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The Hydroponics Manual: Propagation For Hydroponics

Propagation is about starting new plants for your garden, for indoors or to give to friends. Plants can be started from seed or cuttings...

There are many different techniques of propagation for different species. We can only give general guidelines which will be suitable for a wide range of plants. If you plan to propagate difficult or unusual species, we suggest you refer to any of the fine books on propagation available at your local library.

The approach to propagation outlined here is based on the latest current commercial practices. It is intended as an introduction to the most up to date professional techniques such as the use of rock wool and hormone rooting gels.

Rockwool propagation cubes are ideal for starting larger plants such as tomatoes, for instance, because they allow the grower to sort through the young plants and select the best for planting on. Rockwool takes a little getting used to but we recommend that you persevere because once you have mastered the technique, you will have a very useful skill and an unlimited supply of new plants whenever you want them...

There are several types of rockwool designed for propagation of seeds and cuttings. Best for the home grower is the single block system, known as SBS.

Rockwool SBS consists of small individual cubes or mini blocks of rockwool in a plastic tray, contained within its own compartment. Each mini block is thus separated from the others so the roots of the new plant cannot invade the neighbouring blocks. These SBS have now become known as "cubes". SBS is widely used by commercial growers the world over and is now at last available to the enthusiastic amateur. The features that attract the professional will delight the hobby gardener. A uniform product ensures uniform results. Once you have the hang of using rockwool, you will get consistent, predictable results and an endless supply of new plants from seed or cuttings. You will find the new plants very easy to handle regardless