By Peter Cole, 1995
You will need:
The propagator lids that I use are gabled with sliding, rather than circular ventilation slats made by Ward or Sankey, but other makes can doubtless be adapted. The ventilation is adjusted by means of a sliding plastic rectangle with slats that match those in the acrylic hood, which is retained by the raised plastic ridges around the ventilation slits. These are stocked by most garden centres.
The bulbs are of the type commonly sold as low-energy replacements for regular, incandescent domestic light bulbs, and may be purchased from hardware shops, department stores and even some supermarkets. These items are are readily available in the UK - I'm sure at least similar products should be available in other parts of the world.
1. Firstly the plastic slider should be removed - it will pop out if levered with a screwdriver - and may be retained for later use.
2. Next, score across the ends of the two acrylic strips in the ventilator - this should be done deeply on both the outside and inside of the lid at the point marked in Fig. 1.
3. Providing that the scoring has been done thoroughly, the strips may be knocked out with a small hammer or screwdriver to leave a squarish hole - insufficient scoring will lead to cracking in the lid.
4. If you try pushing the bulb into the hole, you will see that the central of the three plastic slider guides on both sides of the square prevents it from fitting, so with a pair of pliers or tin-snips, gently crunch down the ends of the overhanging plastic until the bulb may be slid into the hole - a file will also work but is much slower. It is important not to overdo this, as the secure fixing of the bulb depends on the slightly different width of the bulb and its plastic base. The bulb will fit into the hole, but the base will prevent it from falling in.
5. Now, take the plastic slider that you removed in step 1, and cut it in half along the centre slit. By carefully cutting a semi-circle on each side of the cut as in Fig. 2, the pieces may be trimmed until they may be clipped back into the slider guides around the circular bulb base. It is best to cut too small with a craft knife or tin-snips and then file into the final shape, checking regularly that you haven't removed too much plastic.
The slider halves may be refitted around the bulb securely, and will clip into the groove between the glass bulb and its plastic base.
6. using a suitable length of cable, make up a lead with a mains plug at one end and a lampholder at the other. If you are building a twin-bulb terrarium, a second shorter lead with lampholder may be wired into the first lampholder for a neater effect in connecting both bulbs.
If desired, the back and ends of the lid may be lined with cooking foil to increase the efficiency of the lighting without impairing viewing, and for all but the sweatiest of plants, the lid should be propped open an inch or so (I use matchboxes, but I'm sure a more professional- looking arrangement could be found.)
And Yes, you can make this in about ten minutes with a little practice.
Fig 1: close-up of ventilation slats: (in glorious asciivision...)
@+++++++++@@+v+@@+v+@@++++++++++@ ++++ - acrylic
Fig 2: the cut pieces of the plastic slider, ready to refit:
xxxxxxxxxxxxxxx xxxxxxxxxxxx xxxx - plastic
Lighting: one bulb or two?
So, you want to build the terrarium - but don't know which lights to use? I have successfully used a variety of makes, including Osram, Philips, and various stores' own-brands which commonly come in 11, 15, 18, 20, and 23 watts, ranging from 650 to 1500 lumens. These are composed of several tubes projecting from the base which may or may not be enclosed in an outer glass dome - the 23 watt ones are usually unenclosed (presumably they run a little hotter,) but this is not important to their operation, though it makes them a little more fragile.
I only use 15, 18 & 23 watt bulbs as 11 is too dim to be particularly useful, and 20 is not sufficiently different from 18 to offer any real benefit.
A single bulb will provide higher light at one end of the terrarium than at the other, allowing a wider range of plants to be grown together. As a rough guide to the light levels preferred by various genera, consult the chart in Fig. 3 -
Fig. 3: Suitable lighting levels for different plants:
(where x=bright end, s=shady end & xs=either. Obviously there is no shady end in a double bulb terrarium. This is assuming 3-side foil coverage to maximise light efficiency - adjust accordingly if uncovered.)
You may be able to guess why I like a single 23 watt bulb best - it's good for everything except aquatics ( algae hazard. ) Darlingtonia don't work well for me anywhere but outdoors, but of course YMMV with this as in all things.
And as I said at the beginning - "for low-growing plants..." This is not a suitable habitat for large neps, tall sarras or erect drosera, though it will double as a semi-heated propagator for seedlings. The lights are cool compared to incandescent bulbs, but will raise the temperature inside by about 10C over ambient. Sun-lovers like D. rotundifolia will happily sit directly under the bulb in a low pot or seed tray and thrive (though flower stalks are apt to go crispy if they actually touch the bulb.)
Timing: how much light do they want?
Theoretically your plants will expect a similar photoperiod to that which they would receive from the sun. However I have increased this with my own plants to 16 hours in the summer and 10 hours in the winter with very satisfactory results - in the Spring and Autumn adjust the time by 1 hour per week to change from winter cycle - summer cycle and vice versa, and everything should be hunky dory.
You can run as many terraria as you like (within the bounds of common sense,) from a single timer unless you require different photoperiods (I'm not aware of any CPs with unusual requirements, but some other plants, eg: kalanchoe, require strictly controlled lighting.)
Standard disclaimers apply - have fun, but if you're not sure of your electrical competence, find someone who is - I disclaim responsibility for fusing your mains supply or worse. Remember, water and electricity don't mix well, so make sure the bulbs are secure and the wiring is safe. I would also recommend using a plug fitted with a contact breaker to guard against possible mishaps.