When it comes to the subject of pond soil, opinions on the right substrate vary widely. While some pond owners manage completely without soil, others swear by ready-made products from the trade. But even these pond substrates differ greatly from one another. Yet it is not that difficult to make a solid pond substrate yourself.
Pond substrate is important for plants, fish and ultimately for water quality. Because plants cannot grow on the pond liner alone. Above all, however, a good substrate is essential for pond biology. It provides a food base and shelter for many creatures. And last but not least, the substrate is the colonization area for countless bacteria that ensure good water quality.
- gives support to the plants
- provides a habitat for bacteria
- binds nutrients
- protects the pond liner from harmful UV rays and injuries
When choosing a substrate, you should pay attention to different factors, because an unsuitable material not only leads to contamination in the water, but can also damage the pond liner. A good pond substrate should therefore have the following properties:
- low in nutrients
- low in pollutants
- smooth surface (in no case sharp-edged)
- larger pebbles can also easily damage the liner
- must not rot
- difficult to wash out
- must not float
Note: Do not use humus potting soil! Not only does it release large amounts of unwanted fertilizer into the water, causing algae blooms, but it may also form putrefactive gases as it rots
Unlike normal plants that grow on land, aquatic plants of any kind generally do not require humus-rich soil to thrive. They get their nutrients from the water that washes around the roots. However, these plants cannot do entirely without substrate. Various materials are generally suitable as pond substrate. Although they can also be used individually, in most cases a mixture of the different substrates is useful to achieve an ideal result.
Coarse pebbles can damage the pond liner. For this reason, they should only be used in the shore area for design purposes. Fine gravel, on the other hand, is quite a good plant substrate because it provides support for the roots of aquatic plants and does not release nutrients into the water. Although gravel itself cannot store nutrients from the water, over time the interstitial spaces fill with sediments that have sufficient amounts of nutrients.
Loam, loess or even silt binds the nutrients from the water particularly well and is therefore an excellent substrate for the aquatic plants in a garden pond. Even a small amount is sufficient for supplying nutrients to aquatic plants. Clay is also not easily washed away.
Bacteria can settle very well in sandy substrates. As a nutrient medium for the garden pond, sand is therefore ideally suited to stimulate plant growth and keep the water clean. In addition, mud does not collect between the individual grains, as is the case with gravel over time. Not only are beneficial bacteria present in this sludge, but pathogens and fungi that are detrimental to the health of the fish can also settle there. As a bottom substrate, especially for fish ponds, sand is therefore always the better alternative to keep the pond clean and the fish population healthy.
- fine-grained sand for ponds without fish population
- do not use sharp-edged sand (for example sandbox sand)
- river sand or aquarium sand is more suitable
- coarse-grained sand for fish ponds
lava granules or granulated clay
The porous material of lava rock or clay provides ideal conditions for bacterial growth, which plays a significant role in pond health. However, use only granules with a smooth surface, otherwise the film, roots of aquatic plants or even the fish could be injured.
Tip: All the above materials can also be used individually as pond substrate. Many pond owners have had good experiences with this.
Basically, the choice of the appropriate pond substrate depends on where it will be used in the pond.
Substrate on the pond bottom
The basis for a clear, healthy pond is primarily the substrate and bacteria. A good bottom substrate should have a large surface area. The microorganisms that provide clean and clear pond water need a substrate on which they can grow up. Particularly good are all substrates that are very porous and thus have a large internal surface area. This is because this provides ideal growth and living conditions for microorganisms. And these microorganisms are important for a stable biological balance. For this reason, you should line around 60 to 70 percent of the pond liner with this soil material.
- purely mineral
- must not have sharp edges
- gravel (river gravel such as Rhine gravel)
- Sand (river sand or aquarium sand)
- clay granules or lava granules in ball form (quite expensive for large ponds)
Pond soil for the plants
Swamp plants like the water lily do not thrive very well in a pure sand or gravel bed. They need an adapted substrate with storage capacity for nutrients and a loose structure to ensure good circulation in the water and high oxygen levels in the root zone.
Instructions for a solid pond soil
A pond soil for planting baskets is quite easy to make yourself. For a pond substrate that you can use for all types of plants, mix:
- 10 parts clay minerals (loam, loess).
- 10 parts sand or fine gravel
- 5 parts clay or lava granules
- 1 part rock flour
Tip: This pond substrate is not only lean and can store nutrients well, it can also be used to largely avoid fouling sludge
A solid pond substrate should be purely mineral and should in no case contain humus soil. Fine gravel, sand or porous clay granules are suitable for the substrate. If you want to use plants, it is best to use a mixture of these components with clay to better bind the nutrients.