Preventing damage, holes and algae on older leaves of aquatic plants

Why do old leaves deteriorate in the first place?

There are many factors that cause this, but the main reason in planted tanks is a change in environment that requires the plant to reprogramme its enzymes to make the best use of what is available in the current environment. For example, if you move a plant from shade to an area of very high light, the plant can divert energy from the production of light trapping pigments in its leaves to the production of new leaves or protective pigments instead. Green plants will grow deeper green in shade because they need to produce more chlorophyll to survive, while many red species will only grow very red in high light - because they produce protective pigments in high light.

While older leaves have some plasticity that allows them to adapt, there are limits to how much old leaves can adapt. Only leaves that started growing in the new environment can be fully optimised to take advantage of the current environmental conditions. If there are drastic changes in the environment, the plant may choose to focus its energy on producing new leaves, while abandoning its older leaves that are no longer suited to the new environment.

Plant stress caused by poor access to CO2 or nutrients also forces the plant to divert energy into new growth in an attempt to survive. For example, stem plants deprived of CO2 often drop their older leaves prematurely to divert energy to top growth in an attempt to break through the water surface and gain access to air.

Well-fed plants generally adapt better to changes in the aquarium environment because they have more stored energy. Macronutrients such as nitrogen, phosphate and potassium are mobile within the plant. Prolonged nutrient deficiency can force plants to use these nutrients from older leaves to support new growth. Therefore, plants grown under excessively low nutrient conditions may experience accelerated deterioration of older leaves as new leaves grow due to environmental changes.

Therefore, when buying plants in the shop, it is important to check that the plants are robust and well grown. Healthy, robust plants will have an easier time adapting when transferred to the aquarium.

Example of adaptation changes due to a change in environment

In this picture we have transferred a Variegated Rotala macrandra from the shop tank to ours. In the shop the leaves are greener and the internodes longer due to the lower light and inadequate fertilisation. After planting in our farm tank, the new leaves produced are fully red, reflecting the higher light and fertiliser levels. Note, however, that the old leaves grown in the shop have not produced this adaptation. They are programmed to make best use of what was available in the shop tank environment, not the new tank, and even an improvement in their new environment cannot fully change this. This is primarily because there is a significant difference in environment between the shop tank and our own tank.

After the plant has grown for some time in our farm tank, we cut off the top part, which has adapted to the tank, and replant it, discarding the bottom part (which was grown in the shop). The fully adapted plant retains its older leaves longer, and even the old growth is more resistant to algae. Notice that even the older leaves further down the stem are well coloured and in good condition because they are adapted to this tank;

If you have 100% adapted growth in a tank (adapted growth means that the part of the plant was grown under the current tank conditions), the tank as a whole will be much more resistant to algae. Therefore, replanting new growth and discarding old growth is one of the key actions that can make a tank more resistant to algae as a whole.

If the environment changes drastically and the old leaves that were programmed for a different environment cannot function well - the plant will channel all its energy into new growth, even drawing energy and nutrients from the old growth to feed the development of new leaves. This accelerates the decay of the old leaves. This is why plants bought in shops often lose their old leaves, even though they grow strong new ones.

Most plants classified as 'easy plants' have more plasticity and can adapt existing leaves to a wider range of new conditions. Finicky species that are classified as difficult to grow are often difficult because they have difficulty adapting to new conditions - many such species, once adapted, are actually quite undemanding plants. The prime example of a plant classified as difficult in this way is Utricularia gramminifolia. It's a total weed that isn't particularly demanding once established, but many aquarists have problems getting it to adapt to the aquarium environment.

Utricularia gramminifolia is not particularly demanding in terms of growth parameters. It will grow well in harder or softer water, with higher or lower nutrient levels, with high or low CO2 levels. However, it does require a stable, well-cycled aquarium to settle in and grow. Its difficult settling period has led to many myths about its growth requirements, when in fact it can grow in almost any tank as long as it is stable and well cycled.

Do damaged leaves heal?

Leaves do not have the ability to heal physical damage such as puncture holes or tears. Cells in the plant tissue will form a callus at the site of the wound to seal it, but the leaf itself will not fully regenerate. If the leaf is not too badly damaged, it can continue to function after the wound has been sealed. If the damage is severe, the plant will divert energy into producing new leaves instead, and the damaged leaf will deteriorate at an accelerated rate.

