Lobelia cardinalis, the cardinal flower, is a true American, a native plant originally found in the eastern and central regions of the United States on moist ground alongside rivulets, ponds and road ditches. Its emersed form sports green leaves with a purple underside and attractive scarlet bell-shaped flowers, which make it a very popular and beautiful ornamental plant in its land of origin. The submersed plant is of a light green, though. L. cardinalis has been used for Dutch-style aquaria for a long time, and is quite widely spread in trade.
L. cardinalis is an easy plant to care for. Lighting should be moderate at least, whereas higher wattage results in more compact, lusher growth. CO2 injection is not necessary, but still recommendable for strong healthy growth. Regular doses of liquid fertiliser are a means to determine the plant's overall size. A nitrate level of 10-20 mg/l and a phosphate level in the range of 1-2 mg/l as well as sufficient micronutrients and iron lead to fast, vital growth. Under these conditions, L. cardinalis will throw the most lateral shoots.
This uncommon stem plant only grows to the water surface at a moderate rate. It also tends to grow a large number of white roots on the nodes of its stems. This can be hidden if the plant is cut back carefully. Trimming is done by cutting off shoot tips, which can be re-planted. If you want to create a "plant street" with this Lobelia you ought to gradually shorten the intervals between trimming.
Its rather slow growth and well-controllable height makes L. cardinalis highly suitable for Dutch-style Leiden tanks, where it is frequently used for the creation of so-called streets. Its size and its unique leaf structure make it an excellent choice for hobbyists who want to create a rather formal layout.
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