Group Title: CFREC-Apopka research report
Title: Heating the root zone of isolated 8-inch pots of Aglaonema during propagation and production - the water jacket technique
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 Material Information
Title: Heating the root zone of isolated 8-inch pots of Aglaonema during propagation and production - the water jacket technique
Series Title: CFREC-Apopka research report
Physical Description: 7 p. : ill. ; 28 cm.
Language: English
Creator: Henley, Richard W
Central Florida Research and Education Center--Apopka
Publisher: University of Florida, Central Florida Research and Education Center-Apopka
Place of Publication: Apopka FL
Publication Date: 1991
Subject: Plants -- Effect of temperature on -- Florida   ( lcsh )
Plant propagation   ( lcsh )
Aglaonema -- Effect of temperature on -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 5).
Statement of Responsibility: R.W. Henley.
General Note: Caption title.
 Record Information
Bibliographic ID: UF00065299
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 70054973

Full Text

[ I C ..,-'-
Heating the Root Zone of Isolated 8-inch Pots of Aglaonema During Propagation and
Production the Water Jacket Technique

R. W. Henley Marston Scnc

University of Florida, IFAS SEP 3 0 1994
Central Florida Research and Education Center Apopka
CFREC Apopka Research Report, RH-1.-20 F
university of Florida

During the past 10 years, many of Florida's foliage plant producers have adopted several
new technologies to produce higher quality plants more efficiently. One such technology is root
zone heating, frequently called bottom heating. This technology is employed during cool
periods, which for tropicals can be when the production environment temperature drops below
65 to 680F. Supplemental heat is provided under the plant to stimulate root development and
subsequent top growth with minimal use of energy. Most bottom heating systems are adjusted
to maintain a minimum temperature of 68 to 750F. Slightly higher temperatures may be
employed for special applications such as palm seed germination.

Many systems which heat a large amount of space around the plant before heating the
root zone tend to be more heat-energy-wasteful. Some of the oldest root zone heating systems
used for greenhouse pot plant production involved placement of a few relatively large caliper
(1 1/4 to 2-inch) steam or hot water heating lines under raised benches to warm the surface
supporting the potted plant material and the air around the plants. These systems are most
effective for pot plant production when the bench tops are either partially open to convection
currents of rising warm air or are excellent heat conductors. If a bench top does not fit one of
these categories, the under-bench heating system is likely to be relatively inefficient.

An alternative approach to root zone heating is to place the heat directly in the bench or
bed through the use of numerous small diameter distribution lines which carry warm or hot
water. Much of the root zone heating technology adopted by Florida nurserymen falls in the
latter category. Depending on the tubing or pipe diameter, heat transfer quality of the tube,
water temperature, container size and pot spacing to be used, the growing area is equipped with
a network of parallel heating lines ranging in diameter from 1/4 to 1/2 inch or slightly larger,
spaced 2 to 6 inches apart. These heating lines may be installed on the tops of raised benches
or on or near the surface of ground beds. In a few cases, depending upon bench design, the
heat distribution tubing may be attached directly under a bench top with good heat transfer
characteristics, an option which leaves the upper surface with fewer obstructions to container

ns work rather we]

situations which have evaded root zone heating technology as it is now applied. Large, widely
spaced potted plants, usually set at floor level, and hanging baskets, normally arranged i
elevated linear patterns are usually not equipped with root zone heating systems. An experiment
was conducted at the Central Florida Research and Education Center Apopka during the winte
of 1990 and 1991 to address the challenge of more efficiently heating the root zone of widel,
spaced pots or other containers isolated from conventional root zone heating systems.

Materials and Methods

Four 8-inch, white hanging baskets (REB Plastics, Inc.) were modified by drilling tw<
holes through the middle of the container side wall approximately 2 inches apart, one above the
other, and inserting a length of 1/4-inch EPDM tubing (Biotherm Engineering, Inc.) through thi
top hole, making two loops close to the side wall and drawing the lead end out through the
bottom hole. The tubing inside the container was held close to the side wall with several fine
thread ties which were looped around the EPDM tubing and through tiny holes drilled in the
container. The input and return tubing leads outside the containers were 30 inches long. The
modified containers served as water jackets to warm the root zone of experimental potted plant


tipped with water jackets. The controlling therm

irm water when the me

Irature dropped below 70U"

to supplemental heat in the root zone had been documented previously (1,2). Three unifonr
freshly harvested cuttings 45-55 centimeters long and each weighing 95 to 100 grams (frest
weight) were stuck January 15, 1991 in each of eight 8-inch baskets (without hangers). The
cuttings were positioned half way between the central axis and the sidewall of the container,
Four of the eight planted containers were nested in the pots equipped with coiled tubing and the
others were placed on the same bench without water jackets. The potting medium was a

~ -

grown m a relatively humid greenhouse shaded to provide 1000-1300 foot-candles an<
maintained at 65"F minimum air temperature at bench level. The cuttings were watered
manually only when the medium surface became slightly dry. No mist was used during

Three thermocouples were positioned midway down in the potting medium 1/4 inch fron
the sidewall, midway between the sidewall and the central axis and on the central axis, t<
monitor temperatures in the root zone. Two additional thermocouples were placed halfway
between the sidewall and the central axis 1/2 inch from the upper surface and 1/2 inch from th<
bottom of the container. The copper/constantan type thermocouples were connected to
multistation electronic thermometer which was switched manually between stations.