In mild cases of nutrient deficiency - for example, a lack of magnesium causing pale leaves - adding the missing nutrient may cause the whole plant to become greener. However, old, decaying leaves on a plant, especially when the leaf starts to show physical deterioration (such as fragmentation, holes or broken leaf edges), will not renew themselves even when conditions become favourable - the plant will instead channel energy into producing new leaves. In this way, plants continually renew themselves by producing new growth that is optimised for the current environmental conditions, while shedding older leaves.

This Bucephalandra leaf suffered physical damage, but do not show signs of significant deterioration otherwise. The leaf still functions normally, but one could trim it off for aesthetic reasons.

This Anubias leaf has deteriorated too much to be of any use. The plant draws nutrients from the decaying leaf and channels them into new growth. This accelerates the decay of the leaf and makes it a prime candidate for algae. Note how the algae only target the damaged leaf. Cutting it off would make room for new growth and prevent it from shading potential growth underneath.

What to do with damaged leaves ?

With stem plants, it is common for the plant to put most of its energy into new top growth, which is closer to the light and the current, while older leaves on the stem deteriorate. Spacing stem plants apart and allowing more light to reach the lower levels can reduce this effect somewhat. However, in many species the top shoots will naturally crowd out and shade the lower parts of the plant. Hardy species such as Rotala rotundifolia variants may not lose their lower leaves quickly, but for many other species the density of the top growth will cause the lower leaves to deteriorate.

During pruning cycles, the upper part of the healthy leaves should be cut and replanted, and the lower deteriorating part uprooted and discarded. This will rejuvenate the bush each cycle.

Due to shading and overcrowding, the lower leaves of this clump of Ludwigia senegalensis have deteriorated considerably. The whole plant should be uprooted, the robust top cut off and replanted, and the lower leaves discarded.

Some stem plants (such as the Ludwigia senegalensis shown here) are better left slightly apart, allowing some light and air to penetrate the bush. Other species can tolerate a bit of overcrowding and can be used to form denser bushes. (Lobelia cardinalis, Staurogyne repens, Limnophila vietnam etc). Tidiness and proper spacing should not be underestimated.

In the case of rhizome plants such as Anubias and Bucephalandra species, old, decaying leaves should be cut off. The bare rhizome itself may produce new leaves or shoot tips, and cutting off older, damaged leaves will make room for new growth. Overcrowded clumps should be separated into individual rhizomes if you want to maximise growth as a whole. Too many people are afraid to cut old growth from Bucephalandra - reducing overcrowding and making room for new growth will allow the clump to grow healthier and faster.

In this example, we would cut off all the older/damaged leaves circled in orange. This would make room for fresh new growth. Older, damaged growth is also more susceptible to algae; if you have a tank full of old growth, it will make your tank very susceptible to algae.

For rosette plants such as Crypts or Sword plants, cut off damaged leaves at the base. Removing decaying old leaves removes a spawning ground for algae.

Maintaining quality of older leaves

To maintain the health of old leaves, it is important to minimise shocks to the system; dips in CO2 supply are particularly stressful. Nutrient availability plays an important role; nutrient deficiencies can lead to premature decay of older leaves. A well balanced fertilisation regime in the water column is important, as is maintaining substrate richness if root feeding is used. Inconsistent nutrient dosing or major disturbances to the tank ecosystem (such as an ammonia spike) can also cause plant stress and hasten the deterioration of older leaves. These same factors also cause algae spores to bloom - often resulting in older leaves becoming covered with algae. Repeatedly moving plants that do not like to be moved, or allowing weaker species to be outcompeted by more aggressively growing species can also stress plants.

Slower growing species such as Bucephalandra are slow to adapt. If you consider that only new growth grown in the current tank conditions is fully optimised for the current tank, and combine this with how slowly Bucephalandra produce new leaves, full adaptation of Bucephalandra clumps will take months. With species like this you need very long term stability to grow large clumps of them well. This means applying good plant and tank management techniques not just for weeks, but for several months, with no significant break in routine in between.

