Lobelia Cardinalis Care Guide – Planting, Growing, and Propagation

Lobelia Cardinalis (cardinal flower) Care Guide – Planting, Growing, and Propagation - Submerged form

Lobelia cardinalis is a fascinating green stem plant characterized by lovely oval leaves when grown submerged or intense red flowers when grown emersed.

This article will focus on the small form of Lobelia cardinalis (submerged), also known as “dwarf” or “mini” Lobelia. This version of the plant is significantly smaller and more compact when maintained under optimal submersed conditions.

Lobelia cardinalis var. mini is widely used as a midground or foreground plant in Dutch style aquariums because of its interesting leaf shape and bright green foliage.

Also, Lobelia cardinalis cannot be categorized as a fast-growing species, it grows at a rather slow to moderate rate; therefore, making it easy to care for in an aquarium.

Keep reading for more information on Lobelia cardinalis, including how to properly grow and nurture the species in a freshwater tank.

Quick Notes about Lobelia Cardinalis var. mini 

Common Name Lobelia cardinalis
Other Names Cardinal flower, Red Cardinal, Blood-red Lobelia, Purple Lobelia, Mexican Lobelia, Emersed Dwarf Lobelia Cardinalis, Lobelia cardinalis mini
Scientific Name Lobelia cardinalis
Tank Size (minimum) 5 gallons (~20 liters)
Difficulty Easy
Lighting Moderate to high 
Optimal pH 6.0 – 7.5
Optimal hardness Soft to moderately hard water (2 – 12)
Optimal temperature 61 – 79 °F (16 – 26 °C)
Substrate Any 
Can float:
Can Be Grown Emersed:
Size: 4 – 8 inches (10 – 20 cm)
Growth Rate Slow to moderate (submersed), moderate (emersed)
Placement in Tank Foreground / midground
CO2 Not needed but recommended when submersed
Propagation Cutting, lateral shoots, and seed (emersed)

Interesting fact: Lobelia cardinalis once had ceremonial and medicinal uses for several Native American tribes. For example, the Iroquois used the Cardinal flower to treat fever sores, cramps, and upset stomachs.

Origin of Lobelia Cardinalis

Lobelia cardinalis, the cardinal flower, is a species of flowering plant in the bellflower family Campanulaceae.

It was named after the Flemish botanist, Matthias de L’Obel (1538-1616). The species was introduced to Europe in the 1620s, with the common name “Cardinal flower”; this is in reference to the red robes worn by Roman Catholic cardinals.

Habitat of Lobelia Cardinalis

Lobelia cardinalis is native to the Americas; Canada, United States, Mexico, and Central America to Colombia.

This species is found in humid areas, such as streambanks, ponds, wet meadows, and marshes. Therefore, the plant can be grown in aquariums, gardens, ponds, streams, etc. by meeting the conditions of its natural habitats.

Lobelia cardinalis grows in rich, medium to wet soil in full sun to part shade. It forms gorgeous red flowers that first mature in late summer and continue into mid-fall.

Description of Lobelia Cardinalis

Lobelia cardinalis is a sight to behold, having varying appearances in different habitats and environmental conditions. The emersed form also looks drastically different compared to submersed growth.

  • Emersed form:

Lobelia Cardinalis Care Guide – Planting, Growing, and Propagation - Emersed vs Submerged formWhen grown this way, Lobelia cardinalis can reach 4 ft (1.2 meters) in height. In open aquariums, where it grows above the surface, it forms lovely scarlet flowers and develops purple tints.

It also grows faster compared to submerged form.

Its leaves also appear dark green and purple underneath when grown emersed in nurseries with marshy conditions. These toothed leaves are arranged alternately. They grow up to 8 inches long (20 cm) and 2 inches broad (5 cm), and their shape vary from lanceolate to oval.

Due to their alluring appearance, they are helpful as vase flowers and garden flowers.

  • Submerged form:

In general, it looks like a completely different plant.

In aquariums, the leaves are much smaller (0.5-0.7 inches or 1.5 cm) and give only a beautiful shade of light green and appear as clear as green grass. Leaf veins are clearly visible; traverse foliage is smooth and well-formed with no marked distortion, serration, or any discoloration.

Do not buy this plant because of the purple color. Lobelia cardinalis gets it only when grown emersed. In the aquarium, the purple color will melt away and it will turn light green.
Lobelia Cardinalis (cardinal flower) Care Guide – Planting, Growing, and Propagation - Dutch aquariums (using the Leyden street technique)
Dutch aquascape with Lobelia Cardinalis – ‘the Leyden street’

The plant attains a maximum height of about 4 – 8 inches (10 – 20 cm) when grown in submerged conditions, so it’s clear why it is favored as a midground or foreground plant.

