How to grow Rotala macrandra & its varietals

Variegated Rotala macrandra is shown above; it has a more magenta red colour compared to regular red Rotala macrandra with distinctive white veins. Similar in size to regular Rotala macrandra, but harder to grow well.

Introduction

Rotala macrandra originates from India and has been cultivated in aquariums since the early days for its attractive foliage. It is a fast growing stem plant with a reputation for being a difficult plant to grow well. Rotala macrandra has larger leaves and is more difficult to grow than the more common Rotala rotundifolia and is best used in the middle or background of an aquarium. Its leaves are delicate and are easily broken by rough handling. Most varieties will readily branch when growth requirements are met, allowing them to become dense bushes.

There are many cultivars and different morphs of Rotala macrandra. The green cultivars are generally the easiest to grow, the red cultivars are more difficult and the variegated and mini cultivars (including 'mini butterfly' and 'mini/pearl types 1 to 4') are considerably more difficult. If we add the 'narrow leaf' versions and variations from different regions, there are more than 10 different forms that can be included under the general umbrella of Rotala macrandra.

A mix of Rotala macrandras offers a wide range of colors and leaf shapes. 

Rotala macrandra 'mini type 4' green shows nice orange tones under high light. Note the serrated leaf margins. It provides a good contrast to other red and green plants in the tank.

Rotala macrandra 'narrow leaf'

Rotala macrandra 'mini type 2' has very unique curled leaf margins. However, it is a difficult plant to grow consistently well.

Rotala macrandra 'mini butterfly' looks similar to Rotala rotundifolia red at first glance, but has a deeper shade of red with leaf edges that are slightly rolled outwards. It will take on a more compact, rounder form under slower growing conditions.

Rotala macrandra 'mini type 4' red from our 2hr farm tank. The leaves are about 1/3 the size of regular Rotala macrandra. Substrate PAR is around 200 umols, water column fertilisation is low with rich substrate.

Growth requirements

Although there are many cultivars, they all have the same growth requirements - the more difficult cultivars will simply stunt and grow poorly quickly if the requirements are not met, while the easier cultivars are more forgiving. Rotala macrandras are one of the best indicator plants in the aquarium, changing their growth forms with great variability depending on the growth conditions in the tank.

Rotala macrandras grow best in soft water (low KH < 3 dKH / low alkalinity). The hardier cultivars (such as the regular Rotala macrandra red/green) can grow decently in moderately hard water (8+ dKH), but the more delicate cultivars such as the variegated or mini types are best grown in very soft water. (The exception is 'mini type 4' which seems to be hardy).

Rotala macrandra grows best with CO2 injection. Rotala macrandras generally do not require very high CO2 levels, but they do not tolerate CO2 fluctuations well. So CO2 levels need to be kept at a steady level (long term) whether you choose a higher or lower injection rate. Dips or inconsistent CO2 levels can easily lead to tip stunting in the more finicky varieties. Lower injection rates can result in more compact and smaller growth forms, along with slower growth. There will also be less branching at low CO2 levels. Higher injection rates will produce larger, more robust plants - this will be more beneficial for newly introduced, adapting or damaged plants. At higher CO2 levels there will be more branching off the main stem and a much faster growth rate. Fast growth also means there is less room for error in fertilisation - if fertilisation is too low when light and CO2 levels are high, there will be premature deterioration of the lower leaves.

Both plants were cuttings taken from the same plant and grown under different conditions. Less fertiliser and lower CO2 will give slower growth and more compact forms, while higher CO2 and fertiliser will give larger forms.

Rotala macrandra needs regular fertilisation to get the best shape and colour. Ammonia at the root zone (mainly through the use of enriched aquasoils) gives a significant boost to stem thickness, leaf and crown size and the overall robustness of the plant. Despite being a fast growing stem plant, Rotala macrandras responds well to root feeding. If macro-fertilisation is lacking, the older leaves and lower stems will start to deteriorate. This can be quite rapid in fast growing conditions (high light, high CO2) but will take longer in slow growing conditions (low light, low CO2);

Micro nutrient (Fe/trace) problems tend to manifest themselves in colouration (faded or poor colouration can indicate insufficient iron/trace) or poor micro-nutrient mixes (excessive leaf curling).

