General Principles for the Cultivation of Aquatic Plants

In order to give aquarium plants a perfectly suitable medium, we must first be aware of the conditions existing in their native habitat. Most aquarium plants come from tropical and subtropical areas, with a few from the warmer parts of the temperate zone. Often the aquarist will see in print or hear in discussions the assumption that tropical soils are fertile and rich in nutrients; this is of course in error. As a rule the soil in the tropics is poor because

Aerial view of Rio Purus, a tributary of the Amazon River, taken during the dry part of the year. Note the great scouring effect of water currents on the banks. Photo by Dr. H.R. Axelrod,

Anna Maria Island HistoryWater Hyacinth Roots

Root system of the water hyacinth (Eichbornia crassipes). Photo by Dr. D Sculthorpe.

great quantities of organic substances, arising from defoliation and by the death of tropical vegetation, are consumed by the soil organisms so quickly that the decomposition of this material is faster than the rate at which it is replaced. High temperatures and high humidity make possible such a quick decomposition or mineralization of organic substances that the tropical soil is poorer in nutrients than ordinary field soil in temperate climates.

Plants in their natural environments are continually damaged by animals and by weather conditions such as floods. They grow in water that for at least part of the growing period is muddy and full of impurities that settle on the leaves and impede the functioning of the plants. The bottom of tropical pools and streams is often peaty, and peat is of course a very poor source of nutrients.

In the aquarium we cannot adhere to all these natural conditions because in a confined habitat they are obviously detrimental to the plants. Instead we prepare a much better medium which has many of the advantages of the natural environment without its disadvantages.

Unlike most land plants, aquatic plants are not dependent solely on nutrition obtained through the root system. They are able to receive nutrients through the whole surface of the plant body, especially the epidermis of the leaves. Such typically submersed plants as Ceratophyllum and Utricularia do not form roots at all, while Elodea and Najas form only very short ones. For this reason the composition of not only the soil but of the water is of great importance, as the water must contain many mineral substances ab-

The leaves of the bladderwort (Utricularia) are modified into small bladders capable of ingesting minute organisms like Daphnia but not fish fry. Blad-derworts do not develop roots.

The leaves of the bladderwort (Utricularia) are modified into small bladders capable of ingesting minute organisms like Daphnia but not fish fry. Blad-derworts do not develop roots.

sorbed directly by the plant. This must be taken into consideration when establishing an aquarium and selecting the planting medium.

There has long been a controversy over whether such rooted submersed plants as Cryptocoryne and Echinodorus receive the majority of their nutrients through the leaves or the roots. Either answer is partially correct, as the method of absorption varies with different concentrations of nutrients in the medium. As a general rule, the more diluted the solution, the more accessible the minerals. If there is a very heavy concentration of nutrients in the soil, only the small percentage dissolved in the water will actually be available to the plant.

Occasionally aquarists have good luck growing plants for several months or longer when using such normally objectionable bottom materials as peat, garden soil, industrial fertilizer, or clay. This is because we are never really quite certain about the proper -

The elongated tubers of the underwater banana plant (Nymphoides aqua-tica) contain reserve food material. Photo by Dr. D. Sculthorpe.

The elongated tubers of the underwater banana plant (Nymphoides aqua-tica) contain reserve food material. Photo by Dr. D. Sculthorpe.

Gory Death Photos
Plants of various species and origin can be combined artistically in a single tank provided their requirements do not conflict.

ties of the substrate just from its name. It is necessary to determine many factors, such as the pH, the proportions of the major nutrients (nitrates, phosphates, etc.), the presence or absence of certain important microelements, the amount of humus, etc. Not many aquarists are able to test for all this necessary information without access to a well equipped laboratory. Commercial soil testing kits are available for some of the substrate components, but not for all.

The safest and most uniform method of setting up the planted aquarium is to start off with plain washed sand or gravel and for the first year or so use only plants with strong and well developed rhizomes. The rhizomes should have enough stored food reserves to last the plant at least several months. Good starting plants include the stronger species of Echinodorus, Cryptocoryne, Lagenandra, Aponogeton, and Crinum, In a newly established aquarium we cannot grow such plants as Myriophyllum, Ludwigia, or Cabom-ba, as these lack reserve food supplies.

Start the aquarium by purchasing good quality rather coarse sand from a reputable dealer. Make sure the sand is washed clean of all impurities. On the bottom of the aquarium install a good quality undergravel filter to ensure the circulation of the oxygenated water through the sand and around the roots of the plants. This speeds the decomposition of organic substances such as fish feces and food remains to the mineral state and provides a constant temperature throughout the aquarium. By using a sand substrate together with an undergravel filter we can be confident that the water will not contain a surplus of organic substances and will be supplied with sufficient mineral nutrients necessary for the good development of the plants.

To obtain maximum growth and longevity from your plants, the undergravel filter should preferably be the type consisting of numerous small perforated plastic tubes. With this type of filter there is no gap between the base of the aquarium and the sand bed. Thus there is no place for debris to build up where it cannot be decomposed by the proper bacteria in the presence of oxygen. The tube-type filter also has less chance of getting tangled in the growing roots of the plants.

For the first year the substrate is poor in nutrients, but with the passing of time it becomes richer and richer due to the accumulation and decomposition of fish and plant wastes. The type of fish kept can to some extent determine how fast nutrients accumulate, as some fish are naturally "dirtier" than others. Thus most of the live-bearers, including the swordtails, platies, mollies, and gup-pies, produce dirtier and richer bottoms than the tetrad of similar size. In the normal aquarium there is plenty of detritus, usually more than necessary for the plants. It must on occasion be cleaned out, as only the detritus under the surface of the sand is really necessary for the plants to obtain sufficient nutrients. An aquarium two or three years old is an ideal environment for the growth and development of all species of aquatic plants.

It is important that the detritus in the sand should be decomposed in the presence of oxygen. This decomposition, called aerobic, does not occur when the substrate medium is air-tight. Airtight media include such things as peat, clay, and garden soil. Anaerobic decomposition (decomposition in the absence of air) results in the formation of poisonous gases such as hydrogen sulphide. These gases appear as bubbles which leak out of the bottom when the plants are pulled out; the roots will be brown or black. Hydrogen sulphide can destroy both plants and fish. Industrial fer-

Diy Undergravel

Inexpensive type of undergravel filter with a continuous base of perforated plastic material.

This undergravel filter consists of a series of parallel rows of perforated plastic tubes. Photo courtesy Eureka Products Company.

Plants Aquarium Amazon River

A small fish population can provide the plants in an aquarium with enough nutrients so that the addition of fertilizers is truly unnecessary.

tilizers are a source of hydrogen sulphide, so they should not be used in the aquarium. Fish produce enough nutrients for the plants.

When we talk of a poor substrate or a medium which has to be supplied with nutrients, we do not mean a base without any compounds or with added fertilizers or soil; we are simply referring to an aquarium with a substrate formed of clean, washed sand. A planting medium in a newly established tank or in an aquarium with a small number of fish is poor. It is moderately rich to rich when composed of washed sand in an established tank containing a reasonable number of fish for a period of six to eight months.

Readers should not be influenced by various publications and pictures illustrating tiny plants grown in clean sand and giant plants growing in fertilized soil or industrial nutrients. How would such pictures look when taken one, two, or three years laterP By then the influence of anaerobic decomposition and poisonous gases will have become obvious. If you do not believe this, just check the aquariums of the professionals who acclimatize newly imported plants—you will find only clean, washed sand, never soil or fertilizers.

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Aquarium and Fish Care Tactics

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