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How To Turn A Fish Tank Into A Garden: Step By Step Guide

If you have green fingers and a very limited outdoor space for a garden, it can be hard to indulge yourself. However, there is an easy workaround.

You can turn an old fish tank lying around your house into an indoor garden. Scratch that you can buy one from a nearby garage sale for this purpose.

A fish tank garden (also called a terrarium) looks absolutely beautiful. What’s more, it is space-saving easy to create, nurture, and maintain. Even your kids can have fun making one with a little guidance from you.


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How Do Fish Tank Terrariums Work? 

Depending on the kind of plants grown inside, fish tank terrariums can be sealed or open.

Sealed fish tank terrariums (equipped with a removable lid) are self-nourishing and require little maintenance.

Water released from transpiration by plants settles on the walls and cover of the tank and trickles back into the soil.

Similarly, heat generated by the incoming sunlight remains trapped inside the glass.

It is more or less a miniature greenhouse in principle.


Source | Wikimedia Commons

What Kind of Plants Can You Grow In A Fish Tank Garden?

Here are some plant groups that you can grow:

Desert terrarium for growing plants like succulents and cacti (open terrarium).

Herb terrarium for growing herbs like thyme, oregano, rosemary, and basil (open terrarium).

Bog terrarium for carnivorous plants like sundew, venus flytraps, and pitcher plants (open terrarium).

Rainforest or woodland terrarium with moss, ferns, and violets (sealed terrarium).


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What Materials Do You Need?

Although you cannot create a full-size garden in a fish tank, you can design it to resemble a miniature replica.

Apart from being a convenient way to flex your green fingers, fish tank gardens can also serve as a decorative piece to liven up your space.

The materials you need include:

  • An old fish tank
  • Detergent
  • Potting mix
  • Gravel
  • Your preferred seeds, seedlings, or young plants
  • Decorative pieces
  • Spray bottle for watering the plants

How To Prepare A Fish Tank Garden?

Step 1 – Clean the Fish Tank


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To start with, you need to ensure your tank is clean and free from dirt or residue chemicals. If the tank has only basic stains and sort, you can use regular dishwashing detergent and hot water to scrub it out.

However, if the glass tank has tough, old, dried-out stains or crusts, the cleaning process may be a bit more intense. It may also require the use of specialized cleaning products.

Rinse thoroughly to make sure you get rid of all the cleaning agents.

If you want to avoid using chemicals, you can also wipe down the tank with vinegar and rinse thoroughly. After rinsing, you can leave the tank out to completely dry out before adding your potting soil.

Also, make sure to check for any cracks in the glass. If the crack is on the top half, the tank is still usable as it won’t leak water and nutrients out of the soil.

However, if it is at the bottom, you can either discard it or, if you like, dabble in DIY crafts, reseal the crack.

Step 2 – Add Gravel


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Once your tank is clean and ready for use, you can create the garden bed. Depending on how deep the tank is, you need about 1-3 inches of gravel to line the entire bottom.

Adding gravel or pebbles as the garden bed base ensures that your plants have proper drainage. Normally, you wouldn’t have to worry about this while planting outdoors. However, since the fish tank does not have drainage holes, you need to ensure your plants do not become waterlogged.

If you prefer to save costs, you can always pick up pebbles from outside instead of buying gravel. First, however, be sure to soak them up in boiling water for a few minutes to reduce the population of any bacteria lurking on the surface.

You must be wondering if the soil outside already carries bacteria; what’s the fuss all about?

However, bacteria in an enclosed container without proper drainage could quickly multiply and damage your plants.

After lining the bottom of the tank with either gravel or pebbles, sprinkle a layer of activated charcoal over it (about the height of one fingernail). Activated charcoal is highly absorbent and can absorb moisture and vapors many times its weight. This keeps the roots of your plant safe and prevents the accumulation of humidity and gas.

Without that additional insurance, the humidity level inside the tank builds up, which then creates a favorable environment for root-rotting bacteria to thrive.

Activated charcoal is more important if you’re doing a sealed fish tank garden.

However, if you’re creating an open fish tank garden and using plants that thrive in high humidity (e.g., tropical plants), you may omit to add charcoal.

Step 3 – Add Quality Potting Soil 


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After creating the gravel base for water drainage, get quality potting soil that works for the plants you want to grow. You can either buy one or make the potting soil yourself.

Add at least 6 inches of potting soil over the gravel bed to guarantee your plants a decent vertical root development. Note that potting soil is quite different from regular gardening soil, and if you want your plants to grow well, you cannot use them interchangeably.

If you notice that your potting soil is heavy, you can mix it with perlite to loosen it up and improve aeration.

Since a fish tank can be quite large and heavy, be sure that you’ve set it up in its permanent resting spot before pouring in the soil, or you won’t be able to move it.

Step 4 – Choose Your Preferred Plants 

Settle on the kind of garden you want to create using the fish tank.

Choose compatible plants that require the same growing conditions and humidity levels to grow well.

The best starters for fish tank gardens are seedlings and small plants, as they have the highest survival rates.

Also, if you’re big on aesthetics, you can arrange the plants before planting to see how they’ll look once they go into the terrarium.

