Hydroponics
What Plants Need.
Hydroponics is possible because plants do not need soil to grow. However, they do need other things – light, air, water, warmth, nutrients, and support. Hydroponics systems and any other growing systems for plants must supply these.
Light
Light is a form of energy. Plants use this energy in a process called photosynthesis (a natural process that uses light, carbon dioxide, and water to make carbohydrates for the plant).
During Photosynthesis the energy from light is used to change carbon dioxide and water into carbohydrates (sugar and starches) and oxygen. There will also be some leftover water. The oxygen and water are released into the air. Perhaps the best example of this is a terrarium (an enclosed glass container used to grow plants) where the released oxygen and water are released into the air of the closed container.
Some of the carbohydrates are used for plant processes such as growth. Others are stored. Later the stored carbohydrates may be used as food by the plant or by the animal or person who eats the plant.
Air
You’ve read that photosynthesis requires energy, water, and carbon dioxide. Carbon dioxide is a colorless gas that consists of the elements carbon and oxygen. Plants get the carbon dioxide they need from the air. It enters the plant through small openings in the leaves called stomata.
Water
Plants need water to carry out their life processes, such as growth. Water is also important as a way for nutrient to reach the plant.
Plants absorb water through their roots. Much of that water escapes through the leaves’ stomata as water vapor. In order to stay healthy, plants need to replace this lost water.
If the air is dry, the plant will lose water faster. Most plants do better when the air is fairly humid (moist). In dry climates, plants have adapted to the lack of humidity. The “needles” of a cactus are its leaves. What would be the advantage of having such small, thin, leaves?
Outdoors, the amount of rainfall and humidity help determine what kinds of plants can be grown. When plants are grown in enclosed spaces, such as a greenhouse, the amount of water they receive and the humidity of the air can be controlled. It is possible, for example, to grow bananas in an Arizona greenhouse, though banana trees would not survive there outdoors.
Warmth
Some plants prefer hot weather, while others like it cooler; but no plants can grow in freezing temperatures. Most plants will grow well if the temperature is about 72 degrees Fahrenheit (22 degrees Celsius) during the day. They need lower temperatures at night, about 62 degrees Fahrenheit (17 Celsius).
Outdoors, the temperature will vary with the seasons and the time of the day. Indoors, temperature can be controlled.
Nutrients
Plants obtain 97 percent of the things they need from the air and water. The rest comes from chemicals dissolved in water. These chemicals are nutrients the plants use to grow, stay healthy, and reproduce. Scientists have identified many of these elements that plants need. The most important of these are nitrogen, phosphorus, and potassium.
Nutrients are present in soil, although the right kinds and amounts are not always there. Farmers test the soil and add nutrients (fertilizers) as needed. In a hydroponics system, there is no soil. The nutrients must therefore be added to the water.
pH Values
Many substances are acids. Common examples include vinegar and lemon juice. Bases are also common. Two examples are shampoo and laundry detergent. The pH value of a substance is a measure of how acidic or basic that substance is.
What does this have to do with plants? If the pH of the soil – or, in hydroponics, the pH of the nutrient solution – is too high or low, the plants will not be able to use the nutrients. Most plants do well when the pH value is between 5.6 and 6.5. In other words, they prefer a slightly acidic soil or solution. Farmers and gardeners measure pH to find out weather it is within the correct range. If it isn’t they adjust the pH by adding an acid or a base.
Support
Imagine a tree without roots. Even if the tree could survive, it couldn’t stay upright. It would fall. If it was a small tree, the wind might blow it over. Most plants need support – something that will help them stay in place.
In nature, most plants are supported by soil, which firmly holds the plants’ roots. If the plants are to be grown without soil, they need other support. In a hydroponics system, there are several ways to support it.
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