If there’s one thing in common with every terrarium, it’s the false bottom. And there’s a good reason for that: it’s a critical component that’s necessary for the long-term survivability of your terrarium.
A false bottom or a drainage layer comprises the lowest part of your terrarium. It’s purpose is to provide a drainage area for water to flow out of the substrate, preventing your plants from developing root rot due to stagnant water. Most false bottoms can be made of rocks or one of many other materials, each with its own pros and cons.
In this article, we’re going to get through everything you need to know to design and build your false bottom for your terrarium from scratch.
Table of Contents
What is a false bottom?
The false bottom (also called a drainage layer) is the lowest layer that goes into your terrarium. The purpose of the false bottom is to provide a space for water to drain away from your substrate.
There’s really nothing special about it, in that it doesn’t magically give your plants special nutrients. The only thing that is doing is providing empty space for water to drain into.
By allowing water to drain away from your substrate, you are doing a few things:
- You minimize the chance of your soil turning putrid and getting issues like root rot and mold
- You give yourself a greater margin of error when watering your terrarium
- You create a space for water to accumulate away from your plants, allowing for high humidity levels in the terrarium without over-watering your plants
- When water exits the soil, air moves into the space left over, aerating the soil
Conceptually, the drainage layer mimics the natural water cycle that plants have adapted to in their natural environment.
In nature, rainwater that lands on the soil either evaporates back into the atmosphere or moves across, through, and out of the soil due to the pull of gravity. This movement of water aerates the soil by allowing air to fill in the space where water has drained from the soil, allowing plant roots and many organisms in the soil to have access to oxygen for respiration.
This natural phenomenon is so critical to plant health that societies throughout history have engineered and designed surface drainage systems for agricultural practices. It’s still being done today in modern farms with a tool called an aerator.
My thought is that if those guys who have accumulated thousands of years of farming knowledge are doing it, I should probably do it too (although on a much smaller scale).
How do you make a false bottom in a terrarium?
If you’re completely at a loss of where to start, here’s a quick step-by-step low budget guide you can follow:
- Get a container for your terrarium. Check out this post if you want my recommendations for containers
- Gather some rocks/pebbles or choose a different material from the table I have later in this post
- Get a plastic bag or another separation material from my list later in this post
- Cut the plastic bag or separation material into a shape slightly larger than the shape of your container
- Use a toothpick or pen to poke a bunch of holes in the plastic bag. Skip this step if your separation material already has small openings
- Add the rocks to your container up to about an inch high
- Cover the rocks with your separation material
- Pat yourself on the back for completing your false bottom and proceed with building the rest of your terrarium
There’s no one single way to make a perfect false bottom in a terrarium. As long as you are fulfilling the purpose of the drainage layer by providing space for water to drain from the soil, you’re doing just fine. Whether that’s with low budget or higher budget materials, both will give you great results.
That being said, most false bottoms will have a similar structure with these characteristics:
- Made of pebbles, rocks, or other small, hard material usually with inconsistent/non-uniform shape
- Are at least a half inch or more in depth
- Consists of a sturdy, water resistant, stable structure
- Made of Inorganic, synthetic, and/or man-made material
Those characteristics are by no means all 100% must have requirements, just general rules of thumb. I’m sure there are probably exceptions out there. So don’t be worried if you are thinking about using something that doesn’t check every single one of those items, feel free to just give it a try!
That should give you a pretty high level understanding of what a false bottom is and how you can make one. In the rest of this post, I’ll go over each of those points in finer details in case you’re curious.
What material should you use for a false bottom?
You have a lot of choices when it comes to what material you use for your false bottom. To help make that choice a little bit easier for you, I’ve put together a list of all sorts of materials you can choose from, their rough cost estimates if you were looking to purchase them, and their pros and cons in the table below.
