Most people have heard of photosynthesis, if only for use as an answer on quiz programmes.   For gardeners though it is interesting to know a little of the science behind the only process that enables us to store and use energy from the sun. No photosynthesis, no food, no fossil fuel, not even carbon neutral bio-mass. Photosynthesis also takes in carbon dioxide and puts out oxygen keeping the air we breathe in balance. So green plants and photosynthesis are vital for life on earth. Gardeners do not need a full chemical explanation of photosynthesis but a simple grasp of the key elements will help you keep your garden green.

Green chlorophyll within the leaves absorbs light from the sun, but light energy is unstable so it is quickly converted into electrical energy that is then ‘fixed’ in the form of glucose.  Glucose fuels plant growth and any excess may be stored for future use inthe  roots or bulbs. The conversion uses Carbon from atmospheric carbon dioxide (CO₂), and Hydrogen from soil water (H₂O) taken in through plant roots.  The process releases the left over Oxygen back into the atmosphere. For those of you with a scientific disposition the formula is : CO₂ + + H₂O + energy -> C₆H1₂O₆ + O₂

Photosynthesis can be limited by lack if light – plants in the shade collect less sunlight than those in a bright position and temperature – all checmical reactions slow doewn in lower tmperatures and speed up in higher temperatures so leaves photosynthesise less on cold days and as we get into winter. Finally water is the key source of Hydrogen and if a plant is suffering even 10% dehydration then photosynthesis may reduce by up to 70|%.

Variegated plants – either specially bred or a natural sport – are generally less vigorous then the green species as they contain less chlorophyll to capture energy for growth.  This is a useful rule to remember when selecting plants.  For example if you want to keep ivy under control on a fence, choose a variegated form; not only is it more decorative it will need less cutting back.