Defining the Medium Culture in hydroponics
hydroponics, which is the growing of plants without soil by providing them with nutrients via water, can be accomplished in two main ways. Solutions culture hydroponics is a technique where roots are exposed to water on their own; the plants and the water are the only part of the hydroponic system. In medium culture hydroponics, the roots are encased in some sort of solid growth medium before they receive the nutrient water solution.
Medium culture hydroponics is somewhat controversial. Some argue its effectiveness makes it the superior hydroponic system of growing, above solutions culture. Others argue that the addition of a solid medium means that the growth process is not hydroponic at all. These nay-sayers complain that many of the growth mediums used actually supply some sort of nutrient to plants, making them, in effect, just like soil. Whatever objections some might have to using medium cultures in hydroponics, it is an extremely effective technique that is growing in popularity.
Medium cultures work in two ways; passive sub irrigation and top irrigation. Some mediums use one or the other, and some use a combination of the two. Substances that use passive sub irrigation generally have large spaces and gaps that allow oxygen to flow freely to the roots. A system of capillaries in the growth medium draws the water and nutrient solution inside and then circulates the nutrients to the roots. One variation of the passive sub irrigation method is called flow and drain, or ebb and flow, irrigation. In this technique, the plants and the growth medium are kept in a tray, and a pump sprays the growth medium with nutrient solution and oxygen at regular intervals. The growth medium then transports the nutrients and oxygen to the roots.
In the top irrigation method, the nutrient mixture is simply applied to the top of the growth medium. The medium then absorbs the nutrients and supplies them to the roots, which are buried deeper in the medium. Nutrients can be supplied using the top irrigation method as infrequently as once a day, for small plants, or as much as 5 to 10 times an hour, if using a pump to deliver the nutrients.
A wide variety of materials can be used as growth medium. Each medium has its benefits and drawbacks, and some are better suited to some plant types than others. Diahydro and expanded clay are two popular choices for growth medium, but they also come in line for a lot of criticism because their high silica levels supply the plants with additional nutrients. Rockwool is perhaps the most popular growth medium, but is should be handled with care. The particles in Rockwool can be dangerous to animals and humans if they are inhaled when they are dry.
Perlite, which is a type of volcanic rock, is becoming increasingly popular as a growth medium and may soon surpass Rockwool as the top choice. Perlite does a great job of maintaining healthy moisture levels in the roots while plants are growing. Vermiculite, another type of volcanic rock, also works well. Other common growth mediums include coco coir, which is the fiber from the husks of coconuts, sand, gravel, brick shavings, and even polyurethane packing “peanuts.”
Which growth medium you should choose depends on what plants are you are growing, and how large scale your operation is. Amateur growers may want to start out with inexpensive choices like sand or gravel, while larger scale farmers may find the reliability of perlite makes it the ideal choice for them. Despite the controversy, growth medium cultures are not likely to go away any time soon in hydroponics.