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Journal American Rhododendron Society

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


Volume 32, Number 4
Fall 1978

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Rhodies Under the Lights
by Max L. Resnick, Canton, Mass.
Reprinted from the Rosebay, Massachusetts Chapter

        For those of you to whom the winter months represent a void in your rhodie gardening, I offer the perfect solution. Grow them under lights and extend your growing season to 12 months! At a very moderate cost - requiring only a minimum of space and the only tools necessary a screwdriver, pair of pliers and small drill it is simple to erect an excellent fluorescent light set up. From seed to 4 to 6 inches in 6 - 7 months cuttings rooted in as little as 4 weeks, 2 or more flushes of growth by early summer - not only possible - but very common.
        My first experience with lights utilized an old 10 gallon fish tank. Such a tank measures 12 x 12 x 24 inches long. A standard 2 lamp, 20 watt fluorescent fixture also measures 24 inches and will fit exactly on the top of the tank. If one is a bit careful no securing is necessary. The reflector resting on the fixture completed the set up.
        I recall it was January. I took in a half-dozen plants in 4 inch pots from the pit - let them thaw out a few days in the garage, and put them under the lights to see what would happen. To me it was remarkable! Literally the plants overnight broke dormancy and new growth was soon evident. One plant of 'P. J. M.' had actually grown enough to touch the lights.
        However - such a light set up is not really satisfactory. First, it cannot accommodate a 40 watt fluorescent fixture more about which later, and then no rhodie enthusiast in his right mind is going to be satisfied with 6 or 8 plants.
        The light set up that I find most satisfactory utilizes open industrial shelving with matching end posts and 40 watt fluorescent lamps (almost a must). The shelves are 24 x 48 inches long and will accommodate these lamps which are also 48 inches in length. The end posts come in varying heights and are pre-punched at set intervals so that the shelves can be attached at any desired level.

Indoor Light Set Up Using Industrial Shelving
Indoor Light Set Up Using Industrial Shelving

  

Rooted cuttings of R. 'Goldfort'
Rooted cuttings of R. 'Goldfort'
Struck October, photo following January

