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Copyright 2005, Board of Trustees, University
For Commercial Use Only
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciencesy
UIni e r cE % of I l)ridi. Giine li eI
John T Wose Deain for Exten~ion I
'" _.^_--- ---_ ____ ._ '.."" ^ ^^^------ ~ f
INSTALLATION OF MIST PROPAGATION EQUIPMENT
David F. Hamilton and James T. Midcap*
When propagating plants by cuttings, it is important to pre-
vent wilting until roots are produced. Maintaining plants in a
turgid state requires a humid atmosphere accomplished by a
misting system. There are two types of mist application, con-
tinuous and intermittent.
Continuous misting systems are not recommended for com-
mercial operations. They lower the temperature of the rooting
medium, resulting in slow rooting, and cause excessive leaching
of nutrients from the foliage. In addition, too much water can
reduce oxygen in the rooting medium and create a favorable en-
vironment foi decay-causing organisms.
Intermittent mist (i.e. mist "on" for a specified period and
"off" for a specified period) reduces leaching of nutrients and
helps prevent excessive water in the medium. Intermittent mist
also negates some of the cooling effects found under continuous
mist systems. This system can be developed in various ways and
most control mechanisms are readily available.
Intermittent mist may be used in greenhouse benches or in
outside beds. Raised beds are preferred to ground beds. Ground
beds should be equipped with drainage tiles to insure adequate
drainage (Fig. 1).
Bed length whether raised or above ground can vary with
needs of the propagator. But bed width should not exceed 60
inches since this is the most efficient width to work from both
sides. Height of raised beds can vary from 30 to 36 inches, de-
pending upon type of construction.
There are two types of intermittent mist lines-overhead and
in-bench. In-bench mist lines, usually used in ground beds as
support for overhead mist, may not be feasible. With overhead
systems, the water supply line and nozzles are placed over the
center of the bench. These are easier to install and maintain than
in-bench systems since all parts are readily accessible.
With in-bench mist systems, the supply can be placed along the
bottom of the bench under the medium or directly on the surface
of the medium. Nozzles are placed on upright pipes attached to
the supply line.
Mist systems used outside must be protected to eliminate wind
drift and insure complete mist coverage. Otherwise, cuttings will
* Extension Rural Development Specialist and Extension Woody Ornamentals Specialist,
6"x 8" x 16" CONCRETE BLOCI
1/2" HARDWARE CLOTH,
Figure 1. A cutaway view of construction of a plant bed for outside conditions. Width
of bed should not exceed 60 inches. Nozzles are spaced 30 inches apart and
15 inches from sides and ends of bed. The first layer of concrete blocks facili-
become dry. Ten minutes without water on a hot, sunny day can
desiccate cuttings. In areas where freezing temperatures occur
during winter months, check valves should be installed on the
end of each line for drainage after each misting cycle.
All systems for intermittent mist require solenoid valves to
control flow of water through the system. Solenoid valves are
available in two designs: the normally-open type and the nor-
mally-closed type. The normally-open valve is constructed in such
a way that if electric power becomes disconnected, the valve
is open and allows water to pass through. Flow of electric cur-
rent closes the valve and shuts off the water. If an accidental
power failure occurs on the solenoid line or any failure in the
time clocks takes place, the mist remains on continuously with no
permanent damage to the cuttings (Fig. 2).
A normally-closed valve requires electric current to open and
allow the flow of water (Fig. 3). Power failure to the valve
causes the mist to stop. This could cause severe damage or loss
of cuttings due to desiccation.
The normally-closed solenoid valve is more readily available
and a cheaper initial investment than the normally-open valve.
It will operate as efficiently as the normally-open valve, but has
the disadvantage of remaining closed when electricity is off. To
eliminate this problem a bypass can be built into the system so
that when power fails the mist can be manually operated (Fig.
3). However, if water pumps also operate from electric current,
the bypass would also be inoperative in a power failure.
For safety purposes, the solenoid valve should be the type
which operates from 24-volt current. To reduce the normal
100-200 volts of current a 24 to 27 volt transformer should be
installed for wiring the valve. Because the solenoid is usually
close to water, this is an inexpensive safety item.
The most satisfactory mist nozzles must break water droplets
into very fine particles or fog so that droplets fill the area
around cuttings, wetting both sides of the leaves. The primary
function of mist is to produce 100 percent humidity and a con-
tinuous film of water over the entire leaf surface.
Two types of mist nozzles are available for plant propagation:
(1) the oil burner types and (2) deflection or baffle types. Oil
NORMALLY OPEN SOLENOID [ GATE VALVE
N\\W I I !I -I
Figure 2. Schematic diagram showing a mist system with a normally-open solenoid valve.