| Material | Cost / cu ft | Min bulk price | Pros | Cons | Source |
|---|---|---|---|---|---|
| Egg crate | $5.55 | $16.65 / 4'x2'x0.375" panel (3 cu ft) | -Cheap (by volume) -Maximum drainage -Lightweight -Retains shape | -May not be aesthetically pleasing -Requires cutting and/or zip-tying | Home Depot |
| landscape rocks | $10 | $5 / 30 lb bag (0.5 cu ft) | -Cheap -Looks natural -Easily obtainable -Can be gathered for free in nature | -Somewhat heavy -May require rinsing | Home Depot |
| Sand | $10 | $5 / 50 lb bag (0.5 cu ft) | -Can be gathered for free in nature -Cheap -Looks natural -Can use without separation material | -Water may soak back up into substrate -Does not provide maximum drainage | Home Depot |
| Perlite | $19 | $5 / 8 qt bag (0.27 cu ft) | -Some of this can be added to soil to: -Improve drainage and aeration -Prevent soil compaction | -Might give your plants fluoride burn if in contact with roots | Home Depot |
| LECA / hydroton | $22 | $39 / 50 L bag (1.76 cu ft) | -Tough -Can retain water to increase terrarium humidity -Can also be used in plant soil | -Bulk price may be expensive | Home Depot |
| Filter floss | $24 | $12 / 12"x72"x1" roll (0.5 cu ft) | -Filters water passing through -Easy to cut and shape | -Might not retain shape | Amazon |
| Foam pond filter | $30 | $14 / 23.6"x17"x2" cut (0.46 cu ft) | -Easy to use -No separation material required -Easy to cut/shape | -Might not retain shape | Amazon |
| Turface | $45 | $6 / 4 qt bag (0.13 cu ft) | -Holds moisture -Provides great drainage -Adds acidity to water | -Pricey -Not abundantly available | Glassbox tropicals |
| Aquaponic substrate | $120 | $16 / 1 gal bag (0.13 cu ft) | -Lightweight -Looks natural | -Must buy online -Pricey -May affect water pH levels | Amazon |
| Charcoal | $160 | $8 / 2.25 qt bag (0.08 cu ft) | -Purifies your water and air from toxins and chemicals -Reduces odor -The best material money can buy for your terrarium health | -Pricey -Might be a little messy | Amazon |
| Marbles | $593 | $9 / 100 0.64" marbles (0.015 cu ft) | -Looks cool -Maintains shape long term | -Expensive -Your child may choke on them | Amazon |
I listed two columns for cost: one for cost per cubic foot and another for the minimum bulk price. You are probably not going to find any material you can just buy a small handful of. Your supplier is probably going to sell them in big bags, likely way more than you’ll ever need. So I went ahead and listed the price you’ll probably end up paying if you want to go shopping and buy some.
If you’re looking to buy some for just one terrarium, I would sort by the minimum bulk price. That’s going to give you the lowest price for the short term. If you’re looking to make a whole bunch of terrariums or have a very large container to work with, I would sort by cost per cubic foot to get you the lowest price in the long run.
Honestly, I was struggling when coming up with the list of cons for the table. It’s really hard to go wrong with your choice of drainage layer material. Pretty much any material in the list up there will work just fine. Even materials that I didn’t list up there will probably be fine for you as well.
As long as it doesn’t decompose or fall apart in water (like wood, metal, or a bunch of paper towels), it’s probably fine. You’re mainly just looking for something relatively sturdy and will hold its shape for a long time. You don’t want to get something that’s going to collapse on itself after getting a little wet. The false bottom is the foundation of your terrarium after all and will have to support the weight of the substrate and your plants above it.
My go to option is to use some kind of rock or pebble. Usually these are easily gathered in nature or can be bought for a pretty low price at most places while still performing the function of a drainage layer.
How deep should a terrarium false bottom be?
The depths of your false bottom will depend on the size of your terrarium, but for most people, 0.5 to 1.5 in will probably be sufficient. If your terrarium is on the larger end, you’re going to want to make your false bottom a little bit deeper. If it’s on the smaller end, you can probably get away with making it more shallow.
The false bottom should be deeper if you are growing a cactus or succulent. I recommend throwing in another one or two inches just to be safe. Cacti and succulents are very sensitive to overwatering. So allowing for more space in the drainage layer is going to allow more water to drain out of the soil.
However, there is a case that can be made for not making your drainage layer too deep. If your drainage layer is really deep, that’s going to detract from the amount of water that evaporates and condenses above the substrate where your plants are. More of that water is going to be cycling in the drainage layer itself the deeper it goes.
When this happens, your plants may not be getting enough water and humidity, meaning you’ll have to add more water into your terrarium to compensate. The net effect of doing this is that there’s going to be more stagnant water in your false bottom, which can lead to mold growth.
