Practical Use of Garden Soil as a Rich Plant Substrate

By Nimish Mathur
Nimish was brought up in India, but now resides in the U.K.
Original to Aquarticles

In many countries the availability of a rich aquarium substrate is a problem. Whatever products are available are too expensive or are inappropriate. I have experimented with garden soils and its mixtures to get exceptionally good results in a budgeted manner and with easy availability.

The contents of the entire substrate used are as below:
- Lava rock based gravel
- An appropriate heating cable
- Sterilized garden loam soil or standard clay
- Vermiculite or Perlite or a similar high CEC soil additive
- Plain silica sand
- Small grain aquarium gravel (2-3mm)
- Peat moss

Preparation of the mixture:
- Take an appropriate volume of soil. Say your tank is 90cm x 30cm, and you want a 1" layer of soil, you need about 90cm. x 30cm. x 2.5cm. (1" = 2.5cm) = 6750ml., or approximately 6-7 litres of soil. This measurement can be done in a measuring bucket.

- Vermiculite is basically fired mica. When raw mica is heated in a furnace it loses water, and this loss, in the form of small explosions of steam, expands the mica like popcorn. This gives Vermiculite a very porous structure and a very good CEC (Cation Exchange Capacity is the ability of the medium to absorb cation ions, (minerals from fertilizers), and hold them making them accessible to the plants when the plants need them), but unfortunately it also becomes lighter than water. This is one of the reasons it cannot be used directly as aquarium gravel. The Vermiculite has to be mashed between your palms so it can be easily mixed in with the soil.
For the above mentioned tank, take about ½ litre of Vermiculite and then mash this after moistening it with water. The palms of your hand will be covered with gold dust from the mica in this process.
Perlite is easier to mash when moist but is not easily available and is much lighter then Vermiculite.
If  your are using a clay instead of loam soil, then it is possible to skip this additive as clay itself has a very high CEC.

- The next step is to make the soil less compact. This is done by mixing an appropriate amount of regular river sand or silica sand into the soil. I mix around 2kg. of sand for the above setup, but this may vary depending on the clay or loam you use. The purpose is that the soil does not get too compact and remains a little porous. The quantity is not that critical but some soils already have some sand pre-mixed. Do not use beach sand or any type of sea sand as it contains many chemicals that may harm the plants.

- Add about 1 handful of peat moss to this soil. The purpose of peat moss is to add some organic matter to the substrate to provide a kick-start mechanism. In a freshly set up aquarium there is no organic matter, so the plants cannot get all the required nutrients right away. In an established tank however, things are different as the substrate accumulates enough organic matter to keep the plants going. Peat can help the plants kick in straight away.

- Add about 10 ml. of your regular aquarium plant fertilizer to this, and mix the entire setup thoroughly.

When you cannot see any visible Vermiculite or sand, the mixture is well mixed. Keep this aside for later use.

Setting up:
Now let's get back to the tank again:

- Lay the heating cable on the glass base as per directions, and cover it with a 1" layer of lava rock based porous gravel. Pull the loose heating cable strings so they rest above this 1" gravel layer rather than under it. The purpose of this layer is to provide some space for water flow beneath the soil layer. If the heater is all covered by compact soil, then water flow due to thermal differences will be reduced.

- Distribute the prepared soil mix over this layer to a depth of 1½ ". This will further compact by the weight of sand and water to form a 1" layer.

- Evenly distribute the soil and slowly pour the sand over it. It is better to use dry sand rather than wet, as dry sand will spread more evenly. Make a 2" layer of sand over the soil, and top it up finally with the gravel.
This 2" layer of sand will prevent anything from the bottom layer to come up. The layer of gravel, being larger than the sand grains, will remain above the sand to protect it further.

- The substrate is now ready and you can start slowly pouring water over the sand to a depth of 5" - 6".

Planting:
When planting the plants, plant them above the soil level. A 2½" layer of sand will be enough to hold any plants down. Since the roots will be close to the soil layer, they will start getting nutrients from there almost immediately.
The heating cable will help circulate oxygen and nutrients to the roots.
When fully established, keep things like iron under control. If it peaks, perform a water change until it stabilizes.
It is best to have some fast growers initially to consume the excess nutrient flow. With moderate lighting and a little CO2, the entire tank should stabilize within two weeks. During these two weeks you will also experience a spurt in plant growth. If you start to get little dust algae don't worry, but turn off the lights for a two hour period of darkness in the afternoon. This will get rid of algae for now.

I have used this setup on low light and high light tanks, without adding CO2 in low light and adding CO2 in high light, with enormous success.

I hope this article helps aquarists who have wanted to keep rich planted tanks but have not been able to do so.