NORMALLY CLOSED SOLENOID VALVE
WATER MAIN BYPASS LINE
STRAINER C \--GATE VALVE
Figure 3. Schematic diagram showing a mist system with a normally-closed solenoid valve.
burner nozzles produce a very finely distributed spray bypassing
water through small grooves at angles to each other. This type
of nozzle uses very small volumes of water (2.5 to 5 gallons per
hour), but they require high water pressures (50 to 100 pounds
per square inch) to operate satisfactorily. In addition, high pres-
sure nozzles cover only 3 to 4 feet of area per nozzle, and several
nozzles are needed to achieve adequate coverage. Spacing from
30 to 48 inches apart will usually give sufficient coverage. Oil
burner nozzles are often more expensive initially than deflection
types and have a tendency to become clogged more readily.
Most commercial propagators in Florida use deflection type
nozzles. They produce a rather coarse spray from water striking
a flat surface. The larger aperture used in this type greatly re-
duces clogging but uses larger volumes of water (4 to 20 gallons
On the other hand, deflection nozzles will operate with water
pressures as low as 20 to 30 pounds per square inch and will
cover a greater area than high pressure types, usually 5 to 6
square feet. Therefore, a smaller number of these nozzles are re-
quired. Usually a spacing of 48 to 60 inches is satisfactory for a
Regardless of the type of nozzles used, they should be spaced
effectively to cover the propagating bed. Mist nozzles should pro-
duce a spray with an umbrella type pattern of 360 degrees. Dif-
ferent brands of nozzles deliver different mist patterns. There-
fore, individual nurseries must select the type that fits their
operation. Generally, a nozzle that delivers no more than 5 to 6
gallons of water per hour in an even dispersal of mist is desir-
able. It should be designed to operate as efficiently at 25 to 30
pounds pressure as it will at 100 pounds pressure.
Ideally, nozzles should be nonclogging and nondripping, easy
to clean, low in cost and easy to install and maintain. Nozzles
should fit standard plumbing fittings. Most nozzles can be ob-
tained with a plastic, stainless steel, or brass orifice. Those with
a stainless steel orifice usually cost twice as much as those with
brass, but they have a life expectancy five times greater than
the brass orifice. All types are available for installation directly
to the line with adjustable fittings or with steel and poly (PVC)
pipe or copper tubing.
INSTALLATION OF EQUIPMENT
There are some basic rules for installing a mist propagation
system that should be followed for a successful operation. First,
make sure the mist propagation line is installed completely level
or horizontal. This ensures that between misting cycles lines will
remain full of water so that when each cycle comes on, each noz-
zle will discharge water at the same time. A slight slope to one
end may be necessary for drainage on outdoor systems in areas
where freezing temperatures occur.
It is equally important that pipe from the solenoid valve to the
misting line runs upgrade and the solenoid is installed below the
level of the misting line. This is to insure that when the solenoid
valve shuts off, no water drains, forming air pockets from the
solenoid valve to the nozzles. Nozzles must be installed in an up-
right position with the spray heads facing upward (Fig. 4).
The height of the misting nozzles should not be less than 12
to 15 inches from the top of the propagating bed and not more
than 3 feet above it. If the bed is wider than 31/2 feet, a double
line should be installed over the bed.
Regardless of the type of nozzle used, it is impossible to spread
the mist more than 312 feet. Nozzles that spread mist greater
distances do so by increasing droplet size. Some growers prefer
larger droplet size in outdoor operations to minimize drift of the
mist from wind. However, if outdoor propagation areas are pro-
tected properly, the small droplet and finer mist are still more
desirable in terms of runoff and conservation of water.
For small installations, it is desirable to have a petcock in-
stalled on each line so that the system can be shut off at selected
sections. Usually in larger operations, an entire bed is filled with
cuttings at one time so that individual nozzle control is not
The purpose of the strainer is to filter water before it goes
through the solenoid, thereby preventing damage to the valves.
Strainers also help reduce clogging of mist nozzles. The most
commonly used strainer is the "Y" type with an 80-100 mesh
screen basket which can be cleaned. Other types of strainers such
as the "T" type or straight flow are equally effective.
Control of intermittent mist propagation systems can be con-
structed three ways.
1. A preset system without environmental overrides.
2. A preset system with environmental override.
3. A variable system dependent upon the environment.
All types have been used successfully by propagators, but the
variable system is the most sensitive and sophisticated.
110 VOLT OUTLET
Figure 4. Diagram of the overall mist system,
Preset Systems Without Environmental Overrides
Environmental conditions have no influence on misting fre-
quency when time clocks or humidistats are used for control.
