5 Easy Steps To Turn Your Old Fish Tank In A Stunning Garden


In today’s world, too often we let valuable items go to the landfill that could easily be repurposed and restored to their previous greatness. One thing that many of us have laying around the house or in storage is an old fish tank or aquarium. Hence, why not use it as a small glass garden!

Growing plants in a glass container is an ideal and beautiful way to repurpose a used aquarium as the closed environment creates conditions in which many herbs can thrive (and make you look great with your friends!).

Hence, how do you turn an old fish tank in an indoor garden? To create a fish tank garden you need to follow 5 simple steps:

  1. Prepare the aquarium
  2. Add pebbles-gravel and charcoal
  3. Prepare the soil
  4. Choose the plants to growth
  5. Start planting

Gardens can be grown in a large variety of containers and utilizing an old fish tank is an excellent and green way to do it. Let’s dive-in in the detail to do so with some extra information on how to maintain in the long term such a unique garden in a way to be long term envy for your friends and a spectacle for your eyes.

Designing a Fish Tank Garden

Having a small garden in your home is a great way to get fresh produce all year long. Though you clearly cannot create a full-size garden in a traditional aquarium, you can design a mini version of it, easy to maintain, to produce some edible herbs your favorite pasta plate (someone said basil!). Plus, you will be using materials that are easy to come by or you may already own, lowering your wastes. 

All you need for this project are only the following key items:

  • An Old Fish Tank or Aquarium 
  • Liquid Dish Detergent
  • Gravel or Pebbles
  • Potting Mix
  • Activated Charcoal 
  • Small Plants, Herbs, or Seeds 
  • A Spray Bottle for Watering
  • Decorative Items 

Step 1 – Prepare the Aquarium 

To start, you want to prepare your aquarium for planting, ensuring that it is as clean as possible before adding your plants. This is a fairly easy process, especially if the fish tank has simply been stored in your home. Most use a basic liquid dish detergent and hot water to scrub the tank out. Some also suggest vinegar as a better disinfectant if you do not want to use soap. You will want to wipe down the aquarium with a clean, soft cloth and rinse it out fully. Once the tank is rinsed out thoroughly, you will want to dry it well before placing any soil.

The cleaning process might be intense in case of an old crust deposited on the glass as can it can be as hard as a rock to remove. This implies lots of hard work and use of specialized products such as the Bar Keepers Friend (a quite famous cleaning product, that can also be used for tanks is a Cookwear Cleanser here on Amazon) is recommended. If this is your case you can find an interesting video at the end of this post.

Washing it is also a way to check if presents any crack that you might not see with your eyes. Just place a bit of water and see if it is leaking. If the crack(s) is on the upper part, it is not a problem as the soil will not fill the whole tank. If the crack is at the very bottom it can still be solved if you like the challenge of a DIY. In this case, check the youtube video at the end of this post. If all OK, let’s go to the next step.

Step 2 – Add Pebbles-Gravel and Charcoal

Once your fish tank is ready to begin the planting process, you will want to find gravel or pebble. You will spread one to three inches of this gravel into the bottom of the aquarium, depending on the overall depth of the container. This gravel is added to offer a way for the plants to have proper drainage as your water tank does not have drainage holes. You will want to ensure that whatever gravel or pebble type you use covers the entire bottom of the fish tank. 

Pebble are a must at the bottom of your fish thank

Tip: if you want to save money, you can always use pebbles that you find in any outdoor garden. In such a case, just for extra care, I will place them in boiling water for a couple of minutes and let them dry. This is because outdoor gardens are way more rich in bacteria life that, in a container without drainage, might develop way too much, harming for your herbs. The boiling process will kill the majority reducing dramatically such risks.

Once you have your gravel smoothed out across the bottom, you will want to sprinkle a layer of activated charcoal over the top of around 1 fingernail in height. Indeed, given the enclosed nature of your glass garden, the herbs might suffer for the accumulation of gas and humidity.

