In hydroponics, as in any form of gardening, propagation is the term generally used to cover the planting and germinating of seeds and seedlings, the taking of cuttings, rooting and growing them on to a suitable size for transplanting.
Growing From Seed.
The growing of plants from seed can be a fairly precarious process, because the seed is susceptible to all kinds of attack. This can be due to moulds, bacteria, parasites or even predation by other living things. Seeds do not require any nutrition in order to start growing. In fact, nutrition at too early a stage can actually harm the growth of germinating seeds. All that is required for germination, the process of turning a dry, lifeless, seed into a growing, sprouting, life form, is moisture and warmth. Nature has provided all of the requirements for growth within the husk of the seed. Here they sit, dormant, until the environment is right for them to start their growth cycle.
There are many ways of germinating seeds. Some people drop the seeds into plain warm water for 24 hours, this is known as chitting, while yet others use a very dilute bleach solution in order to cut down on transmitted infections. Probably the most widely used method is to just place your seeds into pre-soaked rockwool starter cubes and sit the moistened cubes, in a shallow tray, in a warm, dark place. Spreader matting can be used instead of rockwool, moistened but not soaked. Yet another way is to use damp tissues or blotting paper, the methods are too numerous and varied to be listed here. The important thing to remember is that all that is needed is moisture and warmth. Cover the seeds with thin layer of substrate.
Within a short space of time, your seeds will split and start to produce root shoots. These will travel downwards towards the moisture. This process is closely followed by the emergence of the first cotyledon, or primary seed leaf. At this point the seed needs light as well as moisture and warmth. It is at this stage that you may start to consider nutrition. Because the plant still has the husk attached, nutrition is not yet vital to its survival, but a very weak solution of nutrients can give a boost to the production of sugars, which helps to kick start the plant growth.
As the seedlings roots grow and multiply and the shoot begins to grow upwards, the seed husk may well stick to the emergent cotyledon and rise above the ground level. At this point it is time to pick out the weak and non-germinating seeds. These should be discarded. If you are using a propagation system that has a thin membrane like blotting paper or tissue, you should now transfer your seedlings, complete with their own individual piece of membrane, to a propagation tray , or pre-soaked rockwool cubes etc. Ensure that the tray has an opaque cover to allow the light in.
The aim with hydroponics based propagation is to produce a good, strong, root system that will be able to absorb as much nutrient as the plant requires. This necessitates ensuring that the roots are in darkness, so cover the system if needed, leaving holes for your top growth. Within a fairly short space of time, the seedlings should grow into healthy, vigorous, young plants, ready for transplanting into their maturing beds.
It is now that your final choice of system comes into play. If you have chosen some form of ebb and flow system, or another rockwool based setup then you only have to put your propagation, or starter, cubes into larger ones. If you are going for an inert medium like Perlite or clay pebbles then you must carefully tease the delicate roots from the rockwool. This is best done by carefully tearing the rockwool cube apart and then extricating the root ball. If, of course, you have used a potting mix of Coir and or some other substrate, then your task will be a lot simpler.
One word of caution, however, don’t use one of the sterile, inert, high drainage products, like expanded clay pebbles, as a propagation starter medium for your seedlings. These substrates do not hold the water well enough and you run the risk of your new, tender, roots drying out. They can of course be used if mixed with a conventional substrate.
Propagation From Cuttings, Or Cloning.
Photo: Growth Technology Ltd
Taking cuttings from a mother plant and rooting them is by far the most popular way of starting out for the hobby hydroponics gardener. The technique involves taking cuttings from the vigorous, healthy, shoots of a mature plant. All of these cuttings will become clones of the mother plant. This means that each plant will have the same DNA as the mother plant and will grow to look the same.
Small cuttings, about one inch long, with two to three small leaves left and all the others removed are very energy efficient. These small clones have the advantages of using less of their limited reserve of energy than larger cuttings and they will not wilt as quickly. This means that they will remain green and productive, as their roots start to develop.
The cutting should be done just below the point where a leaf attaches to the stem (a node), using a clean, sharp knife. Strip the leaves from the lower half of the clone; apply a very small amount of rooting hormone to the freshly cut end and plant into a prepared, pre-soaked, rockwool, propagation cube. Cleanliness is vitally important at this stage. Use new or freshly cleaned containers to avoid diseases. Do not allow your cutting to come in contact with any dirty surface and do not cross contaminate your rooting hormone.
If you do not have access to a propagation tray, you can plant several clones into a 6” to 8” plastic pot. Place the pot in a plastic bag to keep the humidity levels up. Don’t forget to open the bag each day to allow for air changes. The clones should be kept moist, but not wet, until sufficient root system has grown and they can be transplanted or the pots put into a suitable hydroponic system. This process normally takes approximately 10 to 14 days.