By Robert C, Extension Master Gardener Volunteer, Pitt County Arboretum
A terrarium is a beautiful miniature jungle for your home contained in a bottle. It makes a great conversation piece and requires minimal care. It needs watering once a month, once a year or even longer periods, depending on its design. It likes a little sun but too much as it gets hot inside the bottle.
Here is an example of an established terrarium. It was easy to build and this blog is going to describe how to make it. We’ll list some suitable plant choices at the end.
5 or 10 gallon bottle
Cork or stopper (optional)
Paper - make a wide mouth funnel from the paper
Spoon taped to a bamboo stick
Worm castings (optional)
Potting or terrarium soil
4 or 5 plants
The bottle can be glass or plastic and should have a neck large enough to drop 2 inch plants through. This example used a 5 gallon plastic brewing carboy.
This can get a little messy, so you may want to do this at an outdoor table or have lots of newspaper lining your worktable.
Make a funnel from a newspaper or construction paper. The narrow end of the funnel should be slightly smaller than the bottle neck. Materials will be dropped into the bottle with the funnel and the funnel can clog if the neck of the funnel is too small. The bamboo stick can be used to coax material in.
Drop in a layer of pebbles that is about ½ to 1 inch thick. Aquarium pebbles come in a variety of pretty colors. The purpose of this layer is to act as a drainage water reservoir.
Use the paper funnel to guide the pebbles in. If your bottle is glass, be careful not to add pebbles too rapidly as the repeated “drip” of rocks can shatter the glass.
Use the spoon taped on the end of the bamboo stick to level the pebble layer.
Next add a layer of activated charcoal. This acts as filtration for the water.
We want to stop the dirt from working its way in to the pebble basin and we can do this by cutting a window screen to size. It will act as a barrier between the water reservoir and the dirt.
The screen can be rolled up and dropped through the bottle neck and then use your spoon-on-a-stick tool to open up the screen and position it on top of the charcoal.
Mix the worm castings (optional) and potting soil and drop the dirt. Follow the packaging instructions for the ratio of castings to soil, but a rule of thumb is about 10 parts soil to 1 part worm droppings.
Use your paper funnel to drop the soil mixture in to the bottle. It will pile up in the center and you can use your spoon-on-a-stick tool to spread the soil evenly.
You want about 2 to 3 inches soil layer. It will be very loosely packed, but over time the plants’ roots will firm up this layer.
You are now ready to plant your plants. These are in 2 inch pots because you need to drop the plant through the bottle neck and larger plants will not fit.
A 5 gallon bottle can comfortably have 4 to 5 plants. You want to plant on the outside edges of the bottle first because dropping a plant in falls in the center. The last plant can be planted in the center of the bottle.
Decide on your plant arrangement and then using your spoon-on-a-stick tool, dig a shallow hole where you want the plant to go.
Drop your plant in to the bottle. Be gentle with it fitting it through the bottle neck. The root ball in a 2 inch pot can be coaxed to slip through the neck. It will fall to the center. Use your spoon-on-a-stick tool to push the plant into the shallow hole you dug and manipulate the plant in to an upright stance. Gently push dirt over the roots to cover them.
Repeat the process for the next plant – dig a hole, drop it in, maneuver in to place and cover the roots.
If there is room, the last plant will be planted in the center of the bottle.
With all the plants in place, you are ready to water the terrarium. Depending on the size of the bottle, ½ to 1 cup of water will suffice. Carefully tilt the bottle and pour the water so that it flows down the side of the bottle. That will add the water without hurting the plants. You can aim the water flow to rinse the side of the bottle where some dirt may have stuck to. Alternately you can wrap your spoon-on-a-stick tool with a damp paper towel to wipe down the sides.
The cork/stopper is optional and will change how often you need to water. With no cork, the water evaporates out of the bottle and you will require to water about once a month. If you put a stopper in then the water is retained and you may not have to water for a year or more.
Care for your terrarium is simple. A little sun is ok but not too much. It gets very hot and humid in the bottle, which some plants may like and others not.
Turn the bottle to change the facing towards the light. This helps the plants to not lean too much in any direction.
Watering is infrequent and you can control the humidity level by putting the stopper in or not. Ideally you should see condensation in the morning and evening. If there is none, you need to water. If there is condensation throughout the day, then there is probably a bit too much water. It is easy to reduce the water in the reservoir by removing the cork. This will over the course of a couple of weeks drop the water level. When it is less humid you can replace the cork.
Your plants will start to grow and over time, some of the leaves may die off and decay. There may be algae. There may be mold. You need a cleanup crew. Once the terrarium is established you can add spring tails Folsomia candida to the bottle. These small (1 to 2 mm) moisture loving insects are harmless to people and feed on the decaying roots and fungi and rarely damage plants. They will help control mold issues in the bottle.
Plant Choices for Your Terrarium:
Photos from the NC Extension Gardener Plant Toolbox