12 March 2018

Q&A: Part 1: How do you make a succulent terrarium?

This blogpost will probably offend you so stop reading; this is going to be a snarkfest.

It is impossible to tone it down because...well, succulent terrariums. This is by far my favorite idea to filter down from the Flakeworld, along with crystal therapy for cats, and homeopathy. And what's not to like? The photos are always beautiful, elegantly understated, evoking thoughts of sunny skies and youthful sparkle. And they look like they take care of themselves!

But, like all well-packaged bullshit, you don't realize you're chewing on fecal matter until you've swallowed it.
This one, for example, was being sold for $125. It is, without a doubt, at once breathtakingly beautiful and inevitably fatal to the plant. Know that whenever you buy one of these things, you're paying for the gesture, not the idea.

Then, there is this mass-produced abomination that takes the concept out of the hands of casual hobbyist to a different level: the mass market .I applaud the creativity, but if these are being sold as anything other than succulent plant coffins, that's just rude.
Let us start this conversation by trying to reach an agreement on exactly what a terrarium is. This is not a matter of opinion. "Terrarium" is a word that means something specific and it is this: an enclosed container with plants in it. 
This is what a successful terrarium looks like.

Pictured here is David Latimer from Cranleigh, Surrey (Daily Mail UK), with his bottle garden that was reportedly planted in 1960 and has not been watered since 1972. This is the quintessential terrarium.

The idea is to put plants in a sealed container so it can be grown in a controlled environment. People who like jungle plants have to do this in temperate or dry regions where humidity fluctuates down to near-nothing. A sealed terrarium will maintain high humidity and if placed somewhere appropriate, will remain warm even without heating. The plant goes about its business and once the correct balance of nutrients and moisture has been achieved, it settles down to its own rhythm and you can pretty much leave it alone. It has reached homeostasis.

Over time, people started making what they call "open" terrariums to make things less stressful. Sealed terrariums are trouble-free when they succeed but getting them to that point is not easy. Open terrariums require constant care but it spares you from start-up failures. Even open, it still achieves much of the primary goal of terrariums---high humidity and heat. These open terrariums are typically open jars, fancy globes and open fishbowls as well as leaky glass boxes. They are enclosed but not sealed. These are typically easier to maintain because it makes the plants accessible and easy to troubleshoot. Every time you open a sealed terrarium, you are basically restarting the process of reaching the appropriate equilibrium described above. An open terrarium does not have to reach that equilibrium, you just have to keep fixing it if it tilts out of whack.

Found on a website called notonthehighstreet; being sold as a terrarium. These are actually skull shot glasses and they look pretty cool filled with orange juice or some nice brandy.
That, however, is where the word-stretching has to stop. I have seen blog posts about filling a brandy glass up to to the rim with potting soil, plopping random plants in and calling it a terrarium (see photo above). What that is, in fact, is a glass pot without a drainage hole. So, not a terrarium.

Central to the concept of a terrarium is the idea of it being enclosed. There is some stretch room there but the stretch can only go so far before the object you are describing ceases to be a terrarium and becomes something else. If the plant is not in any form of enclosure, it's in a fucking pot. 

The second important concept here is succulence. Orchids, for example, are not succulents. With the exception of severe outliers, they evolved in some of the most humid environments on the planet. They are constantly moisturized and very often showered by frequent rainfall. They do well in terrariums as a result. Also as a result of their native habitat, orchids have ways of regulating water intake so they do not drown in the monsoon. But even with that mechanism, you don't find orchids in freshwater lakes. Regardless of how humid and wet it is in tropical jungles, they will still drown in a tub of water. Orchids are not kelp.

Directly opposite to orchids are succulents. These are plants that over thousands of years have evolved many strategies for surviving low-water environments. These are plants differentiated by their greed for water. They suck it up and store it. Water comes by so rarely in their native habitats that a lot of succulents have to go to extremes to access and store it. That ability to store water is why most of them have plump leaves or fat stems. It lets them survive for a long time without water. Their reaction to moisture is to absorb absorb absorb. This is why an over-watered succulent dies seemingly within hours. Once they reach the limit of their ability to store water, their cells just burst.

Finally, one last point---succulents are perennial. They do not renew every year like rice or sunflowers. Most of them need years to even reach mature reproductive age, in fact. When water is scarce, you just won't have the resources to do things rapidly and start over every year. You need years.
Haworthia cooperi var dielseana I have had this plant since January 2011. One of the fastest way to kill it is to put it in a terrarium.

This is why the most earnest and serious succulent growers will talk to you in terms of years and sometimes even decades. These growers are not interested in having a globe of echeverias for two weeks. Creds are earned by how long you've kept a pot of adromischus alive and "how long" is counted in years, not months.

You are now probably beginning to suspect that putting succulents in a terrarium is not the brightest idea.

But as a thought exercise, let's still ask---exactly what will it take to make a successful succulent terrarium that will last--not weeks--but possibly years?

I have used glass containers to build sealed terrariums before---large apothecary jars, gigantic mason jars and even flower vases that is then sealed with clear acrylic disc. I have an active and ongoing fish tank that has filled up with episcias twice and had to be depopulated. For the purposes of this blogpost, though, we will work with a plastic jar for reasons that will become apparent later.

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 above

Materials and PreparationTo 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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