Introduction

Stem aquatic plants offer a huge variety of colours and leaf shapes, but hobbyists are often intimidated by them. A common experience for newer hobbyists is that the stem plants grow well for a period of time, then after a few trimming cycles the lower stems deteriorate and the aquarist is at a loss as to what to do. In this guide we will explain how to keep aquatic stems in good condition for the long term.

A large number of plants in the aquarium trade can be categorised as stem plants. They come in a wide variety of colours and leaf shapes. Stem plants grow steadily taller as they produce leaves along a vertical stem. The leaves come in many different shapes and colours - some are finely pinnate to provide a greater surface area for gas exchange under water, while others look similar to the leaves of terrestrial plants. Many aquatic stem plants grow different leaf shapes depending on whether the plant is growing above or below the waterline. 

Our guide on non-aquatic plants have many comparison pictures of aquatic plants in their submerged form vs their emersed form.

Stem plants come in a huge variety of colours and shapes. Mastering stem plants opens the doors to a huge variety of possible plants to use in your aquarium.

Growth patterns of stem plants

Most stem plants grow continuously upwards from the apical bud. This allows the plant to grow tall and gain an advantage over other shorter plants by growing closer to the light and shading its competitors. In aquatic plants, this growth strategy also allows the plant to eventually break through the waterline, giving it access to surface air. These are huge competitive advantages - perhaps this is why so many aquatic species are stem plants.

Stem plants grow continuously both vertically and often outwards. Here the slower growing red Xyris plant is in danger of being shaded by the faster growing stem plant bushes around it.

The disadvantage of using stem plants in the aquarium is that many of them are fast and aggressive growers with little limit to the maximum height they can reach - most species will reach the top of hobbyist size aquariums given enough time. The tall growth of stem plants also tends to shade surrounding species, stunting their growth if the tall stem plants are left untrimmed and unchecked. On the positive side, plant competition also affects algae - a tank with aggressive, fast-growing plants creates an environment hostile to algae growth, and such densely planted tanks tend to be very resistant to algae.

Stem plants suffer from self-shading and overcrowding in fast growing tanks, leading to deterioration of the lower parts of the plant. From a layout perspective, fast-growing stem plants also change the appearance of the aquarium. For all these reasons, growing aquatic stem plants is a unique challenge for aquascapers. Many aquascapers who focus on hardscape will avoid using stem plants altogether due to the difficulty of managing them.

Basic propagation

All stem plant species can be easily propagated by cutting off the top few centimetres of a stem plant and planting it directly into the substrate. New buds and roots will grow from the internodes. Buried internodes will naturally send out roots. Mature stems that have already produced side shoots can also be cut off and replanted when they are a few centimetres in size. Stem plants are some of the easiest plants to propagate.

Trimming stem plants

Trimming can be done in 2 main ways.

Straight trimming

The first is to cut off the entire top at once. This means shearing off the entire top couple/few centimetres and leaving the lower rooted part to regrow fresh new tops. For this to be successful, the rooted part must be healthy enough to sprout new buds after cutting. This can be very counter-intuitive to newer aquarists as it seems that we are removing the most colourful and healthy top growth while leaving the less robust base parts of the stems.

In this example the Ludwigia arcuata is trimmed straight; the top 2 inches are cut off and the rooted base is left to sprout new shoots. Although the base may look very bad after trimming, it will recover within a few days and new shoots will emerge from the rooted base.

When pruning straight, the front row of plants should always be pruned shorter than the back row, creating a slope. This allows the stems to line up better for the front view. It is best to cut the front stems lower than the plants in front of them, so that the older part of the base is hidden; only the newer heads are visible when they grow above the front plants.

By removing the apical bud, this encourages lateral buds to develop along the stem at the internodes. This allows individual stems to branch and become more bushy. Factors that promote bushier growth and increased branching include - higher nutrient, CO2 and light levels. Healthier, faster growing plants are more likely to produce side shoots, whereas slower growing plants are more vertical and less branching. Branching is much more pronounced in CO2-injected aquariums.

