Bacopa caroliniana and Bacopa salzmannii 'Purple' are two aquatic plants that reward light with color: the first shifts from plain green to bronze and pink as PAR climbs, and the second holds a deep purple that runs right down the stem. Both grow at a moderate pace and can be propagated from simple stem cuttings. They sit best in the midground to background. While Bacopa caroliniana is an easy plant to grow, Bacopa salzmannii is a tad more demanding and require better conditions to show off its deep purple coloration. This article will cover how to attain healthy growth with these two species, and the common issues faced by aquarium hobbyists when growing these plants.
(Above) Bacopa caroliniana is larger, green with some reddish tones while Bacopa salzmannii 'Purple' is smaller but grows fully purple.
Bacopa caroliniana has a more colorful variant called Bacopa colorata that develops pink/bronze hues more easily than the more common Bacopa caroliniana. Common Bacopa salzmannii is not as deeply colored as the variant Bacopa salzmannii 'Purple', which was popularized by 2hr Aquarist when we discovered that the variant grew significantly more purple than the common Bacopa salzmannii. The variant was initially named Bacopa salzmannii "SG", SG being short for Singapore where we are situated. As the variant was later propagated by plant farms, the more universal name Bacopa salzmannii 'Purple' became more widely used instead. Hobbyists can sometimes still come across common Bacopa salzmannii, and the plant will look a lot more green compared to the Purple/SG version.
(Above) Top picture shows Bacopa salzmannii 'Purple'. Bacopa caroliniana is at bottom right, while Bacopa colorata is at bottom left. While the top few leaves of Bacopa caroliniana tends towards greenish tones even in high light, Bacopa colorata is more fully colored even in the new growth.
Quick answers:
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Bacopa caroliniana (lemon bacopa, blue water hyssop) is a green North American stem that takes on bronze and pink hues under strong light and grows up to around 60 cm. It is tolerant of moderately hard water conditions, and can be grown in low tech aquariums.
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Bacopa colorata is a more colorful variant of Bacopa caroliniana, and share the same growth requirements.
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Bacopa salzmannii 'Purple' is a smaller South and Central American species, roughly 15 to 30 cm, prized for its deep purple coloration. It needs better growth conditions to grow to good form and color. Not recommended for low tech aquariums.
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Better coloration for both species comes from light intensity and spectrum, CO2 injection, and steady all-round fertilization, not from dosing extra iron. CO2 injection helps coloration in both species.
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Both prefer soft water, though B. caroliniana tolerates hard, alkaline water while B. salzmannii does much better at lower KH levels (less than 4 dKH is ideal).
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Both species are stem plants and can be propagated by cutting above a node and replanting the tops; both species throw lateral shoots readily under favourable growth conditions.
How Do You Grow and Care for Bacopa caroliniana?
Bacopa caroliniana has long been a staple in the hobby and it well known to aquarium enthusiasts. Its most recognizable trait is the lemon scent it gives off when the leaves are crushed, which is why garden shops often sell it as lemon bacopa; it also goes by blue water hyssop. It is native to North America and grows in the wild in places such as the Everglades in Florida, tolerating even brackish water. This is a medium-sized stem plant, green in low light and taking on bronze to pink hues as light climbs. It works well planted in small groups in the midground, and will grow tall, up to around 60 cm, if left unpruned. It can be trimmed repeatedly to keep it down to size. Tops can be replanted as well to control its height.
Hardiness is the draw of this species. B. caroliniana tolerates hard, alkaline water though it thrives in soft water. It grows in roughly pH 6.0 to 8.0 and 2 to 15 dGH, and sits comfortably in typical tropical temperature range of 68 to 86°F (20 to 30°C). It grows larger and colors up more in softer water. Plant it in a bright spot rather than the shade: this is a light-hungry plant, and the bronze and pink tones only show when it gets enough light. Intense light with long photo-periods are one way to sun tan the plant into more reddish tones. "Full spectrum lighting" is a marketing term and is not indicative of the quality of a light. Aim for 150 umols of PAR if you are looking to get nice pink and bronze tones in this species.
If you are looking for color, Bacopa colorata is the more ideal species to grow. It shares the same growth characteristics as Bacopa caroliniana, but its leaves are more pinkish. CO2 is beneficialwhere color is concerned. Grown without injection, B. caroliniana will be mostly green; add CO2 and you get larger, more robust plants with markedly better growth and coloration.
