My stem plant is losing lower leaves, what is wrong?

From time to time we get a worried 'Oh no! What have I done wrong?' email with a picture of a plant that looks like the one above (a bouquet of Lobelia cardinalis after 4 months).

Actually, nothing is wrong.

Aquatic plants, unlike some terrestrial woody species, are not perennial. They are more like herbs, which require regular re-propagation. For aquatic plants, this means regularly cutting and replanting the healthy tops.

Above: Cutting and replanting healthy tops is necessary for all aquatic plants, especially stem plants. The 5 steps would be:

1. Cut the top 4- 5 inches of healthy tops.
2. Pull out and discard all old stems and roots.
3. Enrich substrate.
4. Replant healthy tops.
5. Water Change the 2Hr Way to remove stirred up detritus.

Of the 5 steps above, step 3 is often neglected. Depleted substrate will result in thinner and weaker plants over time. You can enrich the substrate by mixing in new Aquasoil, or use something like APT Jazz.

It is important to note that simply adding iron or trace minerals will not help. The element that is naturally depleted over time and has the greatest effect is nitrogen. Nitrates do not naturally remain bound in the substrate (they are water soluble and quickly leach into the water, depleting the substrate). So using a root fertiliser that retains nitrogen in the substrate is key.

 Step 5 is also often neglected and is the cause of many algae problems. After replanting, always make sure you vacuum up any floating debris. The tank water should be crystal clear after a proper Water Change the 2Hr Way.

With regularly enriched substrate and regular replanting, you can keep Lobelia cardinalis looking like the bouquet above 'forever'. For lower maintenance, rhizomes (vs stem plants) like Java Fern (below) are good options.

Old leaves can be simply trimmed and discarded. There is no need to regularly cut-and-replant. Java Fern would grow dense, and after many months it would be necessary to thin the bush, but it does not require cutting and replanting the same way that stem plants do.

You mean aquatic plants are not like trees?
Aquatic plants are more like herbs, where their natural lifecycle involves natural deterioration of lower stems and roots.

I can just replant the top...without roots?
New roots will sprout quickly and naturally.

When should I cut and replant?
Always cut and replant before the tips reach the water surface. Whenever lower shaded stems start to deteriorate, it is time to replant.

But I see people trimming, instead of cutting and replanting?
When bottom stems are healthy, you can trim once, twice, even 3 times. But after 3 trims, it is generally time to replant, even for the healthiest stem plants.

Isn't that alot of work?
Experienced aquarists would keep a mix of low maintenance (non-stem) plants and high-maintenance plants (stems are carpets). A tank that is mostly filled with stem-plants does require alot of maintenance!

This tank at the 2hr Aquarist gallery has been running for more than a year. This tank uses APT Complete and APT Jazz.

All of the stem plants have been topped and replanted a few times over the year. Planted tanks need to be constantly rejuvenated through trimming and replanting to look in good form. The enrichment of the substrate through APT Jazz root tabs means that the each cycle grows as though the aquasoil substrate is like new. Tanks can run in good form for many years without requiring complete resetting with these techniques.

Head over here to read more on how to maintain the aquasoil substrate long term

Head over here to read how trimming and replanting helps solve algae issues