Rotala rotundifolia is the stem plant people grow when they want colour. Under strong light with added CO2 the tops turn red and orange, and it grows fast enough to fill a background quickly. In lower light it stays green and grows perfectly well, just without the colour it is known for.
Getting the colour
Rotala rotundifolia colours red and orange under high light with added CO2. Both parts matter. Strong light is what triggers the colouring, and CO2 is what lets the plant use that light rather than handing the advantage to algae.
Green Rotala is not a failure. It is what the plant looks like in a low-tech tank, and it grows readily there. If the colour is the reason you want it, be honest about whether your tank can supply the conditions before buying it.
Trimming and propagating
| Requirement | Rotala rotundifolia |
|---|---|
| Light | Medium to high |
| CO2 | Beneficial |
| Difficulty | Easy to medium |
| Growth rate | Fast |
| Placement | Stem, background |
Fast growth means regular trimming. Cut the stems and replant the tops, which is the standard way stem plants are propagated and the reason a single pot turns into a full background over a couple of months.
That trim-and-replant cycle is the entire discipline of the Dutch style, where tiered rows of stem plants carry the whole composition and the tidiness is what gets judged.
Rotala questions
Why is my Rotala rotundifolia green and not red?
Not enough light, most likely. The plant colours red and orange under high light with added CO2, and stays green below that. It is healthy either way.
Does Rotala need CO2?
Not required, but beneficial, and effectively necessary if colour is the goal. It grows without it in medium light as a green background plant.
How do you propagate Rotala?
Cut a stem and replant the top portion in the substrate. It roots readily, and the cut stem branches below the cut, so trimming thickens the stand as well as multiplying it.