Activated charcoal (here quite a good one on Amazon, that can also be used for other purposes) is a fantastic material that has the capability to absorb many times its weight in water keeping your plant roots safe. Indeed, without it, the humidity will build up in a container without drainage holes (as your fish tank) stimulating the growth of root-rotting bacteria. 

However, I need to highlight that after a few discussion with some gardener, among them our friend Ruell Smith that turn is an old tank in a beautiful garden, highlighted that he did not need charcoal. However, this because is using plants that strive in humidity and also because he is using a smart technique for watering them (more on this later).

Step 3 – Quality Potting Soil 

At this point, you can either create your potting soil (that’s lots of fun and learning, for more check out this article). If you already have enough with your DIY fish tank transformation then you can buy one of the good potting soil available.

If you want a suggestion, here an article regarding my favorite potting soil, the best compromise between quality and price. If you are in a hurry you can pick up the Foxfarm (here on Amazon), one of my best pick. Soil should be added until it is about five or six inches from the top of the tank or at least 6 inches of soil in order to guarantee a decent vertical root development.

Tip: a fish tank can be quite large. Hence, even if not filled with soil can get really heavy. I do recommend to place the soil when the tank is already in its final location. Indeed, if it gets several kgs in weight might be difficult (and dangerous) to move it.

Step 4 – Choose the Plants 

If you want to ensure your plant’s survival, you will want to purchase seedlings or small plants. You should arrange the plants before planting to ensure they fit the way you would like and are visually appealing. 

Tip 1: you should place the taller plants in the back of the aquarium and smaller plants in the front, allowing them to catch the most of the available light.

Tip 2: For those who want the aquarium to be visually appealing from all angles, you may want to place the taller plants in the middle and surround them by smaller plants (if you have already plants to put in straight away). This will not only create a great visual effect but also will guarantee that all your herbs (or plants, this guide apply in general) receive a sufficient amount of light.

Step 5 – Begin Planting

You will want to plant the seedlings or plants one at a time, using your fingers or a small utensil (a long teaspoon or the long neck icecream ones for instance) to make a hole for the roots in the soil. You will want to place the plant into the hole and then pat the potting mixture (here for the best potting mix around and how to create your own potting mix) around them lightly to cover. You will want to repeat the planting process until all of the seedlings are in the soil, with a distance of approximately 4 inches (even 3 is fine, but I would not go lower than that). 

I will place 1-2 seeds per hole (as not all seedling growth) as not each seed will bloom.

Growing herbs from seeds for a fish tank is an easy option as you do not have to fight with space in placing already developed plant in the tank

Once the plants are in the soil, you can finish off your garden by adding any decorative features you want. It is best to keep your decorations as natural as possible, like driftwood, rocks, stones, or even figurines. However, some keep their gardens very minimalistic and only add plant identification plaques or similar. This is important as it will reduce the maintenance process.

Caring for Your Indoor Garden 

Once your seeds (or small plants) are safely placed in your fish tank and ready to grow, this is where the challenge starts. Maintaining the herbs at their best during their growth is the real challenge. However, tank design and location can be of significant help.

Most homeowners who create a fish tank garden keep a small spray bottle of water nearby to mist the plants with as needed. If possible have those with a long tiny neck so to mist the soil rather than the leaves. Indeed, if you can, always try not to water the leaves directly. In general leaves are not designed to keep up water.  You will want to use a fine mist that provides enough water to dampen the soil without overwetting it. You will want to place the tank in front of a large window to receive full of sunlight, important for many herbs like basil for instance. 

Tip: here the humidity is important. Indeed, your tank does not have drainage holes and only the activated charcoal and pebbles are helping with drainage. Hence, I would consider having always on the side of the tank a wooden stick (as those that you might use for bbq) to use before watering. This will be your best gardening friend. Indeed, you can stick it into the soil (without damaging the roots) and check the moisture level of the soil by touching it with your fingers. If the stick comes out wet then it is not the right time to moisturize. The very first days will be a trial and error process. However, over time you will get used to.

