The daily pleasures of gardening are simple, inexpensive and profoundly satisfying. But in the ever-increasingly dense and sprawling cities, gardening on rooftops, patios and balconies is the only way to transform them into liveable spaces that are lush, productive and purifying.
Imagine picking a head of lettuce that was cultivated in your rooftop, or taking in the morning perfume of a flower in your balcony, or biting into a strawberry warmed by the sun….
Although, many of us in cities nurture this dream but gardening is a very time consuming activity and due to our fast paced and busy lifestyles there is not enough time in our daily lives to realize this dream.
Rooftop gardening through hydroponic technique is a veritable way of life and enables you to take pleasure in new, green spaces that meet the needs for relaxation and leisure.
Imagine growing a vegetable garden without having to fight the soil. No more worries about too much water; or too little water; or how much fertilizer; or when to fertilize; or the labours of cultivating and weeding to provide just the right soil consistency and texture; and how much space to give each plant to avoid competing for food and water; etc.
There are many advantages of growing plants hydroponically:
- Hydroponic gardens produce the healthiest crops with high yields and are consistently reliable
- Gardening is clean and extremely easy, requiring very little effort
- Due to nutrients fed directly to the roots, plants grow faster and with small roots plants may be grown closer. In general hydroponically grown garden needs 1/5 of the overall space when compared with soil gardens
- Hydroponically grown plants do not come in contact with soil borne pests and diseases thus saves costs of soil preparation, insecticides and fungicides.
Since the amount of nutrient solution is fed directly to the plant roots, there is no wastage of water due to run off or evaporation
Overall, the main advantages of hydroponics over soil culture are – more efficient nutrition regulation, availability in regions of the world having no arable land, efficient use of water and fertilizers, ease and low cost of sterilization of the medium, and higher density planting, leading to increased yields per acre.
What is Hydroponics?
Plants are Nature’s greatest factories. Powered by light from the sun, plants combine the earth’s most basic chemical elements with water and gases in the air to create food and energy for growth.
Water is the basis of life; every living plant depends on it to thrive. In nature, water acts to recharge the soil with nutrients. When it rains, lifeless plant and animal matter decay. Microorganisms, insects and animals hasten this process by their consumption of plants and excretion of organic wastes. Organic wastes in the soil are biologically decomposed into the basic nutrient salts that plants feed on.
In Hydroponics, this natural process is bypassed by providing these basic nutrient salts in a balanced solution form directly to the plant roots. Hydroponics is about enriching water with the very same nutrient salts as found in nature. It is about creating and maintaining a “nutrient solution” that is perfectly balanced for your plants..
Soil and Plant Interrelations
Soil provides four needs to the plant; 1) A supply of water 2) Supply of essential nutrients 3) Supply of Oxygen 4) Support for the plant root system. Optimum soil composition must be 25% water, 25% air, 45% mineral matter and 5% organic matter. The soil water is held within the soil pores and together with its dissolved salts makes up the soil solution which is very important as a medium for supplying nutrients to the growing plants
Plant rootlets and root hairs are in intimate contact with the soil colloids (particles) present in the soil solution. Ions are exchanged between the soil colloids and the soil solution. Nutrient uptake by the plants’ roots takes place at the surface of the soil colloids surfaces and through the soil solution proper. Ions are interchanged between the soil colloids and the soil solution. Movement of ions takes place between the plant root surfaces and soil colloids and also between the plant root surfaces and soil solution.
The soil solution is the most important source of nutrients for absorption by plant roots. Since it is very dilute, as the plants deplete the nutrients from the soil solution. It must be relished by the soil particles (colloids). The solid phase of soil releases mineral elements into the soil solution partly by solubilisation of soil minerals and organic matter, partly by solution of soluble salts, and partly by cation exchange
Soil versus Hydroponics
There is no physiological difference between plants grown plants grown hydroponically and those grown in soil. In soil both organic and inorganic components must be broken into inorganic elements, such as calcium, magnesium, potassium, phosphorus, iron etc. before they are available to plants. These elements adhere to the soil particles and are exchanged into the soil solution where they are absorbed by the plants.
In Hydroponics the plant roots are moistened with the nutrient solution containing these elements. The subsequent mineral uptake by plants is the same (depicted in green color in the chart)
Soil Free Hydroponic Mediums
In hydroponics, soil free mediums are used for starting seeds and providing support to the plant. Plant roots need both air and water and so a perfect medium is one that is able to hold a nearly equal concentration of air and water. The determining factor in water/air holding capacity of a medium is the small spaces between each granule or fiber.
There are many types of sterile substances with varying water/air holding capacities which can be used as a medium. Most common media types are – Coco peat, Perlite, Expanded clay pellets, Rockwool. You could also use sand, gravel, saw dust, sponge as grow media.
Coco Peat: Our favorite loose growing medium is Coconut Fiber or Coco peat. It represents a major step forward in organic soil free potting mediums. It has the water retention of vermiculite and the air retention of perlite. It is a completely organic medium made from coconut husks.
