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February 18, 2025 3 min read
“Will it help rejuvenate my overgrown tank?”
Yes, but not in a way you might be thinking.
Aquatic plants are not perennial.
They are not like trees where you prune and new leaves regrow again and again.
In particular, as stem plants grow taller, the lower portions become shaded and begin to deteriorate naturally. The rate of decay depends on a few key factors, primarily plant species, growth rate, light intensity, substrate nutrition, and overall plant health. In the picture above, the Ludwig Pantanal bush took about 6 weeks to reach this state. The tops (not shown) have reached the water surface. Note the sparse shaded stems, the aerial roots, and the poor condition of the old leaves at the bottom.
Above: If we cut off the top of Ludwig's Pantanal above, the new shoots that emerge are likely to be small and weak. Stems that are too decayed may not produce new shoots at all.
This is because aquatic plants are constantly discarding old growth and redirecting their energy into new leaves. In other words, it is wrong to discard new growth. Instead, we discard the old stems and roots (yes, the roots) and replant the healthy tops. New roots will soon sprout. This is especially true for stem plants, which make up 90% of commercially available aquatic plants.
But I see people trim their stem plants?
Oh yes, it is okay to prune once, twice, even three times. But even plants that take well to pruning (Rotala rotundifolia, for example) would need to be replanted after months of natural deterioration of the lower stems. Many stem plants do not take well to pruning and should ideally be replanted each time they grow tall - Syngonanthus species, for example.
Above: Stem plants like Limnophila aromatica above can quickly become dense bushes. This causes the lower parts to become shaded. If denied light, these parts will naturally deteriorate over time. Some species are very resilient and can regrow from bare stems (e.g. Limnophila aromatica, Staurogyne repens). However, the vast majority of species will do better if the fresh tops are replanted.
Healthy tops are easy to replant. It may feel traumatizing to cut and discard the plant's old stem and roots, but the plant prefers it. Fresh roots sprout easily and happily from healthy tops. Better nutrition also helps extend the life of the plant. Growing plants a little more slowly than at breakneck speed lengthens replanting cycles. It makes maintenance easier - you need to replant less often.
Old leaves do not rejuvenate.
Improved conditions show up in new growth, not old leaves.
This is especially true for stem crops and fast-growing species.
When they get better nutrition, 90% of that boost goes to new growth. For leaves that are still basically healthy, the rate of deterioration may slow and the leaf may even improve. This is especially true for slow growing species such as Anubias and Bucephalandra where some regeneration may occur. But for most stem plants (and stem plants make up 90% of the plants commonly sold in aquarium stores), the older leaves will not regenerate.
The picture above illustrates this point. We are transferring a Variegated Rotala macrandra from the store to a 2HR tank. In the shop, the leaves are greener and the internodes are longer due to lower light and inadequate fertilization. After being transferred to a 2HR tank, the newly produced leaves are completely red, reflecting the higher light and better fertilization. Note, however, that the old leaves grown in the shop will not rejuvenate.
It is common for new plants in a new tank to struggle at the beginning.
They may get a bout of nasty algae, as shown on the S. Repens above.
Most gardeners are happy when things finally settle down.
Counterintuitively, the best thing to do then is to cut, discard old stems, leaves and roots, and replant the healthy tops. This is especially true for stems. The older stems and leaves that were grown in the store or damaged by algae during the initial planting will not heal, as shown above. And roots will grow quickly from healthy tops.
So prepare to replant new plants:)