Growth speed of Bacopa caroliniana is moderate, which is part of its appeal, since it does not need topping as often as faster growing stem plants.
(Above) Bacopa caroliniana on the left and Bacopa colorata on the right. Both gain bronze and pink tones under higher light, CO2 injection and regular fertilization.
How Do You Grow and Care for Bacopa salzmannii?
Bacopa salzmannii is native to the wetlands of South and Central America, where it grows in swamps and along the banks of rivers and ponds. It is about half the size of B. caroliniana, with a mature height around 15 to 30 cm and small, oval leaves, and it comes in several varieties. Depending on the variety, color ranges from green with a hint of purple through to deep purple.
(Above) Bacopa salzmannii in front of Bacopa salzmannii 'Purple'. The common greenish variety beside the deeper purple form, grown under the same conditions and shot in the same light. The contrast is stark enough that they almost read as different plants.
Unlike the hardy B. caroliniana, Bacopa salzmannii is a more demanding species to grow well. It is more picky about water hardness and does much better in soft water with low alkalinity. It grows in roughly pH 6.0 to 7.5 and 2 to 15 dGH, and sits comfortably in typical tropical temperature range of 68 to 86°F (20 to 30°C). It prefers KH to be below 4dKH.
Plant it in a bright spot rather than the shade. Moderate to high lighting is crucial for the deepest purple hues. 150umols of PAR is sufficient to get vibrant color in Bacopa salzmannii. CO2 is not optional if you want good color. Low CO2 in an otherwise high-tech tank shows up fast as poor coloration, and that quick fade is one of the more reliable signs that CO2 has dropped. Injected tanks color up in a way low-tech tanks cannot match, because carbon is the limiting factor: around half of a plant's dry mass is carbon, so nothing else you dose compensates for a shortfall in it.
Good light levels, coupled with CO2 injection, and steady all-round fertilization will carry that purple right down to the stems. Its growth speed is also moderate for a stem plant.
As stem plants that get topped and replanted often, they draw most of their nutrients from the water column while their cut roots grow back in, so water column dosing does the heavy lifting here. A rich or aquasoil substrate still helps: it supplies ammoniacal nitrogen, which gives a boost to growth rate and robustness. You do not need a nutrient-rich substrate to grow them, though. The plant will grow in plain sand or gravel; in that case, lean on the water column and, if you want more from them, enrich the root zone with tabs. Leaf size is a good indicator whether the plant is getting sufficient macro-nutrients. Deterioration of lower parts often indicator unstable nutrient levels or overly lean macro-nutrients.
B. salzmannii 'Purple' contrasts well with both red and green plants and, for all its color, stays relatively hardy. It sits best in the midground or background. It is safe for shrimp tanks and untroubled by typical community fish and snails.
Common issues: Deteriorating Lower Leaves and Algae on Bacopa species
This is less of an issue in Bacopa caroliniana but common in Bacopa salzmannii. Bacopa salzmannii is a tad more sensitive to stability of growth parameters and the environment. Both fluctuations in CO2 levels or nutrient levels can cause lower leaves to deteriorate, even though new growth seems fine. The solution to badly deteriorated lower growth to do topping and replanting. Uproot the entire plant, discard the deteriorating bottom portion and replant the healthy top growth.
Fluctuations in growth parameters and organic waste levels often cause algae to attach to lower leaves. Regular water changes and good tank maintenance plays a large role in growing these plants well.
When nutrient levels or CO2 is too low, Bacopa salzmannii will produce smaller leaves and thinner stems. This is usually also coupled with pitting and deterioration in older leaves. This can be rectified by heavier water column dosing or by enriching the substrate.
How Do You Propagate Bacopa caroliniana and Bacopa salzmannii?
Both species propagate the same simple way: cut above an internode and replant the top 2 to 3 inches. Both throw lateral shoots naturally over time, and you can cut those side shoots at the nodes to make more plants. When the plants are healthy, they recover well from topping. The rooted portion will grow new growth heads along the leaf nodes.
After a few pruning cycles the lower portions of the original stems usually deteriorate while the fresh tops root in on the old internodes. When that happens, replant the fresh tops and uproot and discard the old bottoms. Regular pruning promotes healthy, bushy growth and keeps the plant compact rather than leggy. Grown emersed, in a paludarium or Wabi Kusa arrangement, both adapt readily and can throw small white flowers and pale blue flowers.
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