February 26th and 27th were selected to make root zone and greenhouse temperature
measurements because the temperature outdoors was expected to be cool. Measurements begai
8 a.m. on February 26th and continued on 4-hour intervals through 8 a.m. the following

February 27th). The measurements taken at 4:00 p.m. revealed that there was little variation
in temperature at the mid-level and bottom of the pots either treatment (Figure 2). It was
apparent that most of the heat in the two container systems was being acquired from radiant
energy from the sun because the container in the water jacket was not receiving supplemental
heat. The potting medium temperature near the upper surface in both treatments was cooler
during both measurement periods, primarily the result of water evaporation from the soil
surface. The strongest vertical gradient was observed at 4:00 a.m. in the heated containers
where the difference in root zone temperature from the middle of the pot to the top was 3
degrees while the difference in the non-heated pot was 1 degree. The temperature 1/2 inch
below the surface in non-heated pots was 64.0F at 4:00 a.m., while the ambient greenhouse
temperature ranged between 64 and 69F, as the forced air heating system cycled on and off.

The horizontal temperature gradients were greatest during periods when heat was supplied
to the water jacket equipped containers (Figure 2). Approximately 1/2 inch inside the side wall
the medium temperature fluctuated considerably as the warm water in the jacket cycled in
response to the controls. The mean temperature at 4:00 a.m. in the outside 1/2 inch, during a
10 to 15-minute period, was 94*F while the temperature near the center of the pot was 71.0*F,
a gradient of approximately 23 degrees in 3 1/2 inches. The mean temperature from the 5
sensors taken at 4:00 a.m. were 65F and 77F for the non-heated and heated pots, respectively.

Growth responses of Aglaonema 'Silver Queen' to the treatments, without bottom heat
and with the warm water jacket, are shown in Table 1. The values presented are means of
measurements taken from 12 plants in each treatment on April 17, 1991, 90 days after sticking
freshly harvested cuttings. The increase in number of new leaves was not significant at the time
of measurement, but this would change within a month or two, as there were more than five
times as many leaf bearing basal shoots developing on the bottom heated plants compared to
those without heat. The larger number of swollen basal buds on the non-bottom heated plants
indicate side shoots were forming, but at a rate slower than the bottom heated plants. The
difference in plant growth weight reflects the additional tissue (leaves, shoots and roots) that
developed under the two treatments. The growth responses of Aglaonema 'Silver Queen' to
bottom heating is consistent with other reports (1, 2).


This study has demonstrated that widely spaced 8-inch hanging baskets or other
containers can be supplied with root-zone heating using the water jacket technique described
herein. Because of the need for an additional container equipped with warm water heating coils
and, ideally, some insulation to minimize heat loss from the outside of the water jacket, it is
unlikely the water jacket technique of root zone heating will be adopted commercially due to the
high cost of the system. However, there may be some special applications of the water jacket
container heating system which would justify its cost.

Literature Cited

1. Bodnaruk, W.H., T.W. Mills and D.L. Ingram. 1981. Response of four foliage plants to
heated soil and reduced air temperatures. Proc. Fla. State Hort. Soc. 91:104-107.

2. Henley, R.W., Robert Mellen, Jr., William H. Bodnaruk, Jr. and Dewayne L. Ingram.
1982. Root-zone heating innovations in Florida. Combined Proc. International Plant
Propagators' Soc. 33:583-589.



50 L..

12:00 16:00 20:00 0:00 4:00




8 A.M., 2/26 8 A.M., 2/27/1991

Figure 1. Root-zone temperatures in non-heated and warm-water-jacket-heated 8-inch containers
in a greenhouse over a 24-hour period.

4:00 P.M., February 26, 1991 Outside temperature: 72" F
Greenhouse temperature: 78"F

Nonheated container Water jacket heated container
4 inches

780F I 80F

inches 81*F 80"F 80F F 82 2F 82F 82*F

S80F 820F

2 1/2 inches -
Mean value from 5 sensors: Mean value from 5 sensors:
80*F 81F
Tubes for warm water

4:00 A.M., February 27, 1991 Outside temperature: 48"F
Greenhouse temperature: 64-69 F

Nonheated container Water jacket heated container

640F 71'F

65"F 65"F 65"F 94*F 74"F 71*F
65F-- 75"F

Mean value from 5 sensors: Mean value from 5 sensors:
65*F 77 F
Tubes for warm water

Table 1. Growth of Aglaonema 'Silver Queen' leaves, side shoots, basal buds and plant weight
in non-heated and bottom heated containers.

Treatment No. leaves No. side No. swollen Growth of
shoots basal buds top (g)

container 3.5z 0.6 1.3 96

container 4.0 3.1 0.5 147

SValues are means computed from 12 measurements.

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