Liebig's law of the minimumIf plants just do not want to grow
The Law of the Minimum, made famous by the scientist Justus von Liebig (1803-1873), describes how plant growth is constrained by resource limitation. Plants need many different nutrients, the so-called essential nutrient elements, to grow healthy. If only one of these elements is lacking, plant growth will be inhibited, even if all other essential nutrients are available in abundance.
This is true for the other resources such as light and convenient temperatures, too. The scarcest resource thus restricts plant growth. This concept is referred to as the limiting factor.
Reference: Public Domain via Wikimedia.org
In relevant literature, Liebig’s law of the minimum is demonstrated by use of the so-called “Liebig’s barrel”: a barrel with differently high staves. Water runs into the barrel, but can only rise as high as the shortest stave permits, because it’ll leak from the corresponding gap. The staves represent the different nutrients and other growth factors, the shortest stave represents the limiting factor. The water level in the barrel symbolizes plant growth, which is limited by the respective minimum factor.
In relation to a planted tank or aquascape, this law clearly shows, how essential a complete nutrient supply actually is to ensure a healthy growth of your aquatic plants. We have covered the necessary resources in detail in our feature article on "Fertilizing a planted aquarium". These are essentially the four factors light, carbon (via CO2), micro- and macronutrients.
If aquatic plants show signs of deficiency, maybe even in combination with intensified growth of algae, the reason is usually an imbalance in nutritional support. According to Liebig’s law, one deficient factor might be enough to impair the healthy growth of your plants. So, giving them more light and CO2 will not result in better plant growth if there’s just a shortage of a specific nutrient like nitrogen or iron.
As a countermeasure, the nutritional gaps need to be identified and closed. For this, two things are important: First of all, the water parameters need to be checked using appropriate water tests and secondly, you should try to interpret the deficiency symptoms visible in the plants. The pattern of damage roughly helps assigning certain nutritional deficits. For this, we recommend the corresponding article on "Deficiency symptoms in aquatic plants".