How to grow Rotala Rotundifolia

Rotala rotundifolia 'blood red SG variant' - this variant gets redder more easily than other Rotala rotundifolia variants, but is still not wide spread in trade (2021). 

Introduction

Rotala rotundifolia (variants include Rotala Colorata, H'ra, Ceylon, etc.) is a fast-growing stem plant that has long been a staple of the planted aquarium world. It was first introduced around 1960 under the misnomer Rotala indica, a confusion that continues to this day. A description of the true Rotala indica can be found here - along with an explanation of how the names got mixed up.

It is tolerant of a wide range of water parameters and is an easy plant to grow; it will even do well in aquariums without carbon dioxide injection after a period of acclimatisation. However, with sufficient light and CO2 it will grow with better density and colouration.

As stem plants they will grow continuously towards the light and will reach the top of even high aquariums. If allowed to reach the water surface, it will eventually break through the surface and grow submerged leaves and flowers. If stems are planted in a high light aquarium with plenty of space around them, they will grow downwards and creep along the bottom. If planted in a more crowded area they will grow more vertically.

The plant will branch more when in rapid growth mode and will grow more vertically with less branching when conditions are low (either low CO2 or low nutrients).

Key success factors

• Sufficient light (80umols of PAR+) to get good coloration.

• Avoid extreme water parameters (high alkalinity or uncycled tanks).

• Higher nutrient levels combined with CO2 encourage the plant to produce more side shoots and become bushy. In poor conditions and without CO2, the stems are thinner and branch less frequently. CO2 and adequate fertiliser are required to produce the dense bushes seen here.

How to get it redder

• Stronger light (higher PAR). While the plant can grow in lower light levels, 80+ umols of PAR will promote better colouration. Stronger colouration is seen at 150-200 umols PAR. This level is easily achieved in the higher areas of the tank with good lighting systems.

• Low nitrates (5ppm & below), while maintaining other parameters high

Rotala Rotundifolia is one of the plants that will show redder colours under nitrate limitation - meaning that the plant will grow much redder when starved of nitrate. Overdo this and the plant will stunt. However, it is much more tolerant of low nitrogen levels than some other plants. If you decide to run a tank with low nitrate levels, make sure you choose a selection of plants that will adapt well to lean dosing conditions. You can read more about lean dosing on this page. It is more sensitive to water column NO3 levels than, say, ammonia in the substrate zone where colouration is concerned. The combination of having some ammoniacal nitrogen in the root zone and keeping the water column low in nitrates (NO3) will produce the best looking bushes overall. Too little nitrogen in both the substrate and the water column can result in thin plants with much less branching, making it difficult to form dense bushes.

The Seachem Nitrate Test Kit is one that has slightly higher accuracy readings for low NO3 levels for those who like to test their water.

The picture below shows Rotala H'ra under Twinstar S series lighting. It takes strong nitrate limitation to produce such deep red colours - NO3 levels would be virtually 0 on test kits. Note that she doesn't have a lot of branching and the overall bush density is average.

The same variant Rotala H'ra, when grown without nitrate limitation:

In this example, you can clearly see the exact point in the plant's growth cycle where pruning was applied in conjunction with nitrate limitation:

Another side by side comparison under same lighting:

There are many varieties of Rotala rotundifolia; Rotala 'blood red SG version' seems to be a variety that does not require as much nitrate limitation to be very red - making it a better choice for most tanks. However, this variety does not seem to be grown commercially and can be difficult to find in most countries.

Rotala 'blood red SG' is used in the background in this tank. Top view is below

Combination of rich substrate, low Nitrates in the water column, and high lighting produces striking reds with good bush density.

Propagation

Cut a few inches off the top of the plant and replant. New shoots will sprout from the nodes on the remaining stem. If the original plant was healthy, you can cut off most of the plant, leaving stems a few inches high, which will continue to sprout new shoots.

Even if you want a dense bush, plant the stems at least half an inch apart to allow room for side shoots. There should be enough space in the lower layers even if you want a dense canopy in the upper levels.

Trimming

Rotala rotundifolia takes well to pruning and forms dense bushes. It can be pruned repeatedly for many cycles before needing to be replanted with healthier/newer tops. This makes it very useful for aquascaping where the crest line needs to be maintained at a certain height for aquascaping purposes.

Pruning should initially be done about 4 inches below the final height you want your Rotala rotundifolia tops to be. (Unless you have planted your Rotala rotundifolia very sparsely to begin with, then trimming further down will allow more branching and density to build up.) As the tops grow out, cut off the ones that are growing faster than the rest - this will allow the shoots below to branch and the canopy to gain density as it grows upwards.

Once the canopy has reached the desired height, you should continue to thin it out by cutting off the tallest shoots and allowing new growth to take their place. This needs to be done very regularly (every 3 days or so). If, after a long period of not pruning, the canopy as a whole starts to grow, then you need to do a reset as above; cut the shrub much lower and let the tops grow out again. As with carpets - if you want to maintain it in the long term, you will need to prune very frequently. Growing the tank in lean conditions also slows down the overall growth of the plant and reduces the need for pruning.

Over a long period of time (months) the older undergrowth will deteriorate to the point where it is unhealthy. You should then allow the top to grow out longer and then replant the whole shrub.

Click here to find detailed steps on how to cycle a planted tank.