"A technique of growing plants in nutrient solution."

Hydroponics means literally 'water-working' or 'water-activation'. It is a soiless cultivation technique; plants grow in nutrient solution rather than in soil.

The nutrient solution and its management is the cornerstone for success in a hydroponics system. The function of a hydroponics nutrient solution is to supply the plants' roots with water, oxygen and essential mineral elements in soluble form.

There are 17 mineral elements that are generally essential for plant growth. Nine of these elements (macro nutrients): carbons, hydrogen, oxygen, sulphur, phosphorus, calcium, magnesium, potassium, and nitrogen are required in relatively large amounts. The remaining eight elements (micro nutrients or trace elements): iron, zinc, copper, manganese, boron, chlorine, cobalt and molybdenum are needed in only minute amounts.

Nutrient solution can be prepared using commercially available premixed chemicals or from inorganic fertilizer salts.

pH and Electrical Conductivity are the two primary parameters in nutrient solution control.

pH of nutrient solution

pH is a measurement of the hydrogen ion concentration in a particular medium, such as water, soil, etc. Simply put, it refers to the degree of acidity and alkalinity of that medium. It is measured in a logarithmic scale ranging from 0 to 14. A pH value of 7 is neutral, a pH value below 7 is acidic and a pH value above 7 is alkaline.

The pH of a nutrient solution or a medium is important for plant growth. Every plant species has a preferred pH range in which it will grow best. If a plant is subjected to a pH outside of its preferred range, retardation of growth and even death of the plant may result.
 
Very low and high pH values can affect plants in the following ways:
 
1. Extreme pH conditions such as very low pH (below pH 4.5) and very high pH conditions (above pH 9) can cause damage to plant roots directly.
      
2. The pH of the nutrient solution affects the solubility, in turn affecting the availability of certain elements as well, particularly that of micro nutrients. The majority of the nutrient elements are available at a pH range of 6 to 7.5. At very low or high pH conditions, some nutrients may be locked in the medium, causing them to become unavailable for plant growth. For example, high pH reduces the availability of iron, manganese, copper and zinc while low pH reduces the availability of potassium, sulphur, calcium, magnesium and phosphorus. At very low pH conditions, excessive uptake of toxic levels of manganese may result.
      
3. As the pH of some media are raised, more negative charges are produced on their colloidal surfaces, making them capable of holding and locking up more actions of the nutrient solution. The majority of hydroponics media are not affected this way as they are basically inert materials such as gravel and sand. However, media that contain clay or some of those derived from volcanic rocks can be affected.
 

pH Adjustments

For most hydroponics cropping, the pH of the nutrient solution should not be allowed to rise above 6.5 or to fall below 6. For pH adjustments, sodium hydroxide (NAOH) is the preferred alkali and hydrochloric acid (HCI) is the preferred acid.

However, for some plants, the pH of the nutrient solution is best allowed to seek its own level naturally. This is because some plant species are capable of reducing the pH of the nutrient solution in the immediate vicinity of their roots. This acidification enhances their ability to absorb certain elements such as iron. If the nutrient solution is constantly changed due to the use of inconsistent nutrient solution, it can interfere with the plant's natural ability to enhance its absorptive capability.

Trans Instrument's Horti-Care pH Check is designed for nutrient pH tests. It is rugged, water and drop-shock resistant. It is the ultimate pH pocket size meter.

 
Table: Optimum pH and Nutrient Concentration in EC / cF / TDS range for growth of some vegetable crops

Crops	EC	cF	pH	TDS
Asparagus	1.4 - 1.8	14 - 18	6.0 - 6.8	980 - 1,300
Broad Bean	1.8 - 2.2	18 - 22	6.0 - 6.5	1,300 - 1,500
Broccoli	2.8 - 3.0	28 - 30	6.5 - 7.0	2,000 - 2,500
Cabbage	2.5 - 3.0	25 - 30	6.5 - 7.0	1,800 - 2,100
Capsicum	2.0 - 2.5	20 - 25	6.0 - 6.5	1,400 - 1,800
Carrots	1.5 - 2.0	15 - 20	6.5	1,200 - 1,400
Cauliflower	1.5 - 2.0	15 - 20	6.5 - 7.0	1,200 - 1,400
Celery	2.0 - 2.5	20 - 25	6.5	1,400 - 1,800
Cucumber	2.0 - 2.5	20 - 25	5.5	1,400 - 1,800
Eggplant	2.5 - 3.5	25 - 35	6.0	1,800 - 2,500
Garlic	1.4 - 1.8	14 - 18	6.0	980 - 1,300
Lettuces	1.0 - 1.5	10 - 15	6.0 - 7.0	700 - 1,100