The reason this doesn’t happen in a succulent terrarium or an open terrarium is that your plants won’t need much water to begin with, so there’s no need to add any more water than is necessary. A deep drainage layer in this case will provide increased drainage with minimal buildup of stagnant water.
What is the best terrarium false bottom mesh?
On top of your false bottom, you should look to add some kind of separation material. The purpose of the separation material is to prevent your substrate from falling into the drainage layer while still allowing water to pass through. It’s also going to stop any plant roots from reaching into the drainage layer and developing rot.
In terms of shape and size, you’re going to want to get something that’s relatively flexible or moldable and has small openings for water to pass through. It’s going to make your life a lot easier if your material is flexible because you can cut and shape it to the exact dimensions of your terrarium. Flexibility also allows you to curve the edges upward as an additional barrier stopping plant roots from growing into the drains layer.
Here’s a short table listing some possibilities I’ve considered for separation materials:
| Material | Cost / sq ft | Min bulk price | Pros | Cons | Source |
|---|---|---|---|---|---|
| Aluminum window screen | $0.37 | $8 / 21 sq ft roll | -Cheap -Easily cut -No hole poking required -Surprisingly sturdy -Tough -Discrete / not very visible | -Rust resistant, but not 100% guaranteed -Edges might be sharp when cut | Home Depot |
| Charcoal fiberglass window screen | $0.36 | $10 / 28 sq ft roll | -Cheap -Easily cut -No hole poking required -More rust resistant than metal -Somewhat sturdy -Tough -Discrete / not very visible -Makes you feel like a pro terrarium builder | None I can think of | Home Depot |
| Saran wrap | $0.03 | $6 / 200 sq ft | -As cheap as you can get | -Flimsy -May tear easily -Can be annoying to work with -Risk of substrate ripping it due to weight and falling in -Need to poke your own holes -Water doesn't pass through as easily | Amazon |
| Sphagnum moss | $1.56 | $5 / 4 qt bag (~3.2 sq ft) | -All natural -Purifies water and air | -Not the cheapest option | Amazon |
| Grocery store plastic bag | $0.03 | $0.10 / bag (~3 sq ft) | -As cheap as you can get -You probably have one at home already -Easy to cut and shape | -Flimsy -May tear easily -Need to poke your own holes -Water doesn't pass through as easily -May not be aesthetically pleasing | Your state's plastic bag laws |
| Weed blocker | $0.60 | $9 / 15 sq foot roll | -Retains shape well -Does not tear easily -Easy to cut -Can use leftovers for your backyard -Discrete / not easily visible | -Water doesn't pass through easily | Home Depot |
Synthetic wire mesh will probably work best. I like that you don’t have to poke your own holes and it’s flexible, but retains its shape pretty well at the same time. All you have to do is just buy one roll and you’ll be set for life. Just make sure to pick one that has relatively small openings, not something that’s more like a net. Window screen mesh is what I usually have in mind.
If you’re on a really tight budget, my recommendation is to use some kind of plastic trash that you have lying around. The first thing that comes in mind is any grocery store plastic bags you have saved up.
Plastic bags might not have all of the benefits of a synthetic wire mesh, but it performs its function just fine. In fact, that’s what I used for my first terrarium (which is still doing fine by the way).
To use a plastic bag, you just need to cut out a shape slightly larger than the size of your container, poke some holes in it, and place it on top of your false bottom. That’s pretty much it.
False bottoms for opened vs. closed terrariums
The guidelines I listed above should be applicable to both opened and closed terrariums. Both styles of terrariums will benefit from having a false bottom installed, and the pros and cons of which material you use will be the same for both styles of terrariums.
The only distinction I would make between the two is that opened terrariums could benefit from a deeper false bottom. This is because the type of plants that grow in open terrariums tend to prefer dryer, more arid conditions. A deeper false bottom will allow for greater drainage capabilities in the terrarium which is very beneficial for water sensitive plants.
If you’re looking for exact numbers, I would say for an open terrarium you can aim for about 2-3 in for your false bottom, while a closed terrarium may be fine with about 1-2 in.
Can I have a terrarium without a false bottom?
