The term propagation refers to starting of plants. There are two methods that are most widely used for plant propagation in hydroponics. These are seed germination and rooting cuttings (cloning).
Rockwool is the most popular propagating medium and is used as blocks or in loose or granular form. Rockwool blocks are 1″ cube in size with a hole ¼” deep at the centre. A flat of 98 such blocks fit into a standard tray. The rockwool blocks are soaked and pH balanced and one seed is placed in the hold. The seeds are then covered with a thin layer of Vermiculite or Perlite. The tray is then covered with a lid. When the seeds germinate the cubes are separated and placed into bigger growing cubes or other aggregate.
Though not used as extensively as blocks loose or granulated rockwool is also popular with hydroponics enthusiasts. Loose or granulated rockwool is taken in a standard plastic starting tray and the seeds are spread evenly on the medium. The seeds are then covered with a thin layer or rockwool or Perlite and the tray is then covered to prevent loss of moisture.
Cloning is a method of asexual propagation in which stem cuttings from a healthy plant are taken and then rooted. Most plants can be propagated using this method of asexual propagation. Cloning produces plants that are exact genetic duplicates of the original. These mature much faster which saves a lot of time. As oxygen is vital to the development of roots air pumps are often used to provide a steady supply of oxygen to the cuttings. Rockwool cubes, pH balanced with their flats soaked in a diluted, high phosphorus nutrient solution are widely used as propagation medium.
Using a clean, sharp blade, a small branch consisting of a growing tip with two or three leaves is cut. This clipping is then allowed to stand in water as the next clipping is cut. The procedure is repeated until the required number of clippings has been taken. A fresh cut is then made on each cutting just above the first cut. The clippings are then dipped in a rooting compound and inserted one inch deep into the rooting cube. The tray is then covered with a plastic dome to retain humidity and the plants are allowed to grow exposed to 18 hours of diffused light every day. As the plants will need fresh air for growth, the cover is removed for a few minutes every day. Mild foliar feed like kelp extract is used to mist the cuttings. The formation of roots can be checked by giving the plants a mild tug. Once the roots have formed the clones are transplanted.