Which Herbs to Grow? 

This fish tank project is suitable for any herb (and plant). Indeed, although in a container without drainage holes, if you follow the tips given above, growing your favorite herbs should not be difficult. Moreover, you will leave open (at the top) your fish tank. If you close it, you convert it in a kind of terrarium, way more challenging to maintain due to the high air humidity of this environment, that will build up and unsuitable for many herbs.

When you have your indoor garden you can get fresh ingredients all year round! If you are hoping to add both beautiful and edible plants to your garden-aquarium, some great herbs are: 

  • Basil
  • Chives
  • Mint
  • Oregano
  • Parsley 
  • Rosemary
  • Thyme 
  • …and many more

Regarding the herbs to plant I do suggest to make sure that they have similar water requirements as they will share the same soil. In other words, I would not place rosemary and basil in the same tank. This because the former requires drier and more drained soil than basil does. 

Another warning is for mint. I would either think to grow only mint or place some kind of barrier in the soil to avoid its roots to spread. Indeed, mint is a very invasive species. A few examples of great herb companion are:

Mint is a very invasive species, hence I would avoid in a tank in which you want also other herbs
  • Basil and Cilantro;
  • Thyme and Sage;
  • Chives with most of the herbs excluded rosemary;
  • Different type of basil (like Thai basil and Genovese basil);
  • Oregano and Basil;

Practical Case Of Study: A Chat With Ruell Smith

On my spare time, I was reading some Facebook posts on herbs in one of the countless group I subscribed to (a great way to learn, by the way) where I had the opportunity to have a quick chat with Ruell Smith. He shared with me how he created his own fish-tank garden (flourishing after 5 months) plus some tips I am sure will make your life easier.

The fish-tank garden of our friend Ruell (you can follow him on Instagram at plant_daddie)

Ruell is not focusing on herbs, however, the lessons you can learn might be valuable so I decided to include them in this article.

Starting from the bottom of the fish tank as you can see from the above photo we have a 4 inches of clay rocks. He is using a garden potting mix to which he added perlite. This is a good solution if you notice that your potting soil is too heavy.

He is not using charcoal and his tank is flourishing! This is because of 2 reasons: 1) he wisely chosen plants that withstand humidity pretty well 2) the tank is open. If you decide to close the tank (I do not recommend) the close “terrarium” environment might get really humid, and the charcoal in such a case is a must.

Tip: to avoid overwatering (that can ruin your fish-tank) Ruell is using a very smart technique. He stops watering the plant when he notices that the water start dripping down to the rock layer. This indeed means that the soil is moist enough.

He fertilizes his plants, but with an amount of fertilizer lower than the one suggested by the manufacturer. This is again a wise choice as he avoids all risk of burning the plants due to the excess nutrients, especially if you are starting.

Tip: he chosen plants with the same level of watering requirements. Indeed, as I also mentioned earlier, this is important if you want to avoid your herbs to suffer.

Tip: the beauty of a fish-tank garden is given by the possibility to watch, through the glass, your herbs growing. Hence, having a clean tank is key.

You need some “out of the box” solutions to keep your fish-tank clean without damaging the plants

Ruell is not using any chemical product for cleaning the wall of his tank. Indeed, the majority of such products are very alkaline (pH very high) and, if they leak by accident in the soil, can cause severe damage to the plants. He is currently using screwed-up paper with a very watery vinegar solution.

Further Readings

If you are still unsure about the process or simply want to see some example fish tank gardens for yourself, there are several YouTube videos that go into visual detail that might help support more what stated here. Some great options are:

Andrea

A young Italian guy with a passion for growing edible herbs. After moving to the UK 6 years ago in a tiny flat, it was impossible to grow herbs outside. So I start my journey in growing indoor and so I decided to share my knowledge.

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