Hydroponics is the science of growing plants without soil– although the plants may or may not be suspended in a solid medium such as gravel, or expanded clay balls.
Soil retains minerals and nutrients, which “feed” flora, as we all know. Plant roots can’t absorb dirt, however; when water passes through soil, it dissolves and collects some of the nutrient particles embedded. This “food” solution is absorbable as a liquid. As you can see, the soil itself is not an integral part of a plant’s feeding cycle — it is simply a stabilizer for the roots, and a convenient filter.
Why eliminate the soil?
Plants breathe air, just like humans. School children are taught a simple lesson: plants take in carbon dioxide, and release oxygen. The entire plant — not just leafy material — contributes to this process.
If not properly maintained, soil can retain too much moisture, effectively suffocating (“drowning”) a plant’s root system. Alternatively, if the soil doesn’t contain enough moisture, the plant will be unable to absorb the nutrients it needs to survive.
The roots of a hydroponic plant have constant access to both air and water, and it can be much easier to maintain that balance since the roots are typically visible. The average plant needs at least five things to survive. (1) Air, (2) water, (3) nutrients, (4) minerals, and (5) light. So long as you can provide these things in plenty, your plants should stay healthy.
Growing your own food can be a rewarding experience. It’s a good way to save money on pesticide-free produce.
Although not necessary for the survival of a plant, substrate can help to support a plant physically and hold it upright, either by securing the root system, or by outweighing the plant itself. There are plenty to be found outdoors, especially near bodies of water. Even simple rock can alter the PH of your system. When checking your PH balance, be sure to check it after it has circulated through your substrate.
In the moisture-rich conditions hydroponics typically provide, substrate can be generally classified into the following categories: sandy, granular, and pebbled. If weight is not a concern, you might consider using a plant mulch, such as peat mulch or coir (coconut peat).
Mulches retain a high quantity of water, but also breathe very well. Mould and algae growth poses a higher risk when mulches are involved, but pose one considerable advantage over rocky substrate: they can be composted and replaced with fresh material. This is especially convenient if you use hydroponic systems exclusively to start seeds, or grow during the off-season. More at www.instructables.com/id/Understanding-Hydroponics/step1/Substrate-101/
Water alone is not enough to feed a plant.
In systems where the substrate is allowed to moisten and support roots, the substrate itself may be permeated with nutrients and minerals. In systems where there is no substrate, or the substrate is simply provided to support the plant physically, the water must be saturated with store-bought or homemade nutrient-and-mineral solutions.
The PH of your solution is important for the health of your flora, and the maintenance of your equipment. These solutions usually contain varying quantities of potassium nitrate, calcium nitrate, potassium phosphate, magnesium sulfate, iron, manganese, copper, zinc, and nickel. Potassium, especially, assists with healthy root growth. Salt is an important (but often forgotten) addition to the solution, as it tends to improve the taste of the plants grown.
Vermicomposting is a composting technique in which live worms are used to turn food waste into fertile soil. A handy by-product of the process is a nutrient-rich liquid commonly referred to as “worm tea”. Vermicompost can be suitable for indoor and outdoor composting.
In nature, plants photosynthesize white light from the sun. Sunlight is free. Use it where and when you can. There’s no reason you can’t build your system outside, after all, climate permitting. Alternatively, consider placing your hydroponic system in a room with plenty of natural lighting.
You can help mother nature along by using artificial light. Plants absorb red and blue light wavelengths efficiently, which stimulates growth. More importantly, plants absorb one more than the other. More at www.instructables.com/id/Understanding-Hydroponics/step3/Lighting-101/
In hydroponics, water can be delivered to a plant via local irrigation, or sub-irrigation. Local irrigation is a general term, describing the process of piping small amounts of water to individual plants. Typically this water is administered at the surface level. Drip and sprinkler irrigation works in this manner.
Sub-irrigation simply refers to any system which forces water to be absorbed from the bottom of a root system, to travel upwards — wicking techniques partially submersing the roots or substrate of a plant are common.
Water is a valuable commodity. If you can, be eco-friendly by collecting rain. Siphoning used aquarium water from your fishtank in lieu of a filter will provide a nitrate-rich nutrient solution for your plants and the moisture they need to survive.
source: instructables.com, photo from freedigitalphotos.net