Home FAQ Hydroponics What influences plant growth ? 1. LIGHT 7. FRESH AIR BUT ABSENCE OF WIND 2. DARK 8. PRESENCE OF CARBON DIOXIDE GAS 3. WATER 9. NUTRIENT TEMPERATURE 4. NUTRIENTS 10. pH 5. WARMTH 11. IONISATION 6. SUPPORT 12. GENETIC MAKEUP

1. LIGHT
A minimum quality and quantity of light is required. The light is required for photosynthesis - the manufacture of proteins and sugars for the plant to grow. The light needs to be at the ultra-violet (blue) end of the spectrum so if growing indoors exclusively then special globes or lights are required.

2. DARK
A dark period every 24 hours is required so that the plant can stop photosynthesis and produce the sugars required for growth.

3. WATER
Good quality water is required for the plant to absorb for building proteins, sugars and new plant cells.

4. NUTRIENTS
Plants require macro and micro nutrients for the growth process ( see separate detailed list )

5. WARMTH
Photosynthesis will not occur except within the general temperature range of 5 and 45 degrees Celcius

6. SUPPORT
Most plants require support for either the root system or the stem or both.

7. FRESH AIR BUT ABSENCE OF WIND
Plant growth requires fresh air but very few plants thrive
in windy conditions.

8. PRESENCE OF CARBON DIOXIDE GAS
Plants are grouped into three main biological classifications as far as carbon dioxide fixation is concerned. - C3, C4, and CAM. These are the different types of bonding sites (receptor sites) for carbon dioxide.

Once the bonding process is complete a series of chemical reactions occur to break down the carbon dioxide and water to create carbohydrates. An enriched carbon dioxide atmosphere can give an increase in photosynthesis of between 30 and 60%. Increasing the carbon dioxide can also increase the water use efficiency - Under normal carbon dioxide atmospheric conditions carbon dioxide diffuses into the leaf while water travels up the root system and transpires through the stomata. In a carbon dioxide enriched environment the stomata shrink so that the plants transpire less water - they become more water efficient.

Normal concentration of carbon dioxide gas in the atmosphere is about 340 parts per million. Enrichment is usually aimed at producing 1300 to 1500 parts per million of carbon dioxide gas whilst the light intensity is about 40,000 lux (3800 footcandles with the temperature about 30 degree Celcius. ( levels above 2000 parts per million become toxic to the plant. )

Levels of carbon dioxide below 200 parts per million can cause some plants to stop growing.

9. NUTRIENT TEMPERATURE
Ideal water temperature for total solubility of the nutrient salts is 20 to 22 degrees Celcius.

10. pH
pH values above 7.5 cause iron, manganese, copper, zinc and boron ions to be less available to plants.

pH values below 6 cause the solubility of phosphoric acid, calcium and magnesium to drop.

pH values between 3 and 5 and temperatures above 26 degrees Celcius encourage the development of fungal diseases.

Diurnal variation of pH

Daylight photosynthesis produces hydrogen ions which can cause the nutrient acidity to increase (lowering the pH) At dusk photosynthesis stops and the plants increase their rate of respiration and this coupled with the respiration of micro organisms and the decomposition of organic matter uses up the hydrogen ions so the acidity of the solution tends to decrease ( pH rises ) Most varieties of vegetables grow at their best in a nutrient solution having a pH between 6.0 and 7.5 and a nutrient temperature between 20 and 22 degrees celcius

Low light (overcast days or indoor growing environments) - Plants take up more potassium and phosphorous from the
nutrient solution so the acidity increases (pH drops).

Strong intense light (clear sunny days)- Plants take up more nitrogen from the nutrient solution so the acidity decreases (pH rises).

11. IONISATION
An 'ion' is a molecule with an abnormal number of electrons. The air we breathe is a mixture of gas molecules mainly oxygen and nitrogen. The majority of these molecules are electrically neutral.

When an air molecule loses or gains an electron it becomes positively or negatively charged ion. This process goes on all the time so nature provides a constant supply of positive and negative ions. Fresh air contains more or less equal quantites of these ions.( about 2000 ions per cubic centimetre each).

Negative ions play an active role in cleaning the air of polution particles by electrostatic precipitation. Negative ions move faster than positive ions and quickly lose their electrons to dirt particles, water vapour, other air molecules or any surface they touch. In any enclosed volume of air such as a room negative ions tend to decrease whilst positive ions tend to remain much longer.

Ions of either charge help plant growth by speeding up the intake of iron and the production of iron-containing enzymes. High air ion concentrations stimulate the metabolism of adenosine triphosphate (ATP the high energy compound) and supplement both the nucleic acid metabolism and oxygen uptake. Negative ion generators are preferable where people are concerned. The negative ions will tend to remove pollutants from the air (reductions in dust, pollen and smells).

12. GENETIC MAKEUP
The genetic makeup of the plant's cells can play an important role in the overall growth performance of a plant. Plants can be selectively bred for certain desired characteristics. Tulips and Roses are a common example of breeding for colour and stem length. Early fruiting varieties of Tomatoes are grown to take advantage of market prices.

Plant growth is the result of all the above factors and their interactions.