Obviously, this is not the first terrarium-themed instructable. Inspiration came from noahw's DIY Terrarium instructable, along with ThinkLem's Lightbulb Terrarium and alisha145's Tiny Terrariums. However, I think the wine bottle idea might be a first!
Step 1: Bottles
Your bottles will probably needs the labels removing. Labels are either stuck on with water-based or solvent-based glue. Unfortunately one needs a lot more work to remove than the other.
Start by soaking the bottles in hot water (but not boiling hot as this could crack the bottles) for a few minutes. Labels glued on with water-based glue will either soak off in this time or some gentle pushing with a paint scraper will do the trick. For labels stuck on with solvent-based glue, scrape away as much of the paper as possible (ideally all of it) and give the bottle a rinse. To remove the gummy residue from the solvent-based glue, I used acetone (it's also in nail varnish remover but less concentrated). Practically anything that will dissolve plastic works, although you could just buy some de-gluing stuff from your local hardware store.
Step 2: Drainage
I used some gravel (from the drive) and some builders' sand we had lying around. The gravel creates a reservoir in the gaps between the stones whilst the sand stops the earth from falling into the holes.
You want a decent amount but not too much (about 2 inches or 5cm), bearing in mind that you need to add earth and that there needs to be enough room for the plants to grow.
Step 3: Compost
If you plan to use seeds, leave some of the soil out so you can cover them after the next step. The same also applies if you are using small seedlings or plants.
Fill your bottles with about 2-3 inches (5-7.5cm) of soil. Give it a slight shake or tap to level it out.
Step 4: Planting
For seeds, just sprinkle a few into the bottle and cover with a little extra compost.
These can be difficult, and so there are a number of different approaches:
1) If you have some very long tweezers or other similar instrument, you can simply push their roots down into the soil.
2) If their roots came in a block of soil, you may be able to get the block of soil inside intact, and then you can fill around it with compost. In this case, you should do this just after adding the sand to leave enough room for the plant to grow.
3) If you feel adventurous, you can drop the seedlings straight in and add more compost on top. It is highly likely that this won't work or will look very ugly, but mother nature may sort things out (eventually).
We also made a bottle with an ash sapling that we found in the garden. It was quite big which was a bit of a problem and so we added it right from the start which in hindsight was probably not such a good idea. Tree saplings will vary so I leave you to discover a method that works for your bottles and the size of whatever tree sapling you happen to have.
Step 5: Care
The bottles won't need much watering over time as the relatively closed nature of the bottle means that most of the water will cycle back. A bit of plant food every now and then might help as the nutrients in the compost will be limited. Make sure that whatever plant food you use is suitable for what you've planted though.
Now it's time to sit back and watch your plants grow!