used in the education
of florists and consumers to hold cut-flowers under lighted conditions (natural
or artificial) as much as possible.