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Vegetative Propagation with Fogging -
compared with traditional Methods

The Traditional Method :

Cuttings taken from strong and healthy mother-plants are planted into growing-beds, multi-plates or containers, watered freely and placed in a propagation-house (glasshouse, foil-tunnel, etc). If necessary the cuttings are treated with rooting-hormones, the propagation-house however, provides no special climate.

Cutting off means a radical withdrawal of all necessary as nutrients and therefore is a veritable shock for the cutting. During the following 2 - 5 days a "Wilting Phase" dominates which can be overcome only with difficulties and usually takes a heavy toll on the cuttings. All surviving cuttings are weakened considerably for the next period of time and will start slowly with root production.

The Alternative :

At this point the considerable advantages of propagating cuttings under foggy climate become clear. The planted and moderately watered cuttings are placed into a special propagation-house with moisture-saturated air ( 100% relative humidity ). This climate provides the ideal surroundings for the "shocked" plantlets, prevents the "Wilting Phase" and the subsequent weakening - the cuttings can immediately begin with root production.

Fast and abundant production of new roots depends on many different parameters. Without referring to special demands of various types of propagated plants we will mention some of the most important parameters :

  • Composition of Substrate ( for instance add-ons like Perlit, Peat, Sand, Gravel, etc )
  • Ground-Humidity resp. Ground-Temperature
  • Air- Humidity and Air-Temperature ( specially the micro-climate inside the leaf-area of the cuttings ! )
  • Light-Intensity or necessity of Shading
  • Leaf-Temperatures
  • Fertilization resp. Application of Add-Ons (Fungicides, Disinfectants, etc )
  • etc, etc...

An undisputed fact is that root formation is made much easier if the substrate stays well aerated and evenly humid. If the micro-climate in the leaf-area is correct the rooting-time can be shortened considerably by an aerated and humid substrate.

With conventional watering systems ( hand watering, sprinkling system, ...) rooting can be retarded because the rather large droplets provided by these systems tend to overwater some areas and to compactify the substrate, thereby lowering aeration.

If the periods between waterings are lengthened to minimize overwatering the cuttings however tend to dry off, so that the ideal humidity cannot be maintained until the next watering.

The ideal method to provide the needed macro- and micro-climate for cuttings is therefore water distribution by High-Pressure Fogging which is the only technology taking all parameters into consideration.

Provided the fogging system has been parameterized correctly it creates in a very short time a dense, hovering fog which will descend gently into the propagation area and will - most important - also penetrate into the leaf-area of the cuttings, creating the above mentioned micro-climate.

The leaves breathe by means of their stomata on the underside of the leaves - providing this area with moisture guarantees that the plantlets get always ideal growth parameters. By means of the same process the substrate can be kept evenly moist (the fog in the airspace above prevents drying off) without getting overwatered. Root formation therefore will not be impeded.

To complete this short synopsis we want to remark that substrates for optimal propagation with fogging should be poor in hygroscopic substances like peat or standard soil. The composition of the substrate depends on the experiences and techniques of the propagating nurseryman with his cultures - some large propagation shops use substrates without any organic soil.

As examples we want to mention only

  • Rooting of Carnations in pure Perlite (Agrofrigor, Dunajska Streda) and
  • vegetative propagation of spruce in rough gravel (Mayr-Melnhof, Frohnleiten, Austria)

Conventional propagation usually needs shading - either inside or outside of the propagation house do prevent any burning during the periodic drying times between the waterings. Shading reduces the light (energy) input to the plantlets - lengthening the rooting period. With a correctly parameterized and installed fogging system the additional benefit of light reflection by the fog can be realized without reducing the intensity too much. Propagation nurseries in Cyprus use only a light coat of whitewash on their glasshouses during the periods of highest light intensity.

In this context we want to mention also temperature distribution in propagation-houses with fogging systems ( refer also to Theoretical Background : Air Movement in a Humidified Space). All water inserted into the house in the form of microscopic droplets will rapidly cool the air, mainly by means of the so called "Evaporation Cooling" and not by means of the enthalpy of the inserted water. The air cooled by this effect will fall down, forcing the remaining warm air upwards. In a propagation-house with a fogging system the coolest layer is above ground - where the rather small cuttings are placed - and within the leaf-area of the plantlets. This temperature-difference will create within a short time an "air-roller" which provides not only cooling but also air circulation.

An important setting, especially during the warm season (May, June), for the fogging system is to work with short fogging-periods to provide an even reflection of light and to activate the air-roller regularly.

During the intervals between fogging another temperature-regulating effect takes place. Due to evaporation of water from the slightly moistened leaves additional cooling will occur. Research into this effect at the Institute for Plant Physiology, University of Vienna, Prof. Dr. Bolhar-Nordenkampp, has shown that leaf-temperatures can be as much as 10C lower than the surrounding air-temperature !

