ACS Distance Education UK
Hydroponics involves growing plants without soil. It doesn’t matter whether a plant is growing in the soil or in hydroponics: either way, it still needs essentially the same things to cause and control its survival and growth.
Two main factors influence the growth of a plant:
Genetic characteristics are diverse and varied, even within a species. They will give the plant a certain potential to grow and produce, but the environmental factors must also be just right for the plant’s full genetic potential to be realised.
All plants need appropriate conditions for growth in both the aerial environment and in the root environment.
Important aerial environment factors are:
Important root environment factors are:
Quantitatively and qualitatively, different plant varieties need different things. There is no such thing as an Ideal Environment for Hydroponic Growing because every plant cultivar has a different combination of ideal requirements.
The ideal nutrient levels for one plant may be totally inappropriate for another plant. One plant may prefer most of the roots to be almost immersed in water, these roots requiring very little oxygen; while another plant variety may need much less water, and far more oxygen around the roots.
Roots absorb nutrients, water and gasses, transmitting these ‘chemicals’ to feed other parts of the plant. Roots hold the plant in position and stop it from falling over or blowing away.
When we grow a plant in hydroponics, we must make sure that nutrients, water and oxygen are still supplied and that the plant is supported, as would occur if it was growing in soil.
Nutrient supply in soil is a more complex matter than in hydroponics due to the ability of soils to bind mineral elements, the presence of organic compounds and microbial action on these.
The main stem and its branches are the framework that supports the leaves, flowers and fruits. The leaves, and also green stems, manufacture food by the process known as photosynthesis, and this is transported to the flowers, fruits and roots. The vascular system within the stem consists of canals, or vessels, called the `xylem and phloem’ which transfer nutrients and water upwards and downwards through the plant.
The primary function of leaves is photosynthesis, a process in which light energy is caught from the sun and along with carbon dioxide from the air, produces assimilate in the form of carbohydrates such as sugars which can be stored or used for growth. The energy can then be retrieved and used in an essential process known as respiration. Leaves are also the principle plant part involved in the process known as transpiration whereby water evaporating, mainly through leaf pores (or stomata), sometimes through the leaf surface (or cuticle) as well, passes out of the leaf into a drier external environment. This evaporating water helps regulate the temperature of the plant. Transpiration also acts to pull water and calcium up from the root system through the xylem vessels.
The process of water evaporating from the leaves is very important in that it creates a water gradient or potential between the upper and lower parts of the plant. As the water evaporates from the plant cells in the leaves then more water is drawn from neighbouring cells to replace the lost water. Water is then drawn into those neighbouring cells from their neighbours and from conducting vessels in the stems. This process continues, eventually drawing water into the roots from the ground until the water gradient has been sufficiently reduced. As the water moves throughout the plant it carries nutrients, hormones, enzymes, etc. In effect this passage of water through the plant has a similar effect to a water pump, in this case causing water to be drawn from the ground, through the plant, and eventually out into the atmosphere.
Almost all plants grown in hydroponics are flowering plants, although many vegetable plants are not grown through to the flowering stage. These reproduce by pollen (i.e. male parts) fertilising an egg (i.e. female part found in the ovary of a flower). The ovary then grows to produce a fruit and the fertilised egg(s) will grow to produce seed.
There can sometimes be difficulty in obtaining a good crop because insufficient pollen, or non-viable reaches the female parts, resulting in insufficient fruit forming.