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A Simple Guide: Closed Terrariums & Bottle Gardens

Updated: Mar 12, 2022

Here’s how to get started on building your very own closed terrarium or bottle garden, including the basic method for building one, materials, tools and a few plant suggestions too.

What you’ll need:

A gif of a terrarium being made step by step, from adding the soil, through to planting. | Garden Geeks UK
  • A container: Something you can seal and that isn’t too thin / delicate glass is ideal. Cork topped bottles, jam jars or Kilner style preserve pots are all perfect for creating your own little microclimate. You could also use a mini greenhouse, a glass lantern, lab equipment (if you're a mad scientist), or some of the many weird, wonderful and elegant terrarium style containers available on the market. Be creative!

  • Potting medium: Potting soil (obviously), you may also want to add other components to your soil such as perlite and sand (for drainage) or bark and vermiculite (for water retention) depending on the plants used.

  • Gravel / small stones / pebbles - for your drainage layer. You’ll want something of a size that can fit through the neck of your bottle/container. 5 - 20mm gravel is most common (depending on container size) and some variation in particulate size is always good.

  • Plants: Find suggestions below. Ideally, you’ll want plants that enjoy some humidity for a closed terrarium. Plants that grow compact, or can be pruned nicely are also good qualities.

  • Tools: There are many tools on the market ideal for terrarium building such as telescopic mini trowels and rakes, elongated tweezers and planting funnels. If you don’t have these, you can also make use of household items such as a trusty pair of chopsticks, a long paint brush, a funnel and your longest teaspoon.

  • Decoration: (Optional) Twigs, reindeer moss, cork wood, pebbles, miniature scenery - the possibilities are endless!

  • Optional: Activated carbon or horticultural bio char (charcoal), sphagnum moss, fine mesh/netting, critters.

Selecting your plants

A  colourful selection of red, pink and green Fittonia nerve plants | Garden Geeks UK

When selecting plants for your closed terrarium, you’ll want to look for those that enjoy a bit of humidity and moisture. Compact growers are also ideal to stop your terrarium from looking too wild or messy quickly and plants that can be pruned to stay bushy are also a quality to consider.

You might also want to think about getting a mix of plants with different coloured foliage or textures that compliment each other, or the look you’re going for.

Here’s a few beginner friendly plant suggestions:

  • Fittonia (Nerve Plant) – these humidity loving plants are available in a variety of fun foliage colours, perfect for adding a splash of colour. You can prune your nerve plant to keep them more compact and bushy if you wish.

  • Hypoestes (Polka Dot Plant) – similar to Fittonia, these guys are great for adding a splash of colour and will grow a little taller.

  • Pilea Norfolk (Friendship Plant) - relatively easy to propagate and care for with lovely brown, textured leaves.

  • Pteris ensiformis (Silver lace fern) - good for adding height and variation in foliage shape and plant type.

  • Pilea Cadierei (Aluminium plant) - this tropical plant loves humidity and will add some height to your display.

  • Cryptanthus (Earth Star) – Perfect for some colourful ground cover that isn’t just green.

Moss also looks great for ground cover, but may require some practise to keep happy!

Building your terrarium

You’ll want to build your terrarium in a series of layers to help create the perfect microclimate for your plants. It sounds complicated, but it’s all pretty simple really - putting things on top of each other as neatly as possible in a sensible order.

When filling your terrarium, make sure your countertop is clear – you don’t want a pesky pebbly cracking the glass. We also suggest placing it on a towel or mat for extra safety. The last thing you want is to put your lovely glass container down too hard and break it.

You should also wash out your terrarium and let it dry before planting.

Once you’re set, build your terrarium up in the following order:

1. Add a drainage layer

The drainage layer is important to make sure your plant's roots aren’t sitting in too much water all the time, which will make them rot.

Pebbles and gravel are commonly used for drainage layers, varying in size from about 5 - 20mm. Pick a size suitable for your container, which will cover around 20- 30% of your terrarium’s depth.

Before putting gravel or pebbles into your container, if you’ve taken it from outdoors, make sure to wash it - to remove anything potentially harmful to your plants.

When pouring the gravel in to your terrarium, do so slowly and tilt the container on its side a little, sliding the gravel down the edge (or use a funnel) gently to avoid cracking it. Use a brush or something similar to wipe any excess dust off the inside of the glass afterwards.

Optional extras:

  • Adding Sphagnum moss to the top your drainage layer will help soak up /retain unnecessary moisture, whilst adding variation to the particulate size.

  • Placing a layer of thin substrate mesh on top of your drainage layer will help stop your soil washing in-between. You could also use a layer of sphagnum moss for similar effect.

2. Add activated charcoal or biochar (optional)

Charcoal / bio char is used widely as a binder for toxins and impurities, trapping them due to their negative electrical charge.

  • Activated charcoal is a type of charcoal that has been treated at very high temperatures to make it more porous. The increased porosity of activated carbon/charcoal increases its surface area, helping it do its job more effectively.

  • Biochar is charcoal that is produced by pyrolysis of biomass (heating it in the absence of oxygen) and is often used as a soil conditioner. Similarly, its porous structure can help with water and water soluble nutrient retention, odour absorption and toxin trapping.

While not essential to your terrarium’s survival, adding about ½ inch layer of activated carbon / bio char to your terrarium on top of your drainage layer has the potential to help aid with water retention and filtration, reduce toxin/mould build up (which may incur root rot) and prevent unwanted smells from gas build up inside your terrarium. It’s also another variety of particulate size to help with drainage.

