Creating an Indoor Dahlia Growing Room
page two

Water is brought in from the rising main and fed through approximately twenty feet of copper pipe before it reaches the mist control valve. The idea is to bring the water to room temperature before misting the unsuspecting cuttings. The water is piped to the solenoid valve via a 150 micron filter removing any silt which might block the mist jets. The valve is controlled by a commercial box of electronics shown above, a sensing head is positioned eighteen inches above the cuttings and sixteen inches from the mist head.

The positioning of the sensing head is quite critical and is the most difficult part of the whole equation, as obviously it must be situated in such a way as to provide the necessary amount of mist, not too much and not too little.

The cutting medium is made up from half peat, one quarter coarse sand and one quarter vermiculite. The bed is kept at 70F by soil warming cables and the humidity is maintained at 62%. The first batch of cuttings damped off, the second batch suffered from mildew. The greenfly found the perfect haven and multiplied in their millions. Smoke candles eliminated the greenfly quite easily but the mildew was a different problem, I did not relish the idea of having to spray the cuttings at such an early stage in their development. Installing a small fan kept the air circulating and this had the desired effect of eliminating the mildew.

On average the cuttings root in ten days with the success rate being in the region of 95% for dahlias and 100% for chrysanthemums. As time passed I had to extend the bench area, which involved installing an additional Mercury lamp.

What seemed a simple enough task turned out to be a right headache.  As mentioned earlier the positioning of the sensing head is extremely critical, and incorporating the additional lamp into the equation added 400 watts of heat which in turn altered the day temperature, humidity and the mist settings. The solution was to knock two vent holes through one wall and install the fan on the opposite wall, allowing the air to come in at ground level and pass through the building to be extracted seven feet above the floor.  Day temperature is held at 62F and night at 52F. I will reduce both these by 2 degrees next year, I also intend reducing the daylength to 14 hours. No additional heating is required other than that radiated from the two Mercury lamps.

I ended up with two benches sitting side by side and occupying an area of three feet wide by nine feet long. A standard half inch plastic pipe carries the water from the solenoid valve down the middle of the benches to the three mist heads, and are positioned at a height of twenty-two inches above the cuttings.

The only improvement I would like to make here is to install an on/off valve on two of the mist standpipes. At the start of the season only one mist head is required, the other two being redundant. A means of turning them off would be desirable. All remaining floor and wall space is fitted out with Dexion shelving.

The mist electronics comprise a 24 volt solenoid to control the water reaching the mist heads, an electronic sensor (leaf) and a box containing the brain. There are four variables. (1) the position of the sensing head. (2) The sensitivity of the sensing head can be controlled to allow for light or heavy misting. (3) The duration of the mist burst can be adjusted over the range two to forty seconds. (4) The time delay between successive bursts can be varied between five and sixty minutes.

As the electronic leaf (sensor) shown opposite dries out it signals to the control unit and initiates a timing cycle, after ten minutes the controller energises the solenoid thus allowing the water to reach the mist heads.  The duration of the mist burst is set at 5 seconds and if insufficient water has landed on the sensor the process repeats until the sensor signals to the controller the cycle has been completed.  The whole cycle repeats about every 25 minutes during the day; at night the cycle automatically extends to compensate for the lower temperature.

The system being fully automatic it is possible to take cuttings, lock the door and return ten days later with an abundance of three inch pots secure in the knowledge that at least 95% of them will be ready for potting.

Indoor dahlia room Page three