House Plants and Hydroponics

All the methods of cultivation of house plants discussed so far are based on the traditional technique of planting them in compost and watering them regularly. Compost is the source of nutrients that, dissolved in water, are taken up by the plants through their roots. After a while, all the nutrients in the compost are used up, so it becomes necessary to give regular applications of feed. Providing a nutrient solution and adequate light are the two major aspects of house plant care (there is always ample carbon dioxide available naturally). Hydroponics – the method of growing plants in a nutrient solution – is based on this simple idea.

The plant is grown in a solution of tried-and-tested composition, which may be regulated by changing the proportions of the individual ingredients. Hydroponics is a ‘clean’ method of growing plants, eliminating the need for mixtures and fertilizers. At the same time, it decreases the danger of infection from diseases or infestation by pests that may exist in the soil. This method of soilless cultivation is particularly advantageous during prolonged absences from home (holidays, business trips and so on) because there is no need to water the plants.

Two containers are used: an inner and an outer one. Their size depends on the size of the plants. The outer container is a decorative one, but its colours should not be too bright. This contains the nutrient solution. The inner container, which has a perforated bottom, has a physiological function. The plant’s roots grow through the holes in the bottom and absorb nutrients from the solution.

Before putting plants in a hydroponic container, wash the roots with lukewarm water to remove all particles of soil. Also, remove all dead roots, taking care not to damage the healthy ones. First fill the container with clean water; rainwater is best. After about two weeks (not sooner) replace this with half-strength nutrient solution. Full-strength solution should only be used once the plants have put out their roots.

Sterile and chemically inert mineral substances are used to support the plants and to ensure that air can reach the roots; these do not provide any nourishment. It is important to use the correct size granules for this purpose. Granules measuring 3-20 mm are a suitable size. Smaller granules render the substrate impermeable to air and larger ones cause it to dry out quickly. Its chemical reaction must be neutral so that it does not affect the composition of the nutrient solution. It must not be too heavy and the granules must not be sharp or they might damage the plants. For low-growing or trailing plants, a fine and light substrate suffices; for large plants such as Philodendron, Sansevieria, Aglaonema, Dieffenbachia and Ficus, it should have a greater specific weight to ensure the plant’s stability. River sand or gravel, clinker, fireclay, perlite and ceramic granules are most commonly used as a substrate.

You can use tap water, rainwater or distilled water. Nutrient salts are then added. A carefully researched formula, in tablet or powder form, is available from most nurseries and garden suppliers. The formula has been worked out so that the salts can be used for all house plants suitable for soilless cultivation. It is important to top up the solution regularly. Plants absorb the water more rapidly than they absorb the nutrients, so, as the solution decreases in volume, it becomes more concentrated. Therefore, it is necessary to add water more frequently than nutrients. Top up the water about once a week in summer and add nutrients every two to three weeks.

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