3. Add your planting medium/ soil layer

Before adding your soil layer, you may want to experiment with the positioning of your plants, though you can just freestyle it as you go. We find putting the soil in before the plants helps reduce the amount of mess on the leaves and up the side of your container.

Using a funnel or similar tool will help to avoid the amount of splashback up the side of your container that you’ll need to wipe up.

The exact type of planting medium you should use will vary slightly depending on the plants you use. However, in most cases it's beneficial to add some perlite to your soil, to help with drainage and aeration of the roots.

Adding some sand can also help with drainage, whilst bark can help with moisture retention and vary the particle size. Vermiculate can be added for moisture retention, though is less often required in a sealed terrarium as water is trapped within the closed system. Do a little research on your plants and find out what they like best.

As a coverall, adding 1/3 perlite to a 2/3 potting soil mixture is a safe bet.

A planted terrairum in a large glass jar at the Garden Geeks store. | Garden Geeks UK

4. Place your plants

Before putting your plants in your terrarium, you may want to get an idea of where they might sit. You could sketch out a rough composition, place them in their pots on the table roughly where you want them, or just go for it!

Some design tips

  • Generally, you’ll want to place taller growing plants to the back and shorter, bushier plants to the front.

  • Creating some asymmetry by having a taller plant or decoration on just one side can often work nicely too.

  • Choosing a variety of foliage colours and patterns that compliment each other will help pull your terrarium together

  • Make use of open space - you don’t have to crowd your terrarium. Leaving openings between plants and decoration can help create focal points and allow room for interesting growth.

When you’re ready, take the plants out of their pots and gently massage excess soil out of the roots / to free up any root balls.

Use your fingers (if long enough!), a microscopic trowel, chopstick or similar tool to make an indent in your soil to place the roots in and then cover them up. You may need to add some excess soil around the base of the plant to help stabilise it.

Remember to leave room for growth in your terrarium, so try not to overcrowd it from the get go. In some cases you may need to split larger plants up.

Once all your plants are placed, fill any gaps with soil and give it a gentle pat down to help level it out.

5. Add some decoration

How you decorate your terrarium is up to you. Whether you want to go el natural with sticks and stones; make your own miniscape with teeny tiny ornaments; or create a theme around which to base your biome, adding some decoration can really help set your terrarium off.

Here’s some ideas:

  • Colourful or polished stones and gravel add some glamour and can be as natural or as vibrant as you like and also help stabilise plants in the soil.

  • Sticks, shells, cork wood and other such items can add interest and height, and be a surface for moss to grow on or plants to climb up if included

  • Miniature items can help add a sense of scale to your mini world - what about a mini buddha or pagoda for a zen themed terrarium, or tiny creatures to create a miniature rainforest?

6. Add some water to your terrarium

Finally, you’ll want to add some water to your terrarium. Rainwater is preferable and if you don’t have that, let some tap water sit for 24 hours if possible.

Water until you start to see liquid slowly draining down to the first layer of drainage gravel.

7. Add some critters (optional)

Not essential, but something for the more inquisitive or advanced terrarium builder to try, critters can be a fun and beneficial addition to a terrarium.

  • Springtails are your own personal clean-up crew and can help aid with decomposition and debris in the soil. Springtails are detritivores and feed on dead organic matter, such as dead leaves and roots. They also enjoy eating mould too! A great starting point for building a bioactive terrarium.

  • Woodlice work well together with springtails and perform a similar function but - being much larger - are easier to spot if you’re wanting to add some visual curiosity to your terrarium. You will however need to ensure humidity is high enough in your terrarium to keep these isopods alive.

8. Put a lid on it!

An upwards shot of a planted glass jar terrarium in the Garden Geeks store | Garden Geeks UK

Once you’ve built up your drainage and organic layers, added plants, decorations and maybe even a critter or too and then watered your terrarium, it’s time to seal in your little ecosystem.

It’s important to get a relatively good seal to keep moisture from entering and escaping, so that your own little environment starts circulating within itself.

Try to resist the urge to remove your cork, lid or seal too much, unless maintenance is required.

Sit back and admire your creation!

Terrarium Maintenance

The joy of a closed terrarium is that it shouldn’t need too much maintenance given the right spot and components.

  • Keep your terrarium in a bright spot but away from direct sunlight.

  • A completely enclosed terrarium requires little to no watering, but if in doubt always water less.

  • If soil is completely dry and leaves are wilting, add a little water using a mister. Avoid pouring water into your terrarium once it has been made.

  • Condensation build-up on the glass of your terrarium is natural, however, if it is seeming very wet, you could try opening the lid and ventilating it for few hours. This is also a good time for maintenance.

  • Check on your terrarium every so often to see how it’s getting on and try to avoid opening it any more than once every 2-3 weeks unless necessary.

  • If you see any dead or dry leaves, remove them during maintenance to avoid the unwanted spread of mould or fungus. If you’ve got critters in your terrarium, they’ll help deal with this for you, so don't remove all their food!

  • If you plants are growing a bit wild, you can prune some of them to keep them nice and bushy, if the plant is suited to that.

Remember… have fun!

Terrarium building is all about trial, error, patience and having fun. Sometimes things just might not work out and you’ll need to start over, other times you might be surprised at how your initial attempt grows into something great.

Experiment with different designs, different plant combinations and different locations for your terrariums until you find something that works for you.

Most importantly, remember to have fun while doing so. It’s your one chance to be the ruler of your own little world and contain your desire to be a megalomaniac into a bottle with a cork in... safely away from everyone else.

Have fun you green fingered world builder you, just don’t let the power go to your head too much!

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