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 displaying nice orange tones under high light. 

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. The leaves are about 1/3 the size of regular Rotala macrandra. Substrate PAR is around 200 umols.

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 (less than 2dKH). 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. 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. Higher injection rates will produce larger, more robust plants. At higher CO2 levels there will be more branching off the main stem. 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.

Nitrate limitation does not deepen red pigmentation for Rotala macrandras. Limiting nitrogen availability just results in less branching and less bushy plants.

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. 

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. Poor trace mixes can also lead to tip stunting and leaf curling.

Rotala macrandra 'mini type 4' green. Grown under lean water column (less than 5ppm residual NO3 in the water column), rich substrate.

Rotala macrandra 'mini type 4' red. Nitrate levels in this tank measure around 15-20ppm, demonstrating that low nitrate levels are not required for strong pigmentation.

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 (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. Under fertilisation 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).

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 due to a lack of fertilisation - which manifests itself in poorer colouration and smaller plants, not in stunted tips.

Plants are constantly adapting their internal machinery to make optimal usage of available resources in the environment. When a large change in the environment occurs, the plant has to re-configure its enzyme levels to match the changes. When the adaptation response is particularly sharp due to a big change in the environment, it causes a dramatic pause in growth that manifests as stunting tips. If the plant succeeds at adapting to the changes - new growth shoots will be produced. If the plant fails at the adaptation phase, the plant will deteriorate and die. 

There are 3 common causes for stunted tips

1. Sudden drops in CO2 levels.
2. Large changes (both upwards and downwards) in nutrient values (principally nitrogen availability).
3. Over fertilization in micros elements relative to growth rates.

The biggest factors that trigger aquatic plant adaptation responses are CO2 availability and nitrogen availability.While plants seem to adapt easily to increased CO2 saturation without issues, downward changes in CO2 availability and large changes in nitrogen availability (both upwards and downwards) cause significant plant re-programming and tip stunting.

Rotala macrandras favor a stable growth environment where growth parameters are kept consistent as their re-programming response to changes is particularly sharp. However, what exactly makes for a stable growth environment?

Tank Example 1. 

Tank starts week at 0ppm NO3. Daily dose of 2ppm NO3. Plant uptake rate of tank is 2ppm NO3. Tank measures consistently 0ppm NO3 residual levels in the water column. This is an example of lean dosing, leading to consistent residual levels (zero or near zero residual water column NO3). Plants adapts to having 0ppm residual NO3. This is an example of zero bound stability.

Tank Example 2.

Tank starts week at 0ppm NO3. Daily dose of 4ppm NO3 a day. Plant uptake rate of tank is 1ppm of NO3 a day. This causes a net daily accumulation of 3ppm a day. Tank starts week at 0ppm of residual NO3 a day, rising to 21ppm of residual NO3 after 7 days. This is an example of heavy dosing, but inconsistent residual nutrient levels. The plant that started out adapted to growing at 0ppm residual Nitrate levels now will start adapting to high nitrogen availability at the end of the week due to spike in NO3 levels. This will induce an steep adaptation response in many plants. This is an example of unstable tank environment. Aquariums run this way will always be more vulnerable to algae due to plant re-programming response.

Tank Example 3.

Tank starts week at 15ppm of NO3 in the water column. Daily dose of 3ppm of NO3. Plant uptake rate of tank is 3ppm of NO3 a day. Tank measures consistently 15ppm of NO3 in the water column. Plants adapt to having 15ppm NO3 in the water column. This is an example where residual water column nutrients are high, but consistent. This also produces a stable growth environment.

Zero bound stability/nitrate limiting tank (Tank example 1)

This is one approach that is easy to execute to maintaining consistent water column nitrogen levels: using a rich substrate while dosing more on lean side. This has given rise to the observation that many Rotala macrandra varietals seems to be easier to grow in rich aquasoil substrates. However, the mechanism on which this works is that it is easier to have low stable water column nutrient levels when the plants can feed from a rich substrate.

We use an example where plant uptake rates match or exceed fertilizer dosing rates (using nitrate as a proxy) on a daily basis. Such a system will have no net accumulation of nitrates in the water column. This means that any nitrate dosing is fully taken up by plants. Nutrient build up = Fertilizer dosed - Plant uptake. The build up rate for Nitrates in this tank is 0ppm daily.