Also, levels of light exposure can influence how this plant looks. High light levels give it a more bushy, compact appearance whereas low lighting makes it grow scantly and slender.

These cool features have earned the species popularity and a deserved spot in the hearts of the Dutch. Thus, Lobelia cardinalis are commonly found in Dutch aquariums (using the Leyden street technique), typically placed in the midground and foreground sections.

Lobelia Cardinalis can be quite wild in its growth and look. Many daughter plants can develop from a single plant, extend and become dense. These new individual plants tend to overgrow with too many leaves, and thus, assume bushy growth forms.

Tank Requirements and Water Conditions

As I have already mentioned, this plant can grow in emersed or submerged environments that make this plant a great choice for garden ponds, terrariums, and paludarium setups.

You can achieve a beautiful-looking aquarium with this plant following the right approach.

Tank size: 

When it comes to tank requirements; there are no tank sizes that cannot be utilized. However, 5 gallons (20 liters) tanks are considered the minimum for growing this plant.

Water type, Temperature, Hardness, and pH:

Temperature: The temperature where this plant is grown should be appropriately regulated. A temperature range of 61 – 79 °F (16 – 26 °C) is just right for Lobelia cardinalis to thrive in an aquarium.

Note: This plant is very resilient. In the wild, Lobelia cardinalis can tolerate low temperatures up to 34 °F (1 °C).

pH: The pH level measures how acidic or basic the environment is to the plant. Keep the pH level between 6.0 – 7.5 to get optimal results.

Hardness: Lobelia cardinalis can tolerate but it does not like very hard water. It will thrive in soft to moderately hard water, ideally between the ranges of 2 – 12 GH.

Salinity: No, Lobelia cardinalis is not classified as brackish water plant; it does not tolerate well even low salinity levels. This species is not good for brackish tanks.  


Lobelia cardinalis grows better in a well-lit setting. Tanks with ample illumination are the best to grow Lobelia cardinalis. Research shows that its growth rate is extensively reduced under low light.

Low levels of light impact the appearance of the plant and attractive flowers and also affect the overall growth. Under lower light, Lobelia cardinalis puts out much more energy into growing vertically.

Therefore, the lighting should range from moderate to high.

Good lighting facilitates the production of some chemicals that ensure sufficient growth of the plant. The more light Lobelia cardinalis receives, the larger, showier, and more appealing it will be.

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The root system of this plant depends on its size and growth form. If grown emersed, Lobelia cardinalis develop a very strong root system that can reach 12 inches (30 cm) deep! When grown in submerged conditions, its roots are not that long and strong.

Lobelia cardinalis is a versatile plant. It absorbs nutrients through roots (substrate) and the water column from their leaves. 

Therefore, nutrient-rich substrates (such as ADA Amazonia, etc.) will be the best choice. However, with regular fertilization, this plant can grow in any substrate.

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CO2 and Fertilization:

CO2: CO2 supplementation is optional but as with most aquatic plants, Lobelia cardinalis grows best in water abundant in CO2 and essential nutrients. Such conditions help it to assume a healthy appearance and also improve the formation of leaves and lateral shoots.

Fertilization: Lobelia cardinalis requires both micro and macronutrients to thrive. Without proper nutrition, its growth will be very slow. Therefore, I’d say that fertilization is a must.

Note: It is better to use liquid fertilizers instead of root tabs. Although the plant can absorb nutrients from its roots system, I have seen a better growth rate with liquid fertilizers.

Important: If you keep shrimp in the tank with Lobelia cardinalis, I would highly recommend reading my articles:

The point is that a high level of CO2 and Copper (most fertilizers contain copper) is extremely dangerous to the shrimp.

Care and Maintenance of Lobelia Cardinalis

Lobelia Cardinalis (cardinal flower) Care Guide – Planting, Growing, and PropagationLobelia cardinalis is a relatively easy plant, the species does not demand specific requirements (except lighting and fertilization) to keep it thriving in your freshwater tank.

Pruning: As simple as it sounds, cutting down overgrown and old leaves is one of the significant methods of caring for this plant. Use sharp trimming scissors and cut off the lengthy stems and collect them for disposal or replanting.

In this case, the apical growth will stop and lateral shoots will go. This will make the plant very dense and bushy.

Planting and Propagation of Lobelia Cardinalis

Planting Lobelia cardinalis is straightforward, you need to place the specimens into a substrate having a thickness of 2 – 3 inches (5 – 7 cm) to prevent difficulty in rooting.

Another interesting feature of this plant is that it does not require a lot of spacing between plantlets to attain a nice, uniform look and more depth in the aquarium.

Dense groupings do not seem to hinder Lobelia cardinalis.

Dosing plant fertilizers after planting helps the plants form new shoots quicker and promotes healthy appearance.