Ground up and sterilized coco peat offers plants the perfect rooting medium and protection against root diseases and fungus infestation. Coco peat is a completely renewable resource, unlike peat moss which is rapidly becoming depleted from overuse.
Perlite: Perlite has been around for the longest time of all these soil free mediums. It is made from air-puffed glass pellets, and literally as light as air.
To understand nutrient formulations in hydroponics, we must know the organic composition of plants and elements available in the atmosphere and soil.
90% of all organic matter on Earth comprises of Carbon, Hydrogen and Oxygen. Our planet’s atmosphere contains 78% Nitrogen, 20% Oxygen and 2% Carbon dioxide, in addition to a small percentage of inert gases.
There are 16 elements which are considered to be essential for growth of higher plants. 3 of these elements -Carbon, Hydrogen and Oxygen are absorbed from the atmosphere. The remaining 13 elements are classified as macronutrients (required in large quantities) and micronutrients (required in small quantities)
Plants possess the ability to extract Carbon, Hydrogen, and Oxygen from the atmosphere in the presence of macro and micronutrients to create food. Light provides the energy to make this possible. This process of creating food using light is called photosynthesis
Essential Elements for most higher plants and their function
The following table shows the various types of chemical elements needed by the plants and their functions for healthy growth.
Composition of Nutrient Solutions (ppm)
Nutrient formulations are usually given in parts per million (ppm) concentration of each essential element. One ppm is one part of one item in one million parts of another. For example 250 ppm of calcium in a solution can be 250 microgram per gram or 250 milligram per litre.
Optimum nutrient requirement of plants depends on various factors – Plant species and variety, stage of plant growth, season of the year and the weather. Requirements, particularly of Nitrogen, Phosphorus and Potassium vary with plant type and stage of growth. Lettuce and other leafy vegetables need higher levels of nitrogen than tomatoes and cucumbers. The latter two requires higher rates of phosphorus, calcium and potassium.
Some of the complete hydroponic Nutrient Formulations (Composition of elements in ppm) is shown in the table below:
List of commonly available Fertilizer Salts
In hydroponics all the essential elements are supplied to the plants by dissolving fertilizer salts in water to make the nutrient solution. The choice of salts to be used depends on a number of factors such as solubility in water, cost, availability and most importantly to satisfy the ppm requirement of all elements without excessive supply. For example one molecule of potassium nitrate (KNO3) will yield one ion of potassium (K+) and one ion of nitrate, whereas one molecule of calcium nitrate (Ca(NO3)2) will yield 1 ion of calcium (Ca++) and 2 ions of nitrate 2(NO3-). Therefore, if a minimum number of cations is wanted while supplying sufficient nitrate (anions) then calcium nitrate should be used.
The following table shows commonly available fertilizer salts from which the elements needed (table above) can be supplied to plants in required quantities:
Nutrient Solution Preparation
If you remember high school chemistry, you will find this section easy to understand.
Atomic and molecular weights of elements and compounds must be used in calculating nutrient formulation and concentration requirements. Please refer the previous table – Commonly avaliable fertilizer salts, The molecular weight of Ca(NO3)2 is 164.1 (This molecule contains 1 atom of calcium, 2 atoms of nitrogen and 6 atoms of Oxygen). Atomic weights of Calcium – 40, Nitrogen – 14 and Oxygen – 16. So, Mol. wt of Ca(NO3)2 is 40+(2×14)+(6×16)=164.
Now, if a nutrient formulation calls for 200 ppm of calcium (i.e 200 mg per litre) we need 200 mg of calcium in every litre of water. We know that in 164 mg of Ca(NO3)2 we have 40 mg of calcium, so first step in calculation is to find out how much of Ca(NO3)2 is needed to supply 200 mg of calcium.
164 mg of Ca(NO3)2 = 40 mg of Ca
“X” mg of Ca(NO3)2 = 200 mg of Ca
X = 164 x 200/ 40 =>820 mg
820 mg of Ca(NO3)2 will supply 200 mg of Calcium
Since, calcium nitrate contains nitrogen also, 820 mg of calcium nitrate contains (820/164) x 28 => 140 mg of Nitrogen is already supplied while fulfiling the callcium requirement. If the formulation requires 160 mg of Nitrogen, we are short of 20 mg. This can be supplied by KNO3 while fulfilling the potassium reguirement.
This is an iterative process which goes on till the time all the nutrient requirements are met with the available salts.
You could follow these steps – Calcium should be provided by calcium nitrate. Calcium nitrate will also provide nitrate nitrogen. Any additional nitrogen required should be provided by potassium nitrate, which also provides some potassium. All the phosphorus may be obtained from monopotassium phosphate, which also provides some potassium. The remaining potassium requirement can be obtained from potassium sulphate, which also provides some sulphur. Additional sulphur comes from other sulphates such as magnesium sulphate, which is used to supply magnesium needs.