In certain cases, you may be able to get away with not having a false bottom in a closed terrarium. If you are only growing moss in your closed terrarium, you shouldn’t need a drainage layer since moss doesn’t have any roots. In that case, a false bottom wouldn’t really provide much benefit since moss doesn’t depend so much on the quality of the substrate layer.
If you’re wondering if your particular situation will be fine without a false bottom, I would say it largely depends on what you’re trying to grow in your terrarium. If any of your plants have roots, they will benefit from having a false bottom in your terrarium because of its beneficial effects on the substrate layer.
Check out this article if you want more details about growing moss.
How to properly water your terrarium
This topic probably deserves its own blog post, but I’ll quickly give a summary here for your reference.
When it comes to watering your terrarium, there’s a fine balance between over and underwatering your terrarium. Too little, and your plants start going yellow and getting crispy leaves. Too much, and your terrarium turns into a fogged up swamp in a bottle with a lot of rot and mold. Yuck!
Anyone new to caring for terrariums might start to feel worried when their terrarium hasn’t been watered in weeks or months. This can lead them to add more water to their terrarium when it isn’t necessary. It’s just that need to do something to make the terrarium “healthy”.
If you feel this way, let me reassure you that your terrarium is going to need much less watering than a traditional houseplant. In a closed terrarium, water recycles itself within the container rather than evaporating into the air as happens with a typical houseplant or garden plant. This means that the water levels sustain themselves over a long period of time without any need for a top off.
There’s a few signs you can look for to determine when you have a perfect balance of water in your terrarium:
- The substrate feels moist, but not soggy
- There’s only a little bit of condensation just at certain times of the day (morning and evenings)
- Your plants look green and healthy
- The drainage layer doesn’t have much stagnant water
- There’s no mold growth in your terrarium
Every so often, it may be worthwhile just to touch the substrate and observe the condensation levels throughout the day to monitor your terrarium’s water levels. If your terrarium checks off all of those boxes above, it’s probably doing just fine in terms of the water levels.
If you notice that your terrarium does need a little water, the preferred method of delivering it to that water is through a misting bottle. While you could try pouring water from a cup, there’s a greater risk of generating local areas of over-watering which might lead to a little bit of mold or rot. It’s really hard to evenly distribute the water when it’s being poured from a cup.
If your terrarium has a little bit too much water, all you have to do is open it up and let the water evaporate on its own for a few hours or even a day or two. You can also wipe off any excess condensation that you see to remove water from the system manually.
In terms of which water you should use to water your terrarium, preferably you should use distilled or rain water. Tap water might be okay, but there are trace levels of chlorine, lead, and salts in there that might not be so great for your plants.
Tap water might also lead to mineral buildup on your container walls over time. As water condenses and evaporates within your container, any minerals or salts will deposit on the container walls which can cause your container to look cloudy. You can always wipe it off if you notice it’s building up too much, but it’s just another thing to think about.
How problematic tap water will be for your particular terrarium largely depends on your area’s tap water quality. However, most likely you probably won’t run into problems if you have to use tap water. I’ve used tap water myself and haven’t had too many issues because of that so far in my terrariums.
Will the false bottom affect the pH levels?
I mentioned pH levels in one of my bullet points in the table up there. In case you didn’t know, pH is a measure of how acidic or basic water is. Lower pH numbers mean that the water is slightly acidic, while higher pH numbers mean it’s more basic. A pH of 7 is neutral, smack dab in the middle.
When it comes to growing plants, most plants will prefer slightly acidic water in the range of 6 to 7 pH. That includes moss and ferns, probably the most common plants you might see in a terrarium.
The false bottom will not significantly affect the pH levels. Most likely, no material you put in there is going to significantly shift the pH to dangerous levels, unless you’re throwing some kind of alkaline salt in there (not something you do by accident).
In my opinion, you don’t need to go in and measure the pH levels. Most likely this is already fine for your terrarium and there’s no need to measure it or do anything to adjust it. It’s mainly a thing to look at for people who are either very paranoid or who want to hyper-optimize their terrarium, which isn’t entirely necessary to be successful.
So that’s pretty much it for what you need to know about false bottoms. If there’s anything I missed, feel free to leave a question in the comments below and I’ll see if I can respond. Other than that, thanks for reading and feel free to check out any of the related articles below to learn more about terrariums.