Rotala florida on the left, Bacopa salzmannii SG on the right.

The white arrows above show lateral buds forming on the internodes of the main stem. These lateral buds can produce their own lateral buds as the bud matures. While many stem plants form lateral buds naturally when they are growing fast, many species only form more lateral buds when the apical bud has been cut.

Trimming by cutting off individual strands

The other method of trimming a stem plant bush is to pick out the longest individual strands of plants sticking out of the stem plant bush to even out the height of the bush as a whole. This technique is time consuming and requires some dexterity on the part of the aquascaper. The advantage of this technique is that if the stem plant bush is already in relatively good shape, it is not necessary to cut off the entire top of the bush. This technique preserves the shape of the bush while removing plant mass and giving the bush longevity before overcrowding sets in. Done skilfully, this can also reduce the height of the shrub or change its shape while retaining the aesthetic tops of most of the shrub.

More than 10 stems have been cut from the Rotala 'Blood Red SG' bush in the left picture, and the result (right) looks almost the same except that the plant mass has been reduced. This preserves the aesthetics of the aquarium for a longer period of time compared to straight pruning.

What species make good bushes?

Not all species can be easily shaped into pretty bushes. How extensively a plant branches depends very much on the species. Some species will not branch much and will never become a dense shrub, no matter how they are pruned. Species that branch easily and tolerate overcrowding are best suited to the straight pruning technique as they will regrow the canopy quickly and neatly. Species that do not branch much should be pruned by cutting off individual branches.

Examples of species that branch very readily:

Stem species that branch profusely after the apical bud has been cut off include: from left to right above - Pogostemon erectus, Rotala rotundifolia [and its many variants], Ludwigia arcuata and Myriophyllum golden [and other variants]. These species recover easily from straight pruning and form dense bushes. They are great for creating volume in the middle and back of the border. Other good species for dense shrubs are Hemianthus glomeratus (Pearlweed) and Limnophila aromatica. All plants on this page were grown with APT Complete in the water column and APT Jazz in the substrate.

Rotala rotundifolia (and its many cultivars) is one of the most popular background plants in the planted aquarium hobby due to its ability to be easily shaped into dense bushes. Rotala 'blood red SG' above takes pruning well and forms dense bushes with repeated pruning.

Ludwigia 'super red' and Ludwigia arcuata make great bushes and can be trimmed to contour around hardscape. Notice how steeply the plants are sloped (picture below) to give the nice frontal view (picture above).

Examples of species that branch loosely:

Some examples of loosely branching stem plants are: from left to right above - Bacopa caroliniana/colorata, Rotala macrandra [and its many variants, the variegated version is shown here], Rotala ramosior 'Florida' and Ludwigia senegalensis. These plants can make good bushes, but they are best used in the middle of the tank rather than in the background. There will be more gaps in the bush and you may need a larger clump of them to get a nice bush. However, with good pruning they will still make very nice bushes.

Examples of species that branch sparsely:

Some examples of stem plants that do not branch much are: from left to right above - Ludwigia pantanal/meta, Proserpinaca palustris, Ludwigia glandulosa, Persicaria 'sao paulo'. When the apical bud is cut off, only a few side shoots are formed along the internodes, and the distance between the side shoots is much greater than in the other examples mentioned above. Therefore, these species do not naturally form dense bushes when pruned straight. They can be forced into a dense clump by planting individual stems very close together, but none of these species take overcrowding well. These species are best used in the middle of the ground or in large groups to give the appearance of density. They are best pruned by picking off individual stems or replanting the tops each time.

Ludwigia pantanal/Meta grows long stems that do not branch much. Individual stems can be planted close together to create a denser grouping.

Self-shading and over-crowding

Leaves generally do not last forever - stem plants will continue to produce new leaves as the stem continues to grow towards more favourable areas (towards the light or to break through the waterline to reach the air), older leaves will deteriorate if shaded/overcrowded and no longer contribute to the overall growth of the plant. Different species have different tolerances to overcrowding. Some species have leaves that are very resilient and can tolerate long periods of overcrowding or shading, while other species will suffer very rapid deterioration of the lower stems when shaded/overcrowded.