Without environmental control, close personal observation is
needed and daily adjustment may be required.
The preset mist system requires two time clock controls (Fig.
5). The day-night or 24-hour timer turns the system on and off
at predetermined times. In addition, a cycle timer is wired to
the solenoid valve to regulate mist cycles when the timer is on.
The cycle timer is controlled by the 24-hour timer. Cycle timers
are available in several forms, including 1 minute maximum
cycle with 1 second on-off intervals, 6 minute maximum cycles
with 6 second on-off cycles and 12 minute maximum cycles with
12 second on-off cycles.
Humidistats have been used to replace the time clock systems.
However, as drying of leaves is not directly related to humidity
they are not the best means of control.
Preset Systems With Environmental Overrides
Some propagators use a thermostat-control system to override
the cycle of time clocks. When temperatures reach a certain level,
the thermostat overrides the time clock controls and applies con-
tinuous mist until the temperature is reduced. A sensing element
for the thermostat is placed just above the cuttings.
This system can also utilize a photocell to override the preset
time clock. A short period of mist is applied after a predeter-
mined amount of light has been received by the photocell. When
using light to override the time-clock system, the amount of
misting does not vary. Only the intervals between applications
will vary. Therefore, the higher the light intensity, the more
frequent the mist will turn on. This system is effective only in
plastic or greenhouses where high humidity can be maintained.
Variable Environmental Cycles
With variable systems there are no time clocks, but there are
separate systems related to light, evaporation, or weight that
control the cycle.
An electronic leaf system maintains a uniform level of hu-
midity at the leaf surface. Two electrodes are imbedded in a
plastic or noconductive surface and are wired to a control box
connected to a solenoid valve. The electronic leaf is activated as
water evaporates from the plastic surface and cuts off as water
covers the surface.
Figure 5. Schematic drawing of a proset cycle mist propagation control setup.
This system can vary with placement of the leaf in the propa-
gating bench, and it is difficult to use outdoors because the wind
influences the amount of water applied. In areas where water
has a high salt content, salts tend to accumulate on the plastic
and prevent the leaf from turning the water on and off properly.
The weight system is another type of environmental cycle con-
trol (Figs. 6 and 7). When enough water collects on a small
stainless steel screen, it is lowered, activating a mercury switch
which closes the solenoid and turns off the mist. As the water
evaporates from the screen, it rises and closes off the mercury
switch, which opens the solenoid valve and turns on the mist.
Where water has a high salt content or fertilizer injectors are
used, the screen must be cleaned periodically to prevent a buildup
of salt or the system could be held indefinitely in the on position.
Environmentally dependent light operated systems are avail-
able which operate without time clocks, or other controls. They
operate strictly on light accumulation in a photocell. After the
photocell has absorbed a predetermined amount of light in a
given period of time, the solenoid is activated. However, for this
system to be effective for outdoor use, adequate protection must
Probably the most frequently asked questions after a discus-
sion of mist propagation are: (1) What is the best system, (2)
how much water should be applied and (3) what cycles are best?
The system that is best for one propagator may not be best for
another. Cycles, such as 5 seconds of mist per each 10 minutes
or 2 seconds per minute, will have to be adjusted to the cultural
and environmental conditions at individual nurseries. Absolute
requirements dictate that the rooting medium remain moist but
not wet and that a film of water be constantly present over the
cutting surface. The system used must be regulated to obtain
these conditions. Cuttings must be misted until well rooted. How-
ever, misting frequency should be reduced as cuttings begin to
root in order to avoid soft and weak growth.
COSTS FOR INTERMITTENT MIST PROPAGATION FACILITIES
While much has been written about the principles, techniques,
and equipment required in intermittent mist propagation, little
information is available concerning basic prices associated with
obtaining this equipment.
Cost of mist controlling devices, nozzles and other equipment
will vary considerably, depending on type, source and quality of
equipment selected and the particular requirement of each pro-
MENT IN PROPA-
Figure 6. Schematic drawing of a mist propagation system where mist Is controlled by a
sensing element from which water evaporates.
Figure 7. Schematic diagram of Mist-A-Matic system for propagation.
(Photo courtesy of E. C. Geiger Co., Harleysville, Pa.)
pagator. There will be cases where booster pumps may be re-
quired to increase line pressure, or special filters may be neces-
sary if the water supply has a large amount of particulate
matter. Special equipment of this type obviously would increase
the basic cost of installing the mist propagation system.