One visually appealing arrangement is to place the smaller plants in the front and the taller plants at the back. This arrangement also ensures that the shorter plants catch any available light and grow well.

Another arrangement is to place the taller plants in the middle and surround them with the shorter ones. This improves the aesthetics of the terrarium and ensures that every plant receives an adequate amount of light.

Step 5 – Begin Planting


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After mapping out where the plants go in the terrarium, it’s finally time to plant. Use your fingers or a long teaspoon to make holes deep enough to accommodate the roots of your seedlings or young plants.

Place the plants in the holes, one at a time, and pat the potting mix around the hole to lightly cover it up. Repeat this process until the terrarium is full or you’ve planted all the seedlings. Leave at least 4 inches of space between each seedling as you plant.

For herbs, it’s best to grow them from seeds as it is easier to manage, and you don’t have to struggle for space for other grown plants.

Plant the seeds just as you would the seedlings of other plants. However, place about 2-3 seeds in one hole before covering as not every seed germinates.

A fish tank garden is a great way to grow plants that would otherwise have been difficult to manage outside, e.g., carnivorous plants and ferns.

Step 6 – Add Your Decorative Pieces 

Once you’re done planting, you can finish your new fish tank garden by adding any decorative pieces you like. However, keep things as natural as possible. Colorful rocks, stones, figurines, and driftwood are great pieces to add.

Some people may prefer to keep their decorations minimalistic and add only identification plaques or similar items.

How to Care For Your Fish Tank Garden?

For your indoor garden to thrive, you have to give it constant care and maintenance. This is perhaps the most challenging part of owning a terrarium. Unlike outside gardens, where you only have to tend occasionally, you need to pay close attention to your indoor plants all the time.

1. Sunlight


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The first rule for maintenance is the location of the fish tank garden. You have to place it in front of a large window where it has access to adequate sunlight. Many herbs, particularly basil, require exposure to full sunlight to grow well.

Don’t place the terrarium under direct sunlight, or the glass will magnify the heat and dry out your plants.

2. Water


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Keep a small spray bottle filled with water near the tank to mist the plants as required. A spray bottle with a long, tiny neck does an excellent job. That way, you can reach in and mist the soil directly rather than the leaves.

Remember to dampen the soil without over moistening it. Excess water in the fish tank has nowhere to run off, so it’s best to keep the moisture inside to a minimum.

A makeshift gauge can also be useful to check water levels in the soil before watering. Get one of those wooden sticks that you’d use for a bbq and stick it into the soil (watch out for the roots). Take the stick out and use your fingers to check the moisture level in the soil. If the stick is super wet, you can forego watering the plants.

Another trick to prevent overwatering is to check if water is dripping into the gravel or pebble base. That’s a good indicator that the soil has become very saturated.

If the terrarium is sealed, open the lid occasionally to air and dry it out, especially if you notice moisture on the walls.

3. Fertilizer

You can choose to fertilize your plants to give them additional nutrients. However, try to use lower quantities than those suggested on the package label.

If you overfertilize your plants, they may perish due to nutrient burn. Also, overfertilization can induce rapid growth, which your terrarium might not be able to sustain.

Lastly, emerging plants are likely to be overshadowed and starved for moisture and sunlight.

4. Cleaning The Tank

Although it does not have direct importance to the growth of the plants, you should still clean the body of the tank.

If not for anything else but hygiene and aesthetics.

Regular chemical-based cleaning products are very alkaline. Therefore, if they accidentally leak into the soil, they can alter its pH and cause damage in the long run.

Instead, consider non-conventional cleaning methods like wiping down the tank walls with soft paper or rag and a very diluted vinegar solution.

5. Weed, Pests, and Diseases


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Check your terrarium regularly for signs of pests.

Also, check out and prune brown or yellow leaves from plants in the tank, as this is a sign of a possible underlying disease. Removing them prevents the outspread of the disease to other plants.

If you’re growing ferns in your terrarium, trim the leaves regularly to prevent them from overgrowing.

Pests To Look Out For In Your Terrarium


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Some micro-fauna may be beneficial to the self-sufficiency of your fish tank garden, e.g., springtails and isopods, as they break down decaying organic matter and feed on other harmful fauna.

However, some other insects and animals are completely unsuitable for life in a fish tank garden, or they’ll ruin all your hard work. Examples of these pests include snails, slugs, beetles, ladybugs, ants, spiders, gnats, mites, and mealybugs.

Some of these pests find their way into the tank via the substrate used as soil and the plants themselves.

These pests might impact your terrarium in multiple ways. While some pests are likely to be harmless (only being annoying and unsightly to see), others might wreak havoc on the plants (mealybugs, gnats, and mites are particularly guilty of this).

Finding a lasting solution to pest problems in the tank garden can be challenging. Depending on the gravity of infestation, the interventions could range from just quarantining affected plants to completely changing the soil.

Final Thoughts

Turning a fish tank into a garden is a very fun personal project that you can undergo, especially if you’re trying your hands out at gardening but without the usual backbreaking labor.

While you may not get enough produce to sell at the market (or any at all), you’ll always have enough for your immediate home use.

The aesthetic uplift that the fish tank garden will give to your space is also a bonus.

How To Turn A Fish Tank Into A Garden: Step By Step Guide

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