Logo for the Journal American Rhododendron Society

Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com


Volume 24, Number 2
April 1970

DLA Ejournal Home | QBARS Home | Table of Contents for this issue | Search JARS and other ejournals

Try This Balanced Closed Case Propagator
John G. Lofthouse, Vancouver, B.C.
Chairman, Propagation Committee

        The balanced closed cased propagation unit herein described, was presented to the Seattle, Tacoma, Olympia, Shelton and Portland Chapters, by the author in a series of lectures during October 1969. Much interest was shown, and requests made, that details be published in the journal at an early date.
        The unit is designed to quickly root Rhodos and Azaleas, even the more difficult varieties. They will develop large root systems, the basis of a strong and healthy plant. It is also recommended for germinating seeds and growing on. Plants will grow quicker, and bloom earlier.
Rooting Factors: The four environmental factors that influence the rooting ability of a cutting, are light, heat, moisture and air.
Light. This is the only source of new energy (provided by photosynthesis) for the accelerated cell growth in the cambium area, while the cutting is attempting to form new roots.
Heat. Proper temperature in the stem and leaf area is essential for satisfactory rooting. I have found, the optimum temperature is approximately 75 in the rooting zone, with 10-15 less around the leaves. As temperature of compost falls, rooting is slower, and cell action will cease at low temperatures.
Moisture. It is essential, that when a scion (cutting) is placed in a propagating bed, that humid air surrounds the leaves, and adequate moisture (but not too much) be available in the compost. Otherwise, loss of moisture through transpiration, will cause wilting and desiccation of the leaves and plant tissues.
Air. It is essential that clean fresh air be available to the leaves and rooting area. Fresh circulating air helps keep the leaves and stems healthy and free from bacterial and fungus infections. It also greatly accelerates the formation of roots.
        Closed case propagation units, in general use, fall short in two of these factors. Namely, sufficient light, and proper reaction. As most of this propagation takes place in the shorted days of Fall and Winter, and as these units still have to be out of the rays of the sun, optimum light for best rooting is not obtained. Also, as the top of the case is closed with plastic covers, or glass sashes, stale air is the result in the leaf zone, and worse conditions prevail in the rooting area. This results in leaf fall, and black decaying stems on some cuttings, particularly the more difficult to root varieties.
The Balanced Closed Case. With the foregoing factors in mind, the following unit was designed. Heat is provided in the conventional way, a soil cable with thermostat set at 75. High humidity is maintained by the evaporation of moisture from the compost. This is accelerated by the 75 temperature in the rooting medium, and retained by three pieces of overlapping polyethylene placed over the top. This was done for ease of handling, and so that each section could be attended to separately. (See picture of the completed unit.) Constant light is provided by two 40 watt industrial type fluorescent fixture, on for 16 hours per day, and suspended 12 to 16 inches over the unit. Use one daylight, and one deluxe warm white tube.
        The method used to provide aeration, makes this unit different from conventional closed case propagators. A specially prepared, open compost, is placed on a strong inch screen, which is open to air circulation from below. Four 1 by 12 inch ventilation slots are made on each side of unit near top (see photos). Air enters at bottom, below screen, goes through compost and out of ports at top, keeping stem and leaf area well aerated. Despite this, humidity reads 100% in area above the cuttings.

Balanced Closed Case Propagation Unit Balanced Closed Case Propagation Unit
   Fig. 25.  Balanced Closed Case
   Propagation  unit being fiber glassed.
    Fig. 26.  Balanced Closed Case
    Propagation Unit completed.
    Center polyethylene cover folded
    back. Note ventilation slots on
    sides and ends.
General Construction. I cannot go into details, but measurements and general construction of unit shown is as follows:
Material. ⅝ or inch waterproof plywood.
Inside Measurements. Length 6 feet width 2 feet height 14 inches. There are 6 (1 inch by 2 inch) cross members holding the screen. One on each end, and four others. A piece of 1 inch by 2 inch is attached to the bottom of the unit going from right front to left back. This provides rigidity. To provide durability, the unit was fiber glassed inside and sprayed with aluminum lacquer for greater light reflection and insulation. Fiber glassing is not really necessary, but a good synthetic or similar waterproofing lacquer should be used. (Watch for finishes that are toxic for plant growth.)
Compost Used. For the rooting medium I use Styrofoam mixed with peat. Styrofoam is light and extremely porous, does not absorb moisture, but is compatible with it. In early experiments, sand was used but was later discarded. Pathogens and fungi can be introduced with it, causing decay of the stems in certain varieties. The elimination of sand improves the drainage. Never again will you find the base of the cutting soggy and wet.  Proportions - 50% fine Styrofoam sifted through a " screen); 50% fine peat (pre-dampened).
        Before placing compost and cable, first put down a 1 inch layer of Styrofoam on screen. Above this place a 1 inch layer of compost. On this place the cable as per manufacturers' instructions. I use a 48 foot cable with the thermostat set at 75. I then lay another 3 inches of compost above cable. I recommend rooting in 3 inch bottomless plant bands. Cuttings can be removed without disturbing their roots. Also they can be removed without disturbing others that may not yet be properly rooted. If this procedure is followed, place bands in case and fill quite firmly with compost. After wounding and treating cuttings as described below, they can be inserted and watered well with a fine spray. If bands are not used, another 3 to 4 inches of compost should be laid down.
Wounding and Treating with Hormones. My way of wounding, and application of hormone to cuttings is different from the usual, and is described below. Normal cutting material approximately 3 inches in length is used. A wound is made 1 inches long on each side, cutting into the wood slightly, but terminating inch above the base. Full strength Jiffy Grow is applied by brush to the bottom inch of one side only (but not on base). Difficult to root varieties can receive this treatment on both sides with improved results. I have a specially made rack that holds these treated scions upright by their leaves. They are left there 5 minutes. Capillary action draws some of the hormone up the wound, weakening as it goes up the stem. Therefore, an optimum point is reached for ideal hormone concentration and ideal rooting conditions. The untreated side is a safety valve if the strength is still too strong. This method works for me, and damage is extremely rare.
Location of Balanced Propagator. The unit should be placed in an area where the temperature does not generally average over 60. At higher temperatures, leaf and compost areas cannot be maintained at the 10 to 15 differential as described in the early part of this article. Suggested locations are under greenhouse bench, unheated garages or basements where the temperature averages 40 to 60. Water cuttings as needed, possibly every 7 to 14 days. As drainage is excellent, over watering is not a problem.
Expected Results. By following the above instructions carefully, the Balanced Plant Propagator will give excellent results. To give an example of speed: Scarlet Wonder was rooting in 20 days. Reputed difficult to root hybrids such as 'Susan', 'Mrs. Horace Fogg', 'Britannia', 'Naomi' group, 'Crest,' and many others, have been rooted with comparative ease. It is ideal for germinating seeds, and growing them on to good sized plants. Use the same compost, but fertilize as roots develop. Dusting seeds with Rootone is a good damp off preventive with any germinating method. This Balanced Propagator is excellent for propagating other plants with similar environmental requirements.
        One word of caution. Do not allow plastic to cover ventilation ports. Also, raise unit on blocks if necessary to allow a free flow of air to enter under screen. If seedling plants are to be grown in this unit for an extended period, additional light may be necessary to prevent legginess. Although, proper pinching of buds will help to compensate for this.

Good luck.


Volume 24, Number 2
April 1970

DLA Ejournal Home | QBARS Home | Table of Contents for this issue | Search JARS and other ejournals