These plants are grown in an ammonia enriched substrate - this results in thicker stems and rounder, fuller leaves.

Rotala macrandra 'mini type 4' green.

Rotala macrandra 'mini type 4' red.

The crown and upper leaves should be of a similar size to the lower leaves. Decreased crown size is the first indication that the parameters are not optimal.

Stunting tips in Rotala macrandra

Tip stunting in Rotala macrandra 'narrow leaf' compared to normal growth on the right. Both plants were from the same batch of plants but grown under different fertilisation regimes.

Tip stunting is a common occurrence in Rotala macrandra. Contrary to popular belief, tip stunting is rarely associated with a lack of macro-fertilisation - which manifests itself in poorer colouration and smaller plants. It is almost always associated with sudden drops in CO2 levels or excessive water column fertilisation. (or high NO3 levels due to livestock). Too low macros in the long term will lead to deterioration of the lower leaves first, not the tops. Higher macro fertilisation works in soft water (less than 3KH). If you see tip stunting in your Rotala macrandras, it is highly recommended to move nutrients from the water column to the substrate. This means using a richer soil/aquasoil while reducing the amount of liquid fertiliser in the water column.

All samples below are from the same genetic stock/mother plant but grown in different soft water tanks.

Tip stunting (left) vs normal healthy growth in Rotala macrandra 'mini type 4'.

Tip stunting due to over-fertilisation (left) vs. under-fertilisation (right). Note that the left sample has a deeper colouration than the right sample. Overfertilisation can lead to more faded colouration/paler leaves and, in extreme cases, premature decline of the lower leaves - but does not lead to tip stunting. Both stems are Rotala macrandra 'mini type 4'.

Rotala macrandra 'mini type 4' in optimal fertilisation (left) vs. slightly too lean (right). The colouration is slightly faded in lean conditions. Colouration is also highly dependent on light spectrum and quantity (PAR values).

As with many plants in the Lythraceae family, Rotala macrandras grow most stably with rich root fertilisation and a lean water column. Too rich a water column fertilisation (especially high NO3 levels) with harder water will easily lead to stunted tips (although this can work if your water is very soft). In this sense, the harder/more alkaline your water, the more plants should be root fed rather than water column fed. * Vin Kutty's 2019 AGA talk covers this topic extensively. The running hypothesis is that this family of plants has problems regulating nutrient uptake through their leaves, especially in harder/more alkaline water, so feeding them through their roots will give much more stable results.

We use Rotala macrandras sometimes in our Seiryu (limestone) aquascapes. Rotala macrandra mini type 4 is shown above grown in  8 - 9 dKH water, with rich soil / lean water column fertilization. The form is not as full and the coloration is a tad lighter compared to plants grown in softer water, but it grows pretty steadily otherwise.

Key success factors

• Stable water parameters and stable CO2 levels (sudden dips in CO2 levels can cause tip stunting)
• Soft water/Low KH levels are very helpful (3 <dKH) for picker varietals
• Many species can be grown in more alkaline water with richer root feeding, leaner water column fertilization. (watch for tip stunting)
• Better light spectrum (stronger percentage red/blue) and higher PAR values gives better coloration for red varietals
• Slower growth parameters, higher light values give shorter inter-nodes
• Avoid shading

Trimming & propagation

Rotala macrandra is a fast-growing stem plant, so propagation is easy; cut off the top 3 to 4 inches of the stem and replant, leaving the bottom part to sprout new shoots. Robust cultivars, such as the green cultivars, can withstand several topping cycles before the new tops need to be replanted and the old bottoms discarded.

Rotala macrandra 'mini type 4' green under strong lighting.