Unstable or stressful conditions in the tank will greatly speed up the deterioration of lower stems.

For example, it is very common to see bare lower stems in non CO2-injected tanks due to the stress of maintaining plant mass in a low CO2 environment. Repeated straight trimming cycles also cause the lower parts of the stems to deteriorate more quickly.

Providing good light levels and good growth parameters (sufficient nutrients/CO2) can delay this deterioration, but most stem plants will experience it at some point. In order to keep the stems in good condition in the long term, replanting the tops is a necessity and unavoidable.

The mini macrandra type 4 has good looking top growth, but the bottoms have started to deteriorate. This is normal when stem plant shrubs get old and happens to different species at different rates.

Replanting tops

To refresh stem plant bushes, we will replant the fresh tops of the plants, while discarding the older bottom portions. Stem plants generally take very well to frequent replanting, compared to other types of plants. Most species regrow their root system readily.

The first step is to uproot the entire stem plant bush. To control the mess when pulling up the soil, we recommend using a water siphon to vacuum the area when pulling up plants. The siphon should be held very close to the point where the plant is being pulled up to catch the soil debris.

We will try to remove as much of the old root system as possible and also remove any organic debris that has accumulated in the area. While organic debris contributes small amounts of nutrients through decomposition, a build-up of organic debris will interfere with root formation for more delicate plants and will also trigger algae. To stir up the organic debris, we use a turkey baster to spray jets of water onto the substrate while vacuuming with a siphon. The aquasoil should look clean before we start replanting.

The next step is to sort the uprooted stems and select only the healthiest heads for replanting. If the substrate is low in nutrients, we will add root tabs to the replanting site to refresh the aquasoil. If you have followed the above steps, it will be just like planting fresh plants in a new tank - except that these plants will be able to skip the acclimation period because they have been taken from the same tank. By following the above steps, stem plant bushes can be kept in good condition for a long time.

This tank is over a year old, but looks as fresh as a newly planted tank. All the stem plant bushes and even the carpet have been replanted several times. Replanting fresh growth also makes the tank very resistant to algae, as fresh leaves on healthy plants are naturally resistant to algae.

Which tops to replant? and other details:

When replanting, the right section matters. Above, we have three Myriophyllum guyana cuttings. A is older and less robust- observe the darker, stiffer, knobby stem. B is younger and more robust, but has several branches, which will give rise to uneven new shoots. C is ideal. A single, younger, healthy stem. It is also thicker than A and B.

Another example, using the Rotala macrandra mini type IV green. A is a middle portion and already has several branches. It is a poor choice as it will give rise to very uneven growth. B is a weak cutting- observe how thin the stem is, and the lack of colour. If replanted, it has a lower chance of success. C is ideal. A thick, singular healthy top with healthy new leaves.

Above: Myriophyllum guyana replanted the 2Hr Way. Observe the even spacing and the use of healthy single-shoots. Also notice how clean the substrate is.

Above: Rotala 'blood red SG' after trimming. When the bottom stems are so bare, we recommend replanting the tops, instead of straight trimming. This species is so hardy that in this instance, the tops have a good chance of regrowing - however, it may not grow to the ideal density and growth form.

When replanting:

• Choose the thickest, single stems.
• Avoid branches, older stems or portions with algae.
• Clean the substrate surface thoroughly before replanting.
• Plant evenly with space around each stem.
• Cleanliness is key.

Refreshing old layouts

Replanting stem plant bushes may seem tedious at first, but it also offers a good opportunity to change the tank's layout over time. The pictures below are all of the same tank across 2+ years. Most of the base species were maintained but moved around, and the stem plant bushes were replanted quite a few times. Between the trimming cycles and replanting opportunities, a stem plant focused tank is ever-changing, with never a dull moment.

All tanks and plants on this page were grown with APT Complete in the water column and APT Jazz in the substrate.