First of all let me say that I am a complete novice as far as dahlia growing is concerned, as I only started growing these exotic flowers in 1991. 1 therefore have no previous knowledge on which to base any of my experiments which may or may not be an advantage.
I was employed by the government as a telecommunications engineer and dabbling with electricity and electronics is second nature to me.
I propagated my dahlia cuttings by conventional means for the first year but year two was slightly different. I purchased a 400 watt Mercury growlight which enabled me to bring the season forward. I wanted to rear other plants apart from dahlias and being confined to a small greenhouse the light would allow me to stagger the seed sowing. This arrangement proved to have limited possibilities, what I really wanted was total control.
Following on from these first experiments I will attempt to outline the progress that I made with propagating under totally artificial conditions and hopefully help anyone contemplating such a setup to avoid falling into the pitfalls. I started off in August 1994 by constructing an area 18 x 10 feet inside an old poultry house. The walls and ceiling are lined with glasswool, the internal surface of the walls are lined with asbestos sheeting and the ceiling lined with Gyproc backed by an aluminium foil. All the internal surfaces are painted white to assist in light reflection.
Having attended several lectures on the topic it became apparent that most people were using Growlux tubes which are obtainable from any pet shop. Not having any means of measuring the light intensity I decided against using such tubes in such a large area. They do have their use but mounting them twelve inches above my cuttings was not going to work because I intended using a mist system and it is a well known fact that water and electricity don't mix.
The Mercury lamp is
controlled by a time clock, the lamp dissipates 400 watts of heat
and by calculation it was estimated that no additional heating
would be required during the artificial day. However two tube
heaters were provided for night heating; should they be required.
The first obstacle was to decide on how many hours light the cuttings should receive, not knowing when the plants would be transferred into the natural daylight. I decided to be on the safe side and adjusted their length of day to seventeen hours. This was actually two hours longer than required because the natural day was fifteen hours when the plants were moved. The result was I had to supplement the additional two hours by using Growlux tubes over the plants for a few days till I thought they had become acclimatised. I should mention here that the lamp is seven feet above the floor level providing a seven foot circle of light.
P.S. the daylength was subsequently reduce to 14 hours and I have kept it at that for the past few years.