Cost figures for an intermittent mist system, regulated by a
24-hour time clock with an interval timer are presented in Table
1. These figures are for an existing raised bed where the water
source is readily available. Costs of the bench construction or
actual installation of the intermittent mist system will not be
Nozzle types and the mist control system used in determining
the cost of equipment were selected because of their popularity
and common usage in the trade. The actual prices of all material
Table 1. Supplies and equipment necessary to install an intermittent
existing raised propagation bench 4 ft. x 50 ft.
mist system in an
Quantity Description Cost*
50 ft. 1/2 inch PVC Pipe at $2.99 per 100 feet. $ 1.50
17 Flora-Mist Fogger Nozzels at $.70 11.90
2 1/2 inch PVC T's at $.38 .76
2 1/2 inch PVC 900 ELLS at $.34 .68
1 1/2 inch PVC Cap at $.25 .25
17 '/2 inch PVC Pipe Saddles at $.26 4.42
1 1/2 inch Solenoid Valve at $36.00 36.60
1 24 Volt Transformer at $8.00 8.00
1 1/2 inch Globe Valve at $4.00 4.00
4 /2 inch PVC TXS Male Adapters at $.28 1.12
1 '/2 inch Line Strainer at $13.82 13.82
EQUIPMENT SUBTOTAL 83.05
1 24-Hour Time Clock 20.30
1 Interval Timer-6 minute cycle with 6 second
adjustable increments 34.85
TOTAL WITH TIME CLOCK SYSTEM $138.20
1 Mist-A-Matic Control System 116.00
TOTAL WITH MIST-A-MATIC $199.05
1 MacPenny Electronic Leaf 105.00
TOTAL WITH MACPENNY ELECTRONIC LEAF $188.05
1 Solatron Model 561-9 150.00
TOTAL IN SOLATRON SYSTEM $233.05
*Prices from 1976 Distributor Price Lists.
listed in Table 1 were derived from 1976 dealer price lists in the
catalogs of nursery and greenhouse suppliers.
The Flora-Mist nozzles were selected for discussion because
of their common usage in the trade. Cost of other comparable
nozzles are listed in Table 2. The Flora-Mist nozzles are designed
with a standard 1/8 inch pipe thread and can be inserted into a
/2-inch PVC pipe when a saddle is used. The pipe saddle is
cemented to a l/2-inch PVC pipe where a nozzle is desired. Using
a 5/16-inch drill, a hole is drilled in the 12-inch PVC pipe fol-
lowing the attachment of the pipe saddle to the feeder line, and
the Flora-Mist nozzle is then inserted into the pipe saddle.
Operation of other regulatory systems such as the electronic
leaf, Solatron and Mist-A-Matic have been discussed. Cost figures
for these three systems are listed at 1976 dealer prices in Table
1. While these systems will increase the cost of the intermittent
mist bed, it must be noted that they are much more sensitive
systems and ultimately give better control of mist and water
level in the propagation bed.
Table 2. Characteristics and cost of some commonly used nozzles for intermittent mist systems.
Area of Operating Rate of
Coverage pressure discharge
Description Type (dia. ft.) (Ibs./sq. in.) (gal./hr.) Cost Comments
Mister Green Fogger
Fog-Mist Nozzle #550
Fog-Mist Nozzle #551
Supreme Electric A6
Supreme Electric T16
$ .60 1/32 inch orifice
1/8 inch std. pipe threads
.040 inch orifice
1.10 5/16-24 machine threads
3/ inch std. pipe threads
'1/ inch std. pipe threads
5/16-24 machine threads
1/2 inch pipe fitting
When the electronic leaf system is used, the 24-hour time clock
and interval timer are excluded. However, the total cost of the
propagation system increases to $188.05, based on the 200 square
foot model. With the Mist-A-Matic system, the 24-hour time
clock and interval timer are again excluded, but the total cost
increases to $199.05 in the same model. Likewise, the Solatron
system operates without either of the time clocks, but its use
increases total cost of the system to $233.05.
The use of trade names of products, equipment, firms and costs of
products is solely for the purpose of providing specific information.
It is not a guarantee or warranty of the products named and com-
pared and no endorsement is intended nor criticism implied of similar
but unnamed products.
This publication was promulgated at a cost of $299.06, or
6 cents per copy, to provide information to nurserymen and
their employees on mist propagation of woody ornamentals.
Single copies are free to residents of Florida and may be obtained
from the County Extension Office. Bulk rates are available upon
request. Please submit details of the request to C.M. Hinton, Publi-
cation Distribution Center, IFAS Building 664, University of
Florida, Gainesville, Florida 32611.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 19141
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
K. R. Tefertiller, Director
Institute of Foond d Agricutural Scienc
University of Flor^^id