Scarlet Ludwigia Care Guide (Ludwigia sp. 'Scarlet')
Scarlet Ludwigia is one of the easiest ways to bring a warm scarlet-red accent into a freshwater aquarium. It is a stem plant (an upright plant grown as a leafy stem and propagated from cuttings), carrying slim, pointed leaves that shade from olive or bronze-green through to a vivid orange-red and scarlet under good light. Hobbyists reach for it because it delivers that eye-catching red colour while staying genuinely forgiving — like the other easy red Ludwigia it will grow and colour up without pressurised carbon dioxide, and it settles happily into most planted community tanks. The one wrinkle is its name: "Scarlet Ludwigia" is a trade label rather than a single botanical species, and what arrives under it can be any of several closely related red Ludwigia.
1. Species Overview
"Scarlet Ludwigia" is a common trade name, not an accepted botanical species, and it pays to be upfront about that. Our store lists it as Ludwigia sp. 'Scarlet', and every plant sold under the name belongs to the genus Ludwigia in the evening-primrose family (Onagraceae), a group of amphibious American and cosmopolitan wetland plants. Beyond that, the identity genuinely varies from supplier to supplier. Most often the name is attached to the natural hybrid Ludwigia repens × arcuata — a cross found wild in Florida, with narrow, lance-shaped leaves that flush blood-red — which is how Aquasabi and the Flowgrow database catalogue it. Just as often it refers to a red form of Ludwigia palustris, the near-worldwide marsh seedbox, sold variously as 'Super Red', 'Mini Super Red', Ludwigia sp. 'Red' and, confusingly, sometimes under the old label 'natans'; Tropica, the 2Hr Aquarist and Buce Plant all treat these as one and the same plant. And some sellers — including Australian listings — simply catalogue Scarlet Ludwigia as a red Ludwigia repens with narrow, scarlet leaves. Like most stem plants it is amphibious, usually grown emersed (with its leaves above the water) at the nursery, so fresh stock often converts its first leaves as it settles into fully submersed life. The practical upshot is reassuring: whichever of these you receive, it is a red-leaved Ludwigia with very similar needs, so the care below applies to a red Ludwigia generally. We would rather be honest that the exact species is uncertain than pin a single Latin name on a plant that travels under several.
2. Difficulty Level and Suitability
Honestly rated, Scarlet Ludwigia is an easy to easy–moderate plant, and the sources behind its various identities agree closely. Tropica rates Ludwigia palustris 'Super Red' as easy; Aquasabi and Flowgrow both rate the repens × arcuata hybrid easy; the 2Hr Aquarist calls the red palustris forms easy and "not particularly fussy about water parameters"; and Australian retail listings rate their Scarlet Ludwigia as relatively easy, around four out of ten for difficulty. Where a little nuance creeps in is the gap between growing the plant and colouring it: every source agrees it grows readily, but the deep scarlet most people are picturing wants stronger light and steady iron. Grown dim it tends to stay green, stretch and shed its lower leaves; given more light and a little feeding it turns compact and richly red. That makes it a fine choice for beginners, low-tech tanks and planted community aquariums, while still rewarding a keeper who adds more light, iron and — where they have it — CO₂ with markedly better colour. It does not need CO₂ or high-tech gear to survive, only to look its best.
3. Water Parameters
Scarlet Ludwigia is more concerned with steady, well-lit, adequately fed water than with hitting an exact figure, and because the name covers more than one species the published sources vary, so treat the numbers below as working targets rather than strict limits.
| Parameter | Target range | Notes |
|---|---|---|
| Temperature | 20–28 °C | A warm-water tropical plant with useful cool tolerance. Australian retail listings quote 20–28 °C; Flowgrow gives Ludwigia palustris an optimum of 22–26 °C and the repens × arcuata hybrid 24–28 °C, both listing tolerance well down into cool water. Growth slows when cold. |
| pH | 6.0–7.5 | Adaptable. Australian listings quote 5.5–7.5, Flowgrow 5–8 for both the palustris form and the hybrid, and Buce Plant 6.0–7.0; slightly acidic to neutral tends to bring out the best red. |
| GH (general hardness, the amount of calcium and magnesium in the water) | 3–12 dGH (adaptable) | Soft to moderately hard water both suit it. Australian listings quote 3–8 dGH while Aquasabi lists tolerance up to about 30 dGH; softer water tends to favour slightly better colour. |
| KH (carbonate hardness, the water's buffering capacity) | 2–12 dKH | Australian listings quote 2–8 dKH; Flowgrow lists tolerance up to 22 dKH. Lower, softer buffering helps CO₂ work and can deepen the colour, but it is happy in harder water too. |
| Nutrients / substrate | Column and root feeder | Takes nutrients through both leaves and roots. As a red plant it colours best when iron and trace elements are available, so a nutrient substrate or root tabs alongside light water-column dosing gives the strongest colour. |
The main thing to appreciate is how tolerant these red Ludwigia are: they settle into most tap-water tanks without special treatment, so the real levers for a good result are light and iron for colour rather than an exact pH or hardness. Keep some nitrate present so the plant never starves, and let stable, well-lit, well-fed water do the work.
