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20 March 2018

Part 2: Succulent Terrarium: DIY

Part II: Succulent Terrarium Construction

Exactly what will it take to build a succulent terrarium that will not eventually succumb to the serious and fundamental flaw in the very idea of putting succulents in a terrarium?


First things first:
If you have not read the introduction to this project, go back and read it first; the succeeding discussion will not make sense otherwise.


To summarize, though, our succulent terrarium will have to provide the following conditions in order to succeed for longer than two weeks:
          1. air movement
          2. low humidity
          3. very short wet-pot period (i.e. rapid evaporation)
          4. rapid drainage
          5. high light conditions
          6. heat
Why? Because evolution. See related post.


Materials and Preparation
To try and achieve all that stuff I listed above, just off the top of my head, we need the following materials:

  • Sealable container, typically glass. But for this project, for ease of demonstration, I'm using something plastic and easy to cut
  • Sterilized potting substrate; typically just soil. But since we're planting succulents, we will use pure pumice.
  • Some kind of cutting tool, a box cutter, say.
  • Computer case fan
  • Sacrificial succulent plant.
  • Hygrometer
Step 1: Cut an opening on the lid of your terrarium jar. This is hard to do with glass so if you are using glass, I recommend instead to get an acrylic sheet. You can get a 12-inch square of the material which is also available in various thicknesses. Then cut it down to size so that it is flush against the rim of your jar or container. After that, cut a hole so that the case fan will fit nicely.
So, now we have a nice container with a fan on top of it for fresh air to be blown into the plant. For this project, I used a 120-mm case fan plugged in to a 12-volt USB socket.

The intake, however, will need an out. I want to airflow to come from the top and exit as close to the top of the soil line. The idea is to also ventilate the pumice and help it dry out faster. So, windows! And since growing medium for succulents also need to drain fast, this baby is going to need a drainage hole. If I don't put a drainage hole, that water will sit there and eventually drown my succulent.

So, why don't I just NOT water the plant, then? Why not just spray it carefully so that it gets moisture just enough to water the plant but not so much that the fan can not dry it out? Well. To start with, that will require uncorking the top to get the spray in. Worse, though, it will get the plant leaves wet---something you don't want to do to a succulent even when it isn't in a terrarium. Succulent plants have a rapid and exaggerated response to water so you don't want to trip off that response every time you water such a contained environment.   
So, I cut four holes at the bottom of the container and two holes on opposite sides just above the line where I plan to fill it up with substrate.

To maximize the air intake, I decided to seal the mounted case fan onto the lead using hot glue. Filled up to the appropriate depth with substrate (akadama, in this case, because it is what I have), here is finally what, in theory, a viable succulent terrarium should look like.

This case fan will now have to be connected to an 12-volt DC adapter and ran 24/7. 

Now, imagine you had to do this with a glass container. Imagine further the lensing effect of glass and how it is likely to fry the plant inside. This means that if this terrarium had been glass, it will have to stay out of direct sunlight. Given that it will not get as much light that most succulents need, whatever plant will go into such a jar will etiolate (i.e. stretch out towards the light instead of growing compact).

So. I'm going to look for a disposable plant (turned out I don't have any) that I can test this thing with. To be furthered!

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