       CONSTRUCTION: A unit with 3 tiers of lights will provide 24 square feet of growing space - enough for 120 4inch pots. Such a unit will require 4 shelves and three sets of lights as described. Steps in its construction are as follows:
1. Line up the top of each light fixture frame to the underside of each of three shelves, drill holes through both, and attach each light to the undersurface of each shelf by means of small stove bolts. The electrical cord must exit from the side of the fixture.
2. The fourth shelf (with no light) is bolted through the bottom hole of each of the 4 end posts, to become the floor of the unit.
3. The remaining three shelves (with lights attached to undersurfaces) are similarly attached at varying desired levels. For example, if the end posts are 69
inches in height, the shelves may be spaced equidistant, so that there are provided 3 shelves about 23 inches high. Or one may place one shelf higher than the other.
4. Crossbar bracers are then attached to the end posts on three sides by small bolts, diagonally from top to bottom. The bracers are merely narrow strips of metal that serve to brace the set up and prevent it from swaying.
5. The construction is completed by wrapping 4 mil plastic, clear or white, around 3 sides, leaving only the front unenclosed. This is secured by garbage bag type ties pushed through the plastic and end post holes. The plastic is helpful in the housekeeping, aids in maintaining humidity (more about which later) and reflects light.
        I would recommend a few other accessory items, inexpensive yet very helpful: an automatic timer to control the lights, a thermometer, hygrometer to read temperature and humidity, and a small portable humidifier. The latter may be of the table top type and need only have a 1 to 1½ gallon capacity.
That plants do so well under the lights should really not surprise. Under the lights one can approach and control ideal conditions as concern light, temperature, and humidity. To put it another way - give the plants what they like and they will respond! Further discussion of the above may be helpful.
        LIGHT: The amount of light that the plants receive varies directly with (1) the number and intensity of the fluorescent lamps, (2) the length of time the lamps are on, and (3) the distance of the plants from the lights.
        Standard size lamps are either 20 watt (24 inches long) or 40 watt (48 inches long). It is recommended that only these be used. Best results will be obtained with the use of 40 watt lamps. Somehow, here is a case where 2-20's do not equal 40. I have one light set up that uses 4 20-watt lamps and another set up that has 2 40-watt lamps. Although the total wattage is the same in each, empirical observation of the growth shows a distinct difference, favoring the latter. Thus the importance of a set up of sufficient size to accommodate 48 inch lamps.
        Fluorescent lamps are generally lights of two types. These are the common white light and colored light, the so-called plant grow lights. A detailed explanation of the properties of light is beyond the scope of this article. Suffice to say that white light breaks down into a spectrum of colors, the more important of which for plant growth are the reds and blues. It is in these colors that the grow lights are strong. Several brands are on the market, all probably of equal merit. I happen to use Sylvania's "GRO-LUX WIDE SPECTRUM (WS)", reputedly especially strong in the reds and incidentally the least expensive. One other point: the grow lights should be used in conjunction with the white lights. If your fixture has two lamps, use one white light and one colored; if it has four lamps, alternate two white with two colored.
        How long do you keep the lights on? It is generally accepted that 16 hours per day is optimum. Empirically, I can say that my plants do well with that amount. It is essential that the lamps be turned on and off at the same times each day, so that the days and nights for the plants come at the same time - thus the importance of an automatic timer.
        Actually, I have found that the distance of the plant to the light (as far as rhodies are concerned) is not that critical. Obviously, you would not put a germinating seedling 23 inches away, nor a tall plant so that it hits the light. A rule of thumb is the smaller the plant the closer to the light. Not enough light is manifested by straggliness; too much, by leaf burn. A simple method of raising a plant closer to the light is to place its pot on another pot, inverted. But really you will find that this is not a problem to be concerned with.
        TEMPERATURE AND HUMIDITY:  Ideally, daytime temperatures should approach 70-75 degrees F, with a 10 degree drop at night. The latter is of great importance. Under usual household conditions temperature should pose no great problem - improvisation at times. The shutting off of the lights at night will in itself help get the nighttime drop.
        Contrasted with the above, a bigger problem can be presented by humidity, or rather lack of humidity. It tends to dry out indoors, especially in the winter time with the heat on. Your plants will not do well under dry conditions. The enclosing plastic will help retain moisture, as will the plants themselves close together. I have two other suggestions. Do not rest the pots directly on the shelves, but in horticultural trays that have been almost filled with gravel or perlite. By keeping the latter wet a great deal of moisture will be retained. Also, use a humidifier. I use a small portable 1½ gallon size humidifier (cost under $15). When the heat is on, I run it during the day-time hours. It is necessary to refill the water only every other day. Under these conditions, I can easily maintain a relative humidity of 50-60% or more - which is just fine for the plants.
        What does well under the lights? Just about anything. One can grow a veritable forest - limited only by space and interest. Azaleas do equally as well. For those of you who have mastered the art of rooting deciduous azaleas, the problem of getting that first flush of growth is no more. Interested in rooting cuttings? Make your propagating flat just under 48 inches in length and it will fit perfectly into the shelf. Place it on any but the bottom shelf and you will have "bottom heat" from the underlying fixture. You can expect at least 2 flushes of growth by the following June.
        SEEDLINGS: My own interests lean more and more to germinating and , growing on plants from seed. The excitement of creating something new - perhaps an ultimate "winner" - is something I cannot resist. I suspect that sooner or later many of you will be bitten by this same bug. Heretofore, a disadvantage of growing from seed was the longer time period necessary until bloom - in many cases 2 years more than from other propagating methods. Under the lights, this time lag may be markedly decreased. My own record is a seedling of 'Llenroc' (a small leaf lepidote) that set bud 14 months from seed.
        Germinate by your favorite method. I happen to use a medium of sphagnum moss (brand name "Nodampoff") in small aluminum "Betty Lee" type food containers with clear plastic tops. I place the containers immediately near or under the lights. Sow the seed anytime; my advice is the sooner the better.
        Upon germination the containers are moved closer to the lights (6-12 inches) and hardened off as soon as possible. From here on the trick is to get them in 4 inch pots as soon as I can.
        When they have 1 or 2 true leaves they are pricked out and moved to plastic seedling flats in which they are spaced 1 inch apart. The growing medium here is still soil less - made up of equal parts of peat, perlite, and vermiculite.
        After about 1 month the seedlings are ready for 2 inch pots, into which they are individually transplanted. Here for the first time the mix contains soil. It consists of ¼th each peat, perlite, vermiculite, and potting soil. To this is added a sprinkling of superphosphate.  The final transplant is into a 4 inch pot (same mix) in which they stay until June or later, at which time they are ready to be bedded outdoors.
        WATERING, FERTILIZING:  The principles that govern watering and fertilizing are no different for plants grown under the lights than for outdoor plants. However, because under the lights the plants are in continuous growth, certain adaptations are necessary. A greater amount of watering will be necessary. Never let the pots dry out. On the other hand, a plant that drowns under the lights is just as much dead. A problem that might come up is from salt build up. While I cannot offer any set solution, frequent leaching and perhaps an occasional repotting will help.
        Fertilizing can also be tricky. Every time I think I have it solved something happens to put me in my place. A rule of thumb even under the lights: fertilize less than you think you should. I have run the gamut from the manures to the slow release chemicals. Right now I am back again to weak solutions of fish emulsions. Frequent applications where the medium contains no soil; much less so in other media. Watch your plants and let their appearance be your guide.
        This article cannot possibly tell you all you want to know. Its purpose is merely to make you aware of what you can do under the lights and hopefully to whet your appetite. I can only refer you to that cliché of what will happen if you try it. Of that I am certain!


Volume 32, Number 4
Fall 1978

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