AQUATIC HORTICULTURE		BY KAREN RANDALL

KAREN RANDALL

For a planted tank to remain a beautiful garden as opposed to a weed-choked jungle, the plants must be pruned and divided on a regular basis.

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

Rosette plants have a number of different strategies for reproduction. Many produce “offsets,” which are small plants that develop at the base of the parent plant. These can be removed by uprooting the entire plant and either removing the small plant by hand or with a sharp knife. Others reproduce by runner. The runners can be cut and the young plants moved to a new location if desired. It is important not to let runner plants get too dense or they will begin to choke each other, as well as other species. The pygmy chain sword (Echinodorus tenellus) is notorious in this regard. For a stand to remain healthy, it must be thinned regularly.

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.

Many swordplants reproduce by the formation of flower scapes. If these long “stalks” are allowed to emerge from the water, they will often produce flowers. In the wild, the plants would reproduce sexually in this state. In the aquarium, this is usually not practical. Fortunately, this same flower scape is also capable of producing plantlets. This almost always occurs if the scape is not allowed to emerge from the water and sometimes occurs even on emersed stalks. Some species produce large numbers of plantlets on the same stalk. You will produce fewer, but larger and healthier, young plants if you pinch off all but five or six plantlets on the stalk.

As soon as the plantlets have attained enough size and a sufficient root system, they can be removed from the stalk and planted directly in the substrate. Remember, however, that they are small and easily out-competed by larger plants. Make sure they have the light and elbowroom they need to grow.

Rhizome plants like Anubias, Java ferns and Bolbitis rarely need pruning per se, but they will need to have older dead or damaged leaves removed from time to time. It is usually easiest to do this with a pair of sharp scissors. When a stand becomes too large, it can be divided any place along the rhizome with a sharp knife or scissors. Just make sure that each section of rhizome has at least a few leaves and a healthy group of roots. Anubias can be encouraged to branch along the rhizome by slightly nicking the outside covering of the rhizome with your fingernail or a knife.

Java ferns have two other reproductive strategies. One of these is frequently seen under aquarium conditions, the other takes place almost exclusively in the wild. As Java fern leaves age, they often produce baby plantlets at the leaf margins. Like Echinodorus plantlets, as soon as they have achieved sufficient size, they can be removed and treated as you would an adult plant. It is frequently seen that a Java fern that is stressed will produce many very small plantlets in an effort to reproduce before it dies. This can be used to advantage should you desire to produce a great many young plants at once. Simply clip a leaf and allow it to float free in the tank. Before long, the entire leaf margin will be covered with tiny plantlets that can be nurtured into full-size plants with time and good care.

The evenly spaced brown spots often seen on the back of Java fern leaves are not a sign of disease. They are sporangia. In emersed form in the wild, the sporangia would open up and the wind would distribute the spores to new places to be populated by baby Java ferns.

Most bulb, tuber and corm plants are more challenging to propagate. Some lotus plants will develop small corms near the parent plant. With good conditions and a lot of time, these can eventually grow to adulthood. This is also true of some Crinum species.

Many Aponogeton can also be propagated in the aquarium. One species, A. undulatus, produces baby plantlets on a stalk, just like Echinodorus species. Instead of a tuber, A. rigidifolius grows on a rhizome and produces new plants along this rhizome as time goes by. Many of the other Aponogeton are the best candidates of any for sexual reproduction in the aquarium. Many flower freely even in a closed aquarium if there is even a little air space under the glass. Of these, many (although not all) are self-fertile.

To pollinate a self-fertile Aponogeton, simply run a Q-tip, a small paint brush or your finger back and forth over the flower spike in order to spread the pollen from flower to flower. Before long, you will see the fruits developing. The flower spike will begin to look more like a narrow green corn cob. Eventually, the stalk will begin to rot and the seeds will drop off. They will settle to the bottom of the aquarium. Here, unless they are disturbed by fish or the aquarist, they will sprout and develop into tiny new plants. If the substrate is rich and the light sufficient, these will be able to grow to adulthood.

If you want to maximize the production of new plantlets, it is best to move the seed head to a separate small aquarium with excellent growing conditions when the stalk begins to deteriorate. The seed head can just be left to float on top of this new tank until the seeds drop off. The seeds can also be collected from the main aquarium by enclosing the pollinated flower spike in a fine mesh bag (like a piece of nylon stocking) until the seeds develop. For best results, keep the water level in the nursery tank low until the plants are growing well. Then raise the height of the water as the plants grow so that they always remain submerged.

Finally remember that even in cool climates, mother nature can help with propagation during the summer months. Some plants that are slow to propagate under aquarium conditions reproduce at an amazing rate if moved outdoors into shallow containers containing soil substrates covered with coarse sand. Aquarium plants must be slowly acclimated to full sun conditions. They must be “hardened off” just like terrestrial seedlings. Place the containers in a shady location to start with, and slowly expose them to more and more sunlight. Some plants like Java ferns seem to always do better if kept in a shady location outdoors. Remember that even a shady location outdoors has more light than the average home aquarium!