Lobelia cardinalis is a light green stem plant that has attractive salad-like leaves. While the leaves can be purple when grown emersed, the submerged leaves are generally totally light green, with the slightest hint of purple under very high light. It originates from America and grows in moist soil along river banks and the sides of ponds. The round leaf "mini' cultivar is gaining popularity as it has rounder leaves that serves as a good contrast to many plants. It is therefore it is very popular in Dutch style planted tank layouts where contrast between leaf shapes and colors is important.
It takes pruning well and grows at a slower rate compared to most stem plants. This makes it a very easy bush to control and shape. Its ability to form neat, dense bushes makes it ideal for foreground and midground placement even though it is a stem plant.
Higher light levels give it a more compact growth form, even though it can grow well in medium or even lower light levels. It benefits well from CO2 injection. In low tech tanks, it tends to have deteriorating older growth and less compact forms. Due to its slower growth rates, it is a plant that favors stable tank conditions. In high light levels, its older leaves are prone to spot algae if conditions are unstable or if organic waste levels are not controlled.
Lobelia cardinalis have a hint of purple in their submerged leaves under high light. It is only their emersed leaves that can look very purple.
Key success factors
Stable and clean tank environment helps a lot against algae issues
Higher light levels (80 umols of PAR) give more compact and bushy growth
Regular fertilization required to maintain lush green leaf tones
Carbon dioxide injection greatly improves plant health
Pruning and propagation
Lobelia cardinalis is actually a stem plant that branches readily, so it can be pruned similarly to other stem plants; just cut above an internode. The cut off head can be replanted into substrate to generate another plant. The remaining rooted portion of the plant regenerates new shoots easily, growing more bushy over time.
This plant is able to take repeating trimming well, so for most tanks it can take months of trimming without needing to be replanted. However, if the bottom part of the stem becomes badly deteriorated with smaller and smaller leaves being produced from the base, it is a sign that the plant needs to be topped and replanted.