If you change tank parameters or growth conditions every few weeks, fast-growing stem plants may be able to adapt, but your Bucephalandra, which only produces one new leaf a week, will never catch up. In unstable tanks there will always be holes or algae in the older leaves of the Bucephalandra. The key word here is consistency.

If you have persistent holes and algae on the older leaves in Bucephalandra, but feel that you have not tweaked CO2/light/nutrients much at all, chances are that either poor maintenance techniques have been used (failure to maintain low organic waste levels, poor horticultural techniques in trimming, replanting etc) or the system has been poorly set up (poor flow, too much flow, plant placement errors, poor choice of equipment etc).

Perhaps one of the species we are best known for is the Bucephalandra Brownie Ghost 2011. It is a slightly more finicky Bucephalandra species, and so makes for great feedback on whether you are doing things right or wrong over a long time horizon. We started with 3 rhizomes a couple of years ago and now have about 150 of them (and have sold/given away more than a hundred in between). The other species we are well known for is Hygrophila sp Chai - we also started with a single plant and now have a large patch of this as well.

The key to both species is not the ability to get both plants to grow new leaves - Bucephalandra has super low requirements, while Hygrophila sp Chai will grow if you throw enough light and CO2 at it - it's the ability to preserve the older leaves and not lose them to melt or algae. Maintaining the tank stability required to not lose the old growth requires a far more delicate and experienced hand than throwing a ton of light and CO2 at it to get new growth - something less experienced hobbyists quickly realise when they start growing these species.

A few key points on maintaining a stable tank

• Horticultural decisions play a big part. Make sure that each clump of plants has enough light, flow and space to meet its needs. Some plants can tolerate overcrowding (e.g. Rotala roundifolia, Staurogyne repens, Limnophila vietnam etc) while others do better with more space (e.g. Ludwigia pantanal, Proserpinaca palustris, Rotala butterfly etc). TLDR; plant spacing is very important for some species.

• Choose trimming methods that maximize healthy leaves - some species are better topped and replanted, discarding the older bottoms (such as Syngonanthus species, Ludwigia senegalensis, more picky Rotala macrandras) While others can be trimmed repeated (straight cutting off and discarding the tops) without issues as the bottom rooted portions regenerate new growth easily. (Limnophila aromatica, Staurogyne repens, Alternanthera reineckii, Rotala rotundifolia etc)

• Doing big resets of the tank due to over-crowding is more destabilizing than making small changes here and there. Develop the discipline to do meaningful weekly maintenance, and not wait till the system is on the brink of crashing to do something.

• Cleanliness is very important - this means regularly removing organic debris with large water changes (up to 100%), while at the same time removing larger organic particles from the substrate and foliage. However, ensure that your refill water parameters are not drastically different from your current tank water. Develop a system to make this task efficient (no buckets). If it is tedious, you may not be able to keep up in the long run.

• Fertilization should be regular. Most enthusiasts have no issue with water column dosing. However, very few folks know how to enrich and maintain their substrate long term. This is equally important if your tank is dependent on substrate feeding of plants.

• A fully planted tank is more resistant to algae for all the plants present. If you are growing species that are particularly susceptible to algae on older leaves, such as Hygrophila sp. chai, it is important to have an algae-resistant tank as a whole.

• Having reliable equipment is a big plus. Faulty CO2 equipment causing a 2 or 3 day dip in CO2 levels can crash high light high growth tanks pretty badly. 

• Having the right filter/flow setup at the start helps tremendously. This includes setting up adequate flow in the system (6-10X filter turnover) with a flow pattern that is neither too turbulent (which triggers BBA) or too weak (detritus on leaves lead to algae).

• Cooler tanks are inherently more stable and easier to manage because the metabolism of plants and algae is slower. Every degree above 26 degrees Celsius makes it more difficult. This is not to say that plants will not grow at higher temperatures - in fact most plants will grow faster due to their increased metabolism. However, algae can be difficult to manage. In warm tanks, aquarists need to be even more astute in other areas of maintenance.

• Observation and early detection of plant problems is important. Neat tanks allow better observation and organization. 

Many experienced aquarists space their plants neatly, and also vary their height so that aggressive growers do not crowd out and shade plants that require more light and current. Here the rock formations provide physical barriers that prevent taller stemmed plants from crowding out and shading the shorter, more delicate species. Tank by Jon Ooi