4. Lighting Requirements
Light is the master switch for this plant's colour, and it is the one area where the sources genuinely pull in different directions. Using the PAR bands common to our guides — PAR (photosynthetically active radiation, a measure of usable light reaching the plant) of roughly 30–50 counting as low, 50–80 as medium and 80-plus as high for plants — Tropica rates the light demand of its Ludwigia palustris 'Super Red' as low, whereas Buce Plant and many retail care sheets call for medium-to-high light, and the Flowgrow entry for the hybrid spans low all the way to high. The 2Hr Aquarist ties the numbers together usefully: the plant will grow at around 40 PAR (low light), but roughly 70–80 PAR and above is what produces good red colouring. The honest working position, then, is that Scarlet Ludwigia grows under low-to-medium light but colours up under medium-to-strong light — the more light it gets, within reason, the redder and more compact it becomes, while too little leaves it green, leggy and bare at the base. There is a ceiling to chasing brightness, though: strong light without matching nutrients simply invites algae onto the leaves, so if you move a plant into a brighter tank, raise the light gradually over a week or two and let it acclimatise rather than melt.
5. CO₂ and Fertilisation
Like all plants, Scarlet Ludwigia grows by photosynthesis — using light to turn carbon dioxide and nutrients into new tissue — so the amount of available carbon affects how fast and how densely it grows. A large part of this plant's appeal is that added CO₂ is genuinely not required: Tropica rates the CO₂ demand of the palustris form only "low", Aquasabi states the hybrid needs none, and both the 2Hr Aquarist and Buce Plant describe CO₂ as helpful rather than necessary, the 2Hr Aquarist noting that even a little — from about 10 mg/L — improves colouring. Flowgrow lists a beneficial band of roughly 10–40 mg/L for both the hybrid and the palustris form, so if you do inject, a stable level in that range gives faster, denser, slightly deeper-coloured growth: a bonus rather than a requirement. On feeding, treat it as a plant that draws nutrients through both roots and leaves, so a nutrient substrate or root tabs alongside regular water-column dosing works well. For any red plant, iron and trace elements are the key to driving and holding the colour, and here the sources differ in an interesting way. Much red-stem lore holds that keeping nitrate deliberately lean pushes the colour redder, yet Buce Plant reports the opposite for these palustris-type reds, linking generous nitrate, phosphate and iron to the brightest scarlet. The safe reading across both camps is to keep the tank fed rather than starved, and let light and iron do the real colouring.
6. Planting and Placement
Plant Scarlet Ludwigia as the stem plant it is: separate the bunch into individual stems, remove any rockwool or lead weight, and push each stem a couple of centimetres into the substrate, spaced a little apart rather than crammed together, since a tight clump traps debris and rots at the base. Strip the lowest leaves from the buried portion. It belongs in the midground or background, where a group of stems makes a warm scarlet accent against green neighbours — the narrower-leaved hybrid forms in particular give a soft, feathery look. Give it room to rise: sources put its height at roughly 15–40 cm, and Buce Plant notes that ungroomed stems can push well past 50 cm, so place it where it will not shade shorter plants in front, and trim it to sit lower in the midground if you prefer. It also grows happily as a floating stem, the trailing tips colouring up strongly close to the light, which is a handy way to grow a batch on while a display fills in. Being a stem plant it has no rhizome, crown or bulb to worry about — plant the stems individually and trim and replant regularly to keep a group dense rather than bare-legged.
7. Growth Rate and Propagation
Growth is best described as fast, with one dissenting voice worth noting: Flowgrow, Aquasabi and Buce Plant all call the red Ludwigia forms fast — Buce Plant even "very fast" — while Tropica rates its palustris 'Super Red' only "medium". Expect brisk, steady growth that needs regular trimming rather than an explosion. Propagation is the standard topping-and-replanting of stem plants: once a stem has some height, cut the top few centimetres off cleanly, just above a leaf node, and replant that top directly into the substrate, where it quickly roots. The cut base then branches and sends out side shoots, growing bushier, and those shoots can in turn be snipped and replanted to build a fuller stand — replanting the freshest, reddest tops keeps the best colour on show. Much commercial stock is grown emersed at the nursery or sold as tissue culture, so plants often arrive with firmer, greener above-water leaves that are shed and replaced by softer, redder submersed growth once they settle. That transition is normal, and the new submersed leaves are the ones to judge the plant by.
8. Common Issues and Troubleshooting
Most troubles with Scarlet Ludwigia trace back to light or feeding rather than to any fussiness, because it is otherwise very tolerant. The commonest early surprise is melting or leaf drop soon after purchase, as nursery plants grown emersed or in tissue culture die back their first leaves on the switch to submersed life — this is normal, so keep conditions stable and let the new leaves come through. If the plant stays green and refuses to redden, the cause is almost always too little light or too little iron; raise the light gradually and dose iron and trace elements. Long, bare lower stems with dropped leaves are the classic sign of insufficient light, so lift the lighting, or simply top the plant and replant the healthy tips to restart it lower down. Stunted or pale new tips point to a nutrient shortfall — usually iron — or, if you inject CO₂, to swings in the CO₂ level, so keep dosing steady and, where used, keep the gas even through the photoperiod. Holes and yellowing in older leaves signal a deficiency, often iron or potassium, and respond to balanced dosing. Finally, because strong light on an underfed plant favours algae, you may find it settling on the slower lower leaves where the light outruns the nutrients; improve flow, rebalance dosing and trim the worst-affected leaves so cleaner growth can take over.
A Note on the Ranges Above
The parameters and other figures in this guide are a general guideline only. Every planted aquarium is different, and the ideal balance for Scarlet Ludwigia depends on your lighting, your substrate, your other plants and whether you run CO₂. For help working out tank volume and the right dose of fertiliser, plant food and treatments for your system, have a look at our Aquarium Calculators.
Disclaimer
This guide is provided for general educational purposes only. It is not a substitute for professional advice, and we cannot guarantee outcomes. Individual plants vary, and the right conditions for your system depend on your lighting, your equipment and the other livestock and plants you keep. If you are unsure about anything, please get in touch with our team before proceeding.