I recently built a closed bottle terrarium for my girlfriend. It's a closed system which can last months, years, sometimes even decades without human intervention if you get the ratio of materials right.
The idea of a closed system is that the plants inside are basically in a state of suspended animation - they don't grow, only... live. They get their energy from sunlight which they convert into necessary materials, and they recycle their water and air. Only bigger plants in bigger bottles can last decades, but with a bit of help, small ones can live a long life, too.
Here's a picture of the final product:
If you'd like to build your own, here's the full process, with pictures.
Things you'll need:
- sealable bottle (cork, seal, etc.)
- wired coat hanger will be useful for tall/narrow bottles
- planting dirt (buy at florist - nutrient rich dirt is important)
- active charcoal
- water spray
- cotton or cloth for cleaning the bottle on the inside once all is done
- optionally: decorations (see step 1.5)
Prepare your tools
The coat hanger will have to be destroyed. By leaving one of the corners intact and cutting it in the middle, you can actually make a neat pair of pincers:
Additionally, the rest can just be straightened out and turned into a "curved prodder" - a bent piece of hard wire you can use to poke and prod the plants and dirt even in the edges of the bottle, if the neck is narrow. For added effect, make its pointy end thicker by using sticky tape, cotton, or anything else that'll stay attached.
Make sure the water spray is SUPER clean and free of any chemicals. Rinse it thoroughly in boiling hot water if it contained anything else before, and do a hundred or so squirts of boiling water before you put water for the plants in.
Step 1: Get and clean a bottle
The more unusual the bottle, the better the effect. Clean the bottle, let it dry (for best effect wipe off the inside with cotton balls on a stick or a piece of cloth) and make sure to properly remove any external stickers before you start filling it.
Make sure you have a cork, or any other way to hermetically seal the bottle once it's done. You want to close that ecosystem as soon as possible after it's made.
Step 1.5: Decide on a theme [optional]
Sometimes, it's cool if bottles have a theme. Grab a small Lego sword, make a rock out of clay and put it in there, paint it silver/gray, and you have a tiny Excalibur.
Get red pebbles (more on pebbles below) and red plants (more on plants below) and have Mars in a bottle.
Put a little dinosaur in there with ferns, and have a prehistoric scene.
Or, like I did in this case, leave it generic and let the bottle itself be the decor.
Step 2: Pebbles
Pebbles can be purchased in pet stores as fish supplies (aquarium decoration), or just go out and find some. Any combination of color / size works. I went with white, the size just enough to fit through the bottleneck.
Pebbles serve as a drainage system. That's where the excess water will flow to and filter through, so the plants don't end up in a bottled-up swamp.
Step 3: Active Charcoal
Active charcoal (yes, the stuff some people rub on their teeth to make them whiter) can also be bought in pet stores as a fish supply - people use it in water filters for fish, and it has the same purpose here. It'll filter the air and water, and keep the ecosystem healthy longer.
Use a small spoon to distribute it evenly, and if you don't have a funnel, a rolled up piece of paper will do fine for any kind of narrow bottleneck.
When trying to get it distributed evenly, tilt the bottle to the side if the neck is narrow. This will cause the coal bits to naturally bounce off and evenly spread out. Don't worry too much about it, entropy will take over and they'll mostly fall into place. Alternatively, use a chopstick or the hanger prodder to scatter it from the center pile, if that's how it fell.
Don't overdo it.
Step 4: Moss time!
It's time for moss. This layer of moss is a foundation which keeps nutrients from falling too deep into the pebbles, and prevents dirt from crumbling in there and making a mess.
You can buy moss at a florist, or you can pick your own (pick the ones on the ground, not on the trees). In the picture below, the moss on the left is dehydrated, purchased moss. The moss on the left is freshly picked from a forest.
I used a combination of both, but for the first layer, mainly the left one. The left one has fewer active roots, and as the first layer doesn't need to plant itself into anything but is basically a "carpet", it fits the purpose nicely.
Note: if you buy dehydrated moss, you need to activate it first. Put it in a container like in the picture, and spray it with the water sprayer until moist. Cover it, and leave it like that for a few hours - preferably over night. That'll give critters a chance to emerge, and you'll easily see if it needs more or less water.
Cut off a piece of the moss approximately the size of the bottle's widest area.
Then, shred it into smaller pieces and use the pincers to slowly position the moss evenly on top of the charcoaled pebbles.
Prod it with the prodder into the corners if needed until you get an evenly covered surface.
Step 5: Dirt
This is arguably one of the more frustrating parts. Not only does it take long to do right, but it also uglifies your terrarium, which until this point looked rather good.
It has to be done, though, so grab the funnel and start scooping dirt into the bottle on top of the moss. A 1cm layer is enough (it looks like more in the picture because the moss is holding it up).
Do this very slowly - the less you get stuck on edges (another big advantage of having a super-dry bottle), the less you have to clean later.
Step 6: Plants
I used just some basic ferns here, but a lot of plants will work well - even some flowers like African Violets which have the uncanny ability to reproduce asexually, so you can grow them by cloning.
There's no special trick in preparing the plants - make sure they have their roots when you pick them, and try to jam them into the dirt as much as possible, while being gentle about it. Use the pincers to place them, and the prodder to direct them and to straighten the leaves. It's okay if they have some of their own dirt on the roots - even better in fact.
Step 7: Moss again!
Finally, we put in the last layer of moss. This moss is for decoration, and for fixation. If the moss has some roots and dirt, even better - this is where I used the wet, forest moss a little more. It'll tie everything together by binding with the plants, the dirt, and the moss underneath, and it'll hide the ugly dirt.
In narrow bottles, this is extremely frustrating - just stay patient. If you end up breaking or covering some of the plants (can't be avoided, it'll happen), use the prodder to set them free, or if it's not possible without accidentally breaking something else, leave them. With sunlight and as they get acclimated to their new environment, their strength should return.
Step 8: Cleaning
Before corking it up completely, we need to clean the bottle. It's easiest to do this by wrapping a piece of cloth or cotton around the prodder's thick end, and just wiping the glass walls on the inside, while being very careful about the plants. A dirt speck or two is better than a broken or unrooted plant.
Step 9: Wrap it up
Finally, cork the bottle, put it in a well lit place but out of direct sunlight (you don't want to cook your plants), and observe. You generally shouldn't have to touch the cork unless you see an excess of moisture inside (more than dew on the walls) or bugs that crawled out of the moss - in either case, open it up a bit until the moisture evaporates a little / critters escape, then close it up again.
I'm still a newbie at this, so please shoot any advice you might have at me in the comments below!