Aquatic plants: which substrate to choose?

When the first tarp ponds were created, the choice of substrate was often the same: a mixture of peat, clay, soil and sometimes sand. Minerals or fertilizers were often added to these mixtures. The negative point in the choice of these materials was, however, that the nutrients passed directly into the water. As a result, the plants no longer absorbed them. Substrate selection for aquatic plants is therefore more technical than it seems. Here are all our tips for making a good choice.

Choice of substrate for aquatic plants

Keep in mind that the water quality in your pond will depend on the type of substrate used. Therefore, it is preferable to choose a substrate for plants. Gravel or sand without lime is fine. It should also be known that peat added to the substrate would cause the formation of methane in the water. However, this gas would then prevent the penetration of air and thereby reduce the activity of bacteria necessary for aquatic plants.

aquatic plant substrate water lily
Credit: iStock

Soil quality for “special aquatic plants”.

There are ready-made potting soils for aquatic plants, but they often contain peat, which, as we have already explained to you, is not recommended. However, you can improve it by adding sand, for example. This will indeed increase the permeability of the soil and thus the growth of bacteria. You can also add a 10 cm layer of gravel to this mixture. This will help to prevent the peat from rising.

Choice of fertilizer and water

Adding fertilizer is not necessary, because all the nutrients that plants need are already present in the substrate. When the pool is full, dead leaves, grubs and some decaying plants will settle there. They will then represent natural fertilizers.

Finally, keep in mind that the quality of the water is also chosen. Indeed, it is necessary to avoid tap water and opt for rainwater. A collector can be used for sufficient supplies.