Summing up we see that short period fogging can be used very successfully to lower temperatures in propagation-houses provided the cycle of foggings and intervals is kept quite short. Interval times should be set to prevent substrate heating by means of light intake.

Optimal propagation supported with fogging cannot be achieved by periodic fogging and control by means of a humidistat alone.
Most propagation beds have to be kept rather dry during dark hours to prevent fungus growth. As most propagation takes place during late Spring till early Summer, when warm nights help dry off the substrate, a more intensive watering must take place in the morning to start the daily growth cycle.

Plantfog-installation take care of this option and provide functions for the nurseryman to "water" his propagation-beds additionally (additional explanations can be found in Theoretical Background : Dewpoint )

Our control-panel for propagation houses (since 1986) contains a standard-option which allows startup in the morning with fog application for a preset time while disabling the humidistat during this "watering-period". If the fogging continues over the saturation point of the airspace the atmosphere cannot take up more water vapour, The water will condensate on the plantlets and the substrate. The nurseryman can decide how much water will be brought in by this function. Following the completion of this watering-cycle the fogging-plant resumes its normal operation of cyclic fogging. Plantfog thereby provides an almost fully automatic propagation program which will need only regular control and readjustment of parameters according to rooting progress.

One of the main advantages of fog-supported propagation is droplet-size.

High-quality fogging nozzles are using a feeding pressure of 50 - 70 bar and provide hovering water particles with a diameter of 10 - 25 micron (80 % of particles). The fog will also contain particles as small as 10 micron and a small part with diameters up to 50 micron.

The main parameter for fast and efficient evaporation of inserted water is the active surface of droplets, which will increase with the square power with decreasing droplet-diameter. Therefore the evaporation speed is much higher for micro-fog than for drops dispensed by any sprinkling apparatus.

During planning of fogging installations it is of utmost importance to take into account which plants are to be propagated and which area is to be treated with fogging. Derived from our long experience with propagation-houses we recommend that total saturation should be reached within 20 - 30 seconds. Only with this basic setting an even humidification can be provided over the propagation area without reaching the danger of local overwatering.

Control by means of Humidistats

To conclude some remarks on Humidistats. Everybody familiar with this topic will acknowledge that measuring humidity is one of the most difficult tasks. Humidity-sensors which will work correctly in ranges above 80 % relH and available at an affordable price still remain a dream. Moderately priced sensors on the other hand show such a large hysteresis that it is virtually impossible to use them for such a sensitive topic as rooting cuttings for propagation.

Plantfog-Systems take this into account by using the sensors only to prevent over-watering. The needed even humidification is provided by means of the settings of fogging- and interval-times.

Evaluation of alternative Technologies:

  • Spraying-Systems ( for instance Tegtmeier-, Gardena- or similar nozzle-designs ) cannot provide optimal water insertion as these systems show circular spray-areas. These circles must be placed with overlaps to cover the propagation area which will unfortunately create zones where the above mentioned problems of over-watering will occur.
  • If "downsized" fogging systems are installed [ fewer nozzles, therefore smaller pumps, smaller performance = smaller investment ] the customer will pay the prize in the long range as the propagation results will be not as good as expected.
  • A very drastic example of these effects has been observed during the development of the propagation areas for spruce (1988) for the nurseries of the Mayr-Melnhof forestry. Due to a nozzle arrangement with too few nozzles the rooted cuttings showed a wavy up and down growth pattern.
  • The technology of fog-supported propagation currently used with tremendous success all over Europe stems from the basic research performed by Plantfog in conjunction with renowned nurseries here in Austria.

Synopsis:

Ideal propagation context can be achieved if

  • the shortest possible timeframe can be reached for rooting and hardening of cuttings
  • propagation can be performed during the season(s) with optimal light and day- and night-temperatures
  • drop-out quota during rooting is kept at a minimum
  • additional costs for energy and additional labour during propagation remains negligible due to system performance and automatization
  • resulting quality of plants is raised above prize level reached with former methods
  • break-even time is extremely short compared with lifetime of installed system

Plantfog bases its propagation technology on 19 years of experience with renowned propagation nurseries

Fogging Nozzles, Systems and Controls have been developed in constant cooperation with renowned propagation nurseries and are subject to constant review and re-engineering

To sum up our experiences from Austria and abroad we can cite the benefits of fog-supported cutting-propagation compared with conventional methods and prove our numbers on request:

  • Reduction of rooting times up to 60 %
  • Reduction of dropout to under 3%
  • Breakeven (independent of installation costs !) reached within a maximum of three propagation seasons
  • Lifetime of our systems 15 - 20 years

 

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last modified MAR 2013
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