Printer Friendly

Materials for Plant Growth

Clarification Statement: Emphasis is on the idea that plant matter comes mostly from air and water, not from soil.

Ocean Literacy Principles:


What do Plants Need to Grow?

Plants can grow in a wide variety of environments, from deserts to rainforests, within fresh and salt water, and high on mountain tops and low in the valleys. There is a huge diversity of plants, from tiny microscopic algae, called phytoplankton, to the giant banyan trees (Fig. 1A & 1B). Without the array of plants, life on Earth would not exist as we know it.

<p>FIg. 1A. Phytoplankton are microscopic plants that live in bodies of water and are the base of many food webs.&nbsp;</p><br />
<p>Fig. 1B.&nbsp;Banyan trees, like this one found in Honolulu, can reach enormous sizes.</p><br />

<p>Fig. 2. Photosynthesis stores energy, fixes carbon into energy-rich carbon-hydrogen bonds, forms plant matter, releases oxygen, and maintains plants’ activities.</p>

How is it possible that these plants can survive in different conditions? It's simple - plants get the materials they need to grow cheifly from air and water. Sunlight provides the energy needed to convert water and carbon dioxide (CO2), a major component in air, to carbohydrates, such as sugars, in a process called photosynthesis (Fig. 2). Plants can then use these sugars to build and grow new material. So, where there is air, water, and sunlight, there can be plants!


Most plants we see are in soil, but it is not necessary for growth. Soil often provides structure, retains water, and gives extra nutrients, however all of these benefits can be added to hydroponic systems.

What is Hydroponics?

Hydroponics is a method of growing plants without soil. In hydroponic systems, nutrient enriched waters are delivered directly to plant roots. Although most plants grow in soil, the soil itself is not necessary to plant growth. It is the nutrients within the soil that the plants need. In addition to nutrients, plants need water, sunlight, and carbon dioxide. Plants get carbon dioxide mainly from the air (and water if they are aquatic plants). This means that the biomass, or volume and weight of plants and trees, also comes chiefly from the air!

Hydroponic Systems

The term hydroponics comes from the latin root words hydro and ponos, meaning water and labor. Water does the work to deliver the nutrients to plants instead of soil! There are many different types of hydroponic systems— with a range of complexity and expense. As long as the water can be circulated throughout the roots, the plant will be able to grow (Fig. 2).

Examples of some systems are:

  • Vertically hanging with roots exposed to water spray/flow (Fig. 3).
  • Series of pipes, with roots submerged in highly oxygenated and nutrient enriched water.
  • Use of root supports other than soil that allow for consistent water flow. For example cinder, coconut husks, vermiculite, or gravel.

<p>Fig. 2. Hydroponic systems make it possible for larde scale production of food with less wasted space and water.</p> <p>Fig. 3. Vertical hydroponic systems allow for more growth opportunity in smaller spaces.&nbsp;</p><br />

Water Conditions

To grow plants hydroponically, it  is important to maintain proper nutrient levels. It is also important to ensure the pH is balanced. For small scale systems, using pre-mixed plant food is the easiest way to ensure the correct balance of nutrients. The pH is the measure of how acidic or alkaline a solution is (Fig. 3). The pH affects the plants ability to take up the essential nutrients. Generally, the optimum range of pH for plants grown hydroponically is between 5.5 and 6.5, but this may vary across plant species. For more information on the ideal pH of a nutrient solition, refer to resources such as Perfecting the pH of your Hydroponic Nutrient Solition

<p>Fig. 5. The pH scale compares the acidty or alkalinity of various solutions.</p><br />

Hydroponics Vocabulary

  • Acidic: A substance having the properties of an acid, with a pH below 7
  • Alkaline: A substance having the properties of an alkali, with a pH greater than 7.
  • Carbohydrate: an organic compounds occurring in foods and living tissues and including sugars, starch, and cellulose.
  • Carbon Dioxide (CO2): A colorless, odorless gas made of one carbon atom and two oxygen atoms covalently bonded together. CO2 is produced by plants and animals during cellular respiration. CO2 is also producedby burning carbon and organic compounds. CO2 is naturally present in air and is absorbed by plants during photosynthesis.
  • Hydroponics: a method for growing plants in water without using soil.
  • pH scale: a scale used to express the acidity or alkalinity based on the number of hydrogen ions in a solution. On the pH scale of 1-14, 7 is neutral; lower values are more acid and higher values more alkaline. (Note: The pH scale is logarithmic, so the distance between values is not linear. pH also depends on temperature.)
  • Photosynthesis: the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water
  • Phytoplankton: plankton consisting of microscopic plants

Table of Contents:

Representative Image: 
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.