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Messy aerial roots?
"Aerial roots are roots that often grow out of the internodes of stem plants midway up the stem, above the substrate.
Why do these roots appear? Are they a cause for concern? What can we do if we find them unsightly?
Territorial Instinct
Aerial roots are most common in sparse tanks or where there is a lot of space around the stem plants. In such environments, aerial roots develop naturally to support territorial expansion.
If they successfully root into the substrate, new stems can develop from the internodes.
In the top picture above, a cutting of Rotala 'Blood Red' was placed as a single stem in a corner of the tank. It had plenty of space around it and began to branch and develop aerial roots.
Compare this with the same cuttings planted in a denser bush. In the 'bush' setting, the cuttings concentrated on growing upwards (to reach the light), had less branching and much less aerial root development.
Propagation Instinct
In general, when stem plants start to grow horizontally, often at the surface of the tank, the natural response is for serial roots to start to grow. In nature, this prepares the plant to colonise other areas when it is swept away by currents.
Branching Instinct
Aerial roots are usually associated with side shoots or branches. In many ways, the side shoot is a completely separate plant. When we prune (rather than replant) the tops of stem plants, this encourages side shoots (and therefore aerial roots) to grow. So over-pruning often results in an abundance of aerial roots.
Substrate Confusion
Coarse substrate (such as pea gravel or pebbles) or poor quality substrate can confuse the plants as to where the substrate really is. This can cause aerial roots to sprout in internodes lower down the stem before the stem has gained significant height. The plant is looking for a place to root but does not recognise the substrate as soil due to the large grain size or poor substrate quality.
Under-nutrition
Apart from the above examples, aerial roots can also occur in undernourished plants, where excessive roots are produced as the plant diverts more energy to nutrient-seeking functions. However, in such cases the plant would often show other signs of poor nutrient access: smaller or poorly formed leaves.
If you find them unsightly, you can take the following actions:
- Plant in denser clumps. This works for stem plants that take crowding well (Rotala rotundifolia and its variants, Ludwig arcuata etc.)
- Instead of simply trimming tall stem plants, replant the tops and discard the old stems and roots. This is routinely done for most Dutch Style Aquascapes.
- Trim plants before they get too close to the surface. Near the surface, stem plants will usually bend or grow sideways. They would start to branch and aerial roots will almost always develop.
- Use finer substrate. This is especially the case for carpets.
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