The downside of running such a system is that less competitive species could be starved of nutrients if the dosage falls far below what is required. Aquarists have to observe their plants closely to detect whether they are under-dosing. The way to get around this is to use a rich substrate where plants can get additional N through the substrate if they require.

In reality, up take rates for plants can mismatch against fertilizer dosing rates. Many folks may also want to dose at least slightly in excess to cover any fear of under dosing. By dosing slightly more than the average uptake rate of our tanks, we can easily manage nutrient levels by doing a large water change reset at the end of the week. A more realistic nutrient accumulation chart would look like the one below where plant uptake fluctuates within a zone even when nutrient dosing is kept consistent. A large water change (80%) is done each week to reset levels. If you are always over-dosing slightly in excess, doing a large water change each week (much more than 50%) is highly recommended to reset levels. Nutrient build up = Fertilizer dosed - Plant uptake (cumulatively). The build up rate for Nitrates in this example varies from 0-0.8ppm per day.

In this above example, accumulative nitrate levels keep below 5ppm consistently with some room for error. This is an example of a system where there is slight excess, but nitrates availability never rise enough for plant-reprogramming to occur.

An example of tank grown with lean dosing combined with rich substrate. Water column nitrate levels never rise above 5ppm in this aquarium. Many species can grow well in such an environment as long as they are rooted in rich aquasoil. Tank above is grown with a combination of APT Feast and APT3. The nitrate limiting impact of this approach gives slower growth rates and also brings out reds in species that respond well to nitrate limitation.

Unstable dosing example (Tank example 2)

This is an example of a tank that is dosed 3 times a week with high dosage of nitrates. The tank then gets a 50% water change at the end of the week.

This is an example where heavy water column dosing relative to plant up take rates causes nitrate levels in the tank to fluctuate in a large range, which causes significant plant re-programming. This often leads to algae spikes as well as stunting for sensitive species. For most planted tanks, a 10ppm nitrate increase/decrease is a significant enough change to stress sensitive plants such as Rotala macrandra.

A better way to maintain high water column nutrient availability in a stable manner is described below.

EI style dosing in a stable manner (Tank example 3)

In this example, we will dose the same amount of nutrients per week as the unstable example (Example 2) above. Plant uptake rate are also kept similar to above. However, the way we divide the dosage is changed significantly. Instead of dosing 9ppm three times a week as above, we now divide the dosage to 3ppm daily. However, on the last day of the week, we do a large water change and do a triple dose to replace nutrients that we removed during the water change. Nutrient buildup = Fertilizer dosed - Plant uptake (cumulatively). The build up rate for Nitrates in this tank is 1ppm daily.

Even though the same amount of fertilizer is dosed across a week for both examples, we have managed to even out the nutrient buildup across the week with this approach.

Rotala macrandra mini type 4 green and red. 

This tank is balanced around having 15-20ppm of residual nitrates in the water column. Tank above is grown with APT Feast and APTe. To maintain higher residual water column nutrient levels, measurements are taken periodically to check the uptake rates and matched with an appropriate dosing rate. For the 360 litre tank above, the dosage worked out to be around 7ppm of APTe in a day. However, this may change over time as plant mass increases and the aquasoil depletes. Rotala macrandras can grow well in high nutrient values as long as the values are kept stable.

Large water changes remove a build-up of nutrients, while nutrients are re-dosed after water changes to stay within the target zone. This approach requires more work at taking measurements and calibrating fertilizer dosages as each tank's uptake rate can be quite different. For many folks, this may be a more difficult approach than the zero bound approach. The advantage of having higher nutrient values in the water column is that some difficult to grow species will propagate much faster. Higher water column nutrient values also means one can pay less attention to maintaining substrate richness.

Rotala macrandra in harder water?

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 nutrient parameters and stable CO2 levels.

• Soft water/Low KH levels are very helpful (less than 2dKH) 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

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.

After a few trimming cycles, Rotala macrandras benefit greatly from topping and replanting. Firstly, the entire Rotala macrandra bush is uprooted. The aquasoil area is cleaned of excess organic dust by using a turkey baster to stir up the substrate. This step is important. New ammonia enrich aquasoil is added if the soil is depleted.

Then the uprooted stems are sorted; only the largest, healthiest tops are cut to length and replanted.

Click here to find out how to grow red aquarium plants.

Click here to read on how to optimize CO2 levels

Click here to browse more plant growing profiles

Click here to read on how to stabilize a new planted tank