Electo-Conductivity (EC)

The concentration of the nutrient elements in a nutrient solution can be estimated by measuring the ability of the nutrient solution to conduct an electric current. This is because the quantity of dissolved solids in the nutrient solution is directly proportional to the conductivity. When there is a greater concentration of nutrients, the current will flow faster and when there is a lower concentration, the current will flow slower. Thus, by measuring the conductivity, one can determine how strong or weak a nutrient solution is.

Conductivity is generally measured at 25 °C. A rise in temperature or a drop in temperature will result in a corresponding rise or drop in conductivity even though no extra nutrient elements are added. It is possible to correct the conductivity data to standard temperature of 25 °C by multiplying the conductivity by a temperature conversion factor (see table below).

Table: Temperature conversion factors for correcting conductivity data to standard temperature of 25 °C
 

Temperature (°C)	Conversion factor
15	1.247
20	1.112
22	1.064
25	1.000
25	0.960
30	0.907

We have developed pocket size meters: Horti-Care Nutrient Check, specially for measuring the electrical conductivity of nutrient solutions. All readings are automatically temperature compensated. You do not need to do any calculation or conversion. All you have to do is to immerse the meter's sensor into the nutrient solution and read the readings directly.

For commercial farmers and specialist growers with the need of intenstive testing and good reliability, the HortiStick 3-in-1 is the perfect tool for measuring all the three important parameters for nutrient solutions: pH, Nutrient Concentrations and Temperature.

Lighting for Plants

Light is a necessity for plant growth. Sufficient light is needed for photosynthesis to take place so that plants can flower or even bare fruit.

Houseplants have become popular as indoor decorations. Attractive and refreshing, they break the monotony of a room and bring back a little nature indoors. However, a chosen spot to locate a plant for decoration may not be ideal for plant growth. Lack of adequate light is the most common cause of plants turning yellow and having poor growth. Supplementary electrical lighting is the easiest and least expensive way to provide enough light for the plants. As all artificial lighting will degrade in intensity with time, it is essential to measure the lighting with the Horti-LiteCheck tester at regular intervals to tell if replacements are required.
 
GENERAL PLANT LIGHTING PREFERENCE: (Readings here only serve as a guide)

LOW LIGHT PLANTS 500 to 2,500 Lux 50 to 250 fc	MEDIUM LIGHT PLANTS 2,500 to 19,000 Lux 250 to 1,900 fc	HIGH LIGHT PLANTS 19,000 Lux above 1,900 fc above
Aluminum Plant, Pilea cadierei. Arrowhead vine, Syngonium podophyllum. Cast iron plant, Aspidistra elatior. Chinese evergreen, Aglaonema modestum. Jade plant, Crassula argentea.	African violet, Saintpaulia species Cissus species: Grape ivy, Cissus rhombifolia, Kangaroo vine, Cissus antarctica. Dieffenbachia, dumbcane. Flame violet, Episcia capreata varieties. Ficus species: Rubber plant, Ficus elastica varieties, Weeping fig, Ficus benjamina. Gloxinia, Sinningia speciosa fifyana varieties. Impatiens, sultana, Impatiens walleriana holstii.	Cacti and succulents. Aucuba-Leaf croton, Codiaeum 'Aucubaeolium'. Herbs. Orange: Dwarf or Calamondin, Citrus mitis.

2,500 to 19,000 Lux 250 to 1,900 fc

5,000 to 19,000 Lux above 500 to 1,900 fc above

Asparagus ferns, Asparagus densiflorus 'Sprengeri'. Asparagus setaceus. Ferns: Birdsnest fern, Asplenium nidus, Boston fern, Cyrtomium falcatum, Maidenhair fern. Adiantum species. Sansevieria, snake plant, Sanseveria trifasciata. Spathiphyllum, 'Clevelandii'. Spider plant, airplane plant, Chlorophytum comosum 'Vittatum'. Swedish ivy, Plectranthus australis. Wandering jew, Tradescantia fluminensis, Zebrina pendula.

Hoya: Hindu rope plant, Hoya carnosa 'Hummels compacta', Wax plant, Hoya carnosa. Ivy, Hedera helix varieties. Schefflera, umbrella tree, Brassaia actinophylla.