AQUATIC HORTICULTURE		BY KAREN RANDALL

KAREN RANDALL

Stem plants, such as this Hygrophila polysperma, can be trimmed by cutting anywhere along the stem and replanting the cut pieces. H. polysperma tends to branch more and moore as it is trimmed, giving it a nice bushy appearance in a big tank like this.

Pruning, Dividing and Propagating in the Display Aquarium — Part One

The saying, “it’s a jungle out there,” is certainly apt for the planted tank. Left on its own, a single species of plant will become dominant in such a small space, choking out less-aggressive plants. Sooner or later, the tank would become a monoculture. In some instances, a monoculture is desirable or at least acceptable. If you are using plants simply to improve conditions for the sake of the fish in the tank or to provide fry cover, a monoculture-type tank is an easy to maintain alternative. You start with something that grows well for you and stick with it. Many breeders use Java moss (Vesicularia dubyana) and/or water sprite (Ceratopteris sp.) as their mainstays for these purposes. The fact that the plants add to the decorative value of the aquarium is a secondary consideration.

Another time when a monoculture can be considered is when working with some of the more difficult Cryptocoryne species. Many of these plants do far better when they do not have to compete with more aggressive neighbors for nutrients and root space.

Do you have questions, want to discuss the issues raised in this column, or read the comments of other aquarists and the answers from columnist Karen Randall? You can do so by going to Aquatic Interactive.

But for the average aquatic garden, a monoculture is not desirable. It is the juxtaposition of varied shapes and colors of foliage that make a planted display tank so appealing. To reach this end, the aquarist must become the selective “herbivore” needed to maintain balance among the plants in the system. We carefully see to it that prize specimens are not choked out, while removing sometimes vast quantities of more prolific species.

Floating plants are some of the most prolific reproducers in the planted aquarium. They have their good qualities — they provide needed shade and are very good at nutrient removal. They also provide excellent fry cover and spawning media for some species of fish. Unfortunately, they are sometimes too much of a good thing. They should not be allowed to cover the water in a planted tank, as they will block too much light from the plants below. Try to keep at least two-thirds of the surface of your tank free of floating plants unless you are purposely using them as fry protection or as algae control on a temporary basis.

The easiest way to deal with the smaller floaters, such as duckweed (Lemna minor), Azolla and Riccia, is to scoop the excess out with a net on a weekly basis during regular tank maintenance. Salvinia is, in my opinion, an easier floater to deal with because it is a little larger than the previously mentioned plants. It is easy to remove most of the Salvinia in a tank just by scooping it with your hand.

Bladderwort (Utricularia) is a little more of a nuisance. Because it will intertwine itself among any fine-leafed plants near the surface, it must be manually picked out and removed. While Java moss doesn’t float at the surface, it too can become a nuisance if it infests low-growing foreground plants, such as Lilaeopsis. I find that most of it can be harvested by carefully raking my fingers through the Lilaeopsis and removing the strands as I encounter them. If this is done regularly, the Java moss will be kept enough in check that it neither harms the other plants, nor disturbs the look of the aquascape.

One interesting side note about Utricularia. Takashi Amano uses the binding quality of this plant to hold together his submersed Riccia beds. Some aquarists are using Java moss in the same manner.

Hornwort (Ceratophyllum) is a plant that is often used as fry cover in fish tanks. I personally don’t think it is very useful in a carefully planned aquatic garden. If you do use it, the stems should be regularly snipped to manageable lengths. The growing tips of hornwort are usually the more attractive parts, so if you have lots, you may want to keep these and toss the other end. Large floating water sprites should also be kept in check, but I like to make sure I leave at least a few small plantlets of this useful genus in one tank or another in case I need them.

There are two acceptable methods of pruning stem plants. Some look best if the entire plant is pulled up when it gets too large, discarding the bottom part of the stems and replanting the tops. This method is best for stem plants that do not branch much, as well as those that tend to develop scraggly, unattractive lower stems. Examples would be Bacopa and Rotala. This is also the best approach for those “fluffy” stem plants that look prettiest with long unbranched stems, such as Cabomba and Limnophila species.

Other plants get bushier and more attractive if they are pinched back hard. These plants, like many terrestrials, will branch more every time they are pinched back. Hygrophila and Ludwigia are two larger leafed examples of plants that do well with this treatment. There are many small-leafed types that benefit from this treatment too. Hemianthus micranthemoides, Micranthemum umbrosum and Didiplis diandra are species that come immediately to mind. Amano advocates an even more aggressive treatment for these plants. He gives them a “haircut” straight across, several inches above the substrate, to encourage even bushier growth.

To propagate most stem plants, simply take cuttings and insert them in the substrate. They will quickly develop roots and you are in business. There are some stem plants that don’t branch well until they can actually lay across the surface of the water. Rotala macrandra is a good example of a plant with this growth pattern. You will be able to propagate the plant much more quickly if you allow this habit and trim stems intermittently after they have spread across the surface.

Most rosette plants cannot be “pruned” like a stem plant. With Vallisneria and Sagittaria, some people trim the ends of the leaves if they lay across the water surface and block light. The disadvantage of this method of trimming is that the damaged end of the leaf often begins to rot. Eventually, the whole leaf will die back. The best answer is to use those species that will not outgrow the height of the tank they are kept in. Alternatively, it is preferable to remove the longer outside leaves while allowing the shorter, young inner leaves to grow rather than to damage the leaves by shortening them.

Vallisneria, Sagittaria, Cryptocoryne and some Echinodorus species spread by runner, just below the surface of the substrate. A healthy bed of Vallisneria will need regular thinning or it will begin to take over the tank. Large, older plants can be thinned from the middle of the bed by feeling around them to find the attached runners and severing them as you slowly work the plant out of the group. Removing young plants from edges of the stand is easier. These can just be pulled up — roots, runners and all — and pinched from the parent stand at any convenient point.

Over a period of time (usually a least a couple of years), many of these plants will spread to the point that the substrate becomes completely root-bound. Besides the competition for light and nutrients caused by this crowding, the root systems of the plants will pull too much oxygen down into the substrate, causing many nutrients to be held in a state not easily accessed by the plants. At this point, the aquarist often notices that the growth of the plants slows down markedly. Once this happens, it is often best to pull up the entire stand, break the runners apart and replant the area with a smaller number of plants. As long as conditions in the tank are good and the substrate has not been exhausted, the plants should quickly recover their old vigor.

In the case of Cryptocoryne species, the aquarist must carefully weigh the possible benefits of breaking apart the stand against the strong possibility that the whole stand will “melt” in response to a major environmental change. If you decide you must disturb a stand of crypts, it is best to divide the group into large sections containing a number of plants, rather than dividing them into individual specimens. Moved as an entire group, they stand a much better chance of weathering the upheaval intact. Remember, though, that even if your stand does melt, it may very well recover if left undisturbed in a tank with good conditions. While it is possible to harvest young plants and runners from some species of Cryptocoryne with impunity, use caution with the more delicate species. Some will respond to the removal of even a single plant by going into a decline.