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DIY Hydroponics - Hydroponic Media


The growing medium serves the vital role of providing support to the root system of the plant and allow the roots access to the oxygen, water and nutrients that are important for the wellbeing of your chosen crop.

There are numerous different type of hydroponic media and selecting the media appropriate to the method of hydroponics that you use can pay dividends in crop yield and the growing performance of your plants. The hydroponic media that you select will completely replace the use of soil and must allow the plant roots access to oxygen and nutrient solution in appropriate amounts. Wick feed systems will work better with perlite and vermiculite mixed at a ratio somewhere between 5:1 and 10:1 (more perlite, the white one) as this mixture will allow water to climb up from the reservoir through the medium more effectively than hydroclay. A top feed system on the other hand works well if the plant is grown in a rockwool cube placed on top of a bed of hydroclay where the nutrient will drain more freely when the pump is not running and encourage aeration. This combination works acceptably for flood and drain systems too.

As a general guide consider the way your root system will have nutrient delivered to it. Active hydroponics systems such as top feed or flood and drain systems will have nutrient delivered to it automatically because smart growers will put their pump on a timer. The timer will run for a specific duration a set number of times during the day saturating the roots and the interval between pumping times can be fine tuned so that the plants have time for the nutrient solution to drain and the roots to receive oxygen. Passive hydroponics on the other hand relies on the growing medium being moistened by capillary action, that is the nutrient solution will dampen the media that it is exposed to and will climb from the reservoir to surround the root system. Media used in this method should be able to retain moisture and air at the same time. Although all hydroponic media has this property the proportion of air and nutrient varies between the different types.

When evaluating a soilless medium for use consider its texture and partical size. Fibrous materials such as perlite/vermiculite, peat or some coconut products hold a great deal of moisture in their cells and have smaller particles making them ideal for wick systems. Irregularly shaped materials have more surface area and can hold more water but avoid anything with very sharp edges as this can cut your plants roots. Larger particles such as pea gravel, crushed brick or hydroclay drain faster and hold more air making them ideal for active hydroponic systems.

Rockwool should definetely not be overlooked and for raising seedlings or cuttings it is invaluable. It is inert, sterile, porous and provides good firm support for root systems. Even when completely saturated rockwool can still hold up to 20% air. Its major drawback is that it has a PH of 7.8-8 and buffering may be required to bring the PH down to 6.5. Rockwool is usually purchased in cubes about 10cm high wide and long or in slabs of varius sizes, most commonly 20cm X 20 CM X 100cm. I have had good results using rockwool in my top feed system. I generally raise my cuttings in a seedling sized cube about 3cm X 3cm X 5cm. When they have started to grow and the roots are starting to protrude through the side of the cube I transfer them from the cutting tray into a 250mm standard plastic pot. The pots bottom should be filled with hydroclay at least 5cm deep, then the next layer is simply cut from a rockwool slab and is about 15cm deep. The young plant is placed in a 10cm rockwool cube on top of the rockwool slab and then hydroclay is added around the sides of that cube to hold it in place.

Regardless of your choice of hydroponic medium it should be sterilized as best can be done before it is used. In the very least place it under running water to remove any dust or particles resulting from the medias manufacture. Rock wool should be soaked in water for an hour and rinsed thoroughly before use. During the course of the growing season salts and other undesirables will build up in the medium making it toxic to your plants. With active systems every two weeks or so the nutrient should be replaced with water and the pump run for 24 hours straight to loosen up, dilute and remove built up undesirable material. Wick systems can be taken outside and flushed for half an hour with a hose or, if this is impractical, fed with straight water for a few days.