Lobelia cardinalis is easily propagated by:

  • seed (when grown emersed),
  • cutting mature stems,
  • lateral shoots (near the base of the stem),
  • dividing daughter plants from the parent plant and placing them into the substrate.

Offshoots can be cut from the parent plant. You can also cut the top part of the plant just above a leaf, strip the bottom leaves so that you have 1 – 2 inches (2.5 – 5 cm) bare stem, and plant that into the substrate. After some time, the bottom will produce side shoots and the planted top will produce roots.

Note: In case you want to propagate by seeds, you can also use a dry start method. You will see the growth in 5 – 10 days after planting. Once Lobelia cardinalis has 3 – 5 leaves, it is ready to be transferred. This plant does transition well to submerged in high light.

Important: Lobelia cardinalis is a plant that grows out of water naturally and typically will not turn its beautiful purple color unless it is grown out of the water.

Problems Associated With Growing Lobelia cardinalis

These are some problems that you might face when trying to grow the Lobelia Cardinalis:

Diseases: Crown rot is a poor condition that affects some ornamentals like Lobelia cardinalis. This disease attacks the crown and over time causes other plant parts to wither.

Discoloration and leggy growth: The stems can get a yellow tint and stretch out.
Solution: It is recommended to cut off the stems.

Pests: Pests like pond snails can attack and devour the leaves and branches of this plant, especially when grown in outdoor ponds, nurseries, and gardens.
Solution: Remove pest snails and/or disinfect plants.

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Poor and Slender Growth: This problem is often caused by lack of CO2, low light, low nutrient levels, or a combination of all three factors.
Solution: When you witness such occurrences in your tank, you have to make necessary changes so as to help the plants return to normalcy.

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Toxicity: Almost all plants of the genus Lobelia are considered to be potentially toxic for humans and animals. Lobelia cardinalis is not an exception, it also contains a number of toxic alkaloids including lobelamine and lobeline.

Symptoms of ingestion of large quantities include nausea, vomiting, diarrhea, salivation, exhaustion, and weakness, dilation of pupils, etc.

Benefits of Lobelia Cardinalis

Aquascape: This beautiful plant can be an excellent decorative addition to Dutch style aquascapes.

No Overshadowing: It will not choke other aquatic plants. Lobelia Cardinalis mini does not grow very big. Thus, it will not block the light unlike many other tall and/or floating plants that can completely cover the surface of the aquarium in a short time.

Hiding place for fish, fry, and shrimp: Lobelia Cardinalis serves as cover and shade for inverts, small frogs, and fish.

Foraging place: Acts as a buffet of biofilm, which is an ideal first food for newly hatched fry and shrimplets.

Oxygenation: Lobelia Cardinalis oxygenates and aerates the tank water.

Lobelia Cardinalis and Compatible Tankmates

Lobelia Cardinalis is compatible with a wide variety of freshwater fish and invertebrates.

It can be grown in tropical aquariums containing freshwater fish species, as well as freshwater inverts such as:

Avoid or Be Careful:

Never attempt to keep Lobelia Cardinalis with crayfish, or freshwater crabs because they will most likely tear up the foliage and uproot the plant.

In the same vein, avoid hostile and aggressive fish species that are known plant devourers, these include Texas cichlids, Front cichlids, Jack Dempsey, Red Devil, and Oscars.

Buying Lobelia Cardinalis

This species is affordable and readily available at local fish stores and online aquarium stores. You can obtain a pot of Lobelia cardinalis for $5.

If there are several cultivars on display, consider the one that most appeals to you. While at it, opt for fresh and looking specimens devoid of poor health indicators such as rips, discoloration, curls, dead stems/leaves, etc.

In Conclusion

Lobelia cardinalis is a unique masterpiece for adorning the midground and foreground of freshwater aquaria, whether Dutch or Nature-styled.  It is an excellent beginner plant.

However, behind its beauty lies a need for proper maintenance. Additionally, the plant thrives under the right conditions — a mix of ample nutrients, lighting, and CO2.

So if you need an average-sized, vibrant and attractive plant for your fish tank — Lobelia cardinalis is the one!


  1. Lobelia cardinalis, cardinal flower, Campanulaceae. Florida Native Plant Society. 2015.
  2. Lobelia cardinalis, cardinal flower, Campanulaceae (bellflower family). Native Plant Database. 2015.
  3. Plant guide for cardinal flower, Lobelia cardinalis L. USDA NRCS. 2015.
  4. Natural selection on floral traits of Lobelia (Lobeliaceae): Spatial and temporal variation. American Journal of Botany. September 2003
  5. United States Department of Agriculture. Natural Resources Conservation Service.
  6. Native Aquatic and Wetland Plants: Cardinal Flower, Lobelia cardinalis. SS-AGR-398

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