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Plant Biology and Requirements

Plant Biology

There are many different plant species and classes in the world, we are going to focus on the vegetables, herbs, flowers and fruit which make up the basis of the push into sustainable urban gardening and the ‘Grow Your Own’ initiative.

Plants can be looked at in terms of having 3 distinct and important sections, each with their own essential functions. These are:

Stems and branches

The leaves perform 3 extremely important functions for the plant, the manufacture of food through photosynthesis, respiration and transpiration. Respiration refers to the exchange of gases, taking in CO2 and releasing O2, this process is essential in photosynthesis and also puts oxygen into the air for other species to breathe. Similarly, transpiration is the loss of water through the leaf’s surface. As well as enabling CO2 to be taken up through the stomata the process enables water and minerals to move from the roots, through the stems, to the leaves. The most widely known process performed by a plant’s leaves in photosynthesis. It is the transformation of CO2, water and light energy into sugars which the plant then uses as fuel in all its other processes.

The basic functions of the stem is as a supporting structure for the plant and to transport food and water throughout the plant. These various transport highways are very complex and have no less than 6 individual parts which can be seen in the this diagram.

The function of the roots are to anchor the plant to the soil, as the main source of minerals and water to be transported to the stem and leaves and to also act as storage vessels for starches. Roots that can store maximum energy will provide the biggest and healthiest plants throughout their life. The health and size of a plant’s root mass will be reflected in the above ground plant. Ensuring the best possible base for your garden through good aeration, providing beneficial micro-organisms (trichoderma) and sufficient available minerals will result in a great garden you can enjoy with the whole family.

Plant Requirements

Plants have 3 basic requirements for growth:

Light (for photosynthesis)

Different plants need different amounts of each of these. Some plants thrive when they have high levels of light (eg cacti) while plants from deep underneath rainforest canopies (eg orchids) prefer indirect sources or low light conditions.

We all know that plants require food, which they can get from the soil or fertilisers that we add to the soil or the water. Just what is the food your plants need to grow and be healthy. Nutrients are divided into 2 main parts:


The macronutrients required by your plants are nitrogen, phosphorous and potassium. As the name suggests these elements are the ones used most by plants and are needed in abundant supply to ensure healthy and vigorous growth.

Micronutrients are broken down into 2 sub-sections governed by their requirement. The secondary nutrients include magnesium, sulphur and calcium and these are also required in large amounts by plants. The rest of the minerals required form the trace elements which include iron, zinc manganese, copper, boron, molybdenum, chlorine and silicon. These are only required in very small quantities but are none the less essential for healthy growth. More detailed information on each of these minerals and their significance can be found in our table
Nutrients and their functions.

Carbon dioxide (CO2) is used by plants during photosynthesis to make sugars which are essential for many growth related functions within the plant. In plants, photosynthesis is mainly carried out through the leaves where the stomata (small pores) take in the CO2 required. Photosynthesis also requires light and water to take place. The water is obtained through the roots and delivered to the leaves through the vascular tissue system. The sunlight is absorbed by chlorophyll, which is the green pigment that gives many plants their colour. Photosynthesis also consists of a dark stage reaction. This is when the plant converts the CO2 and energy (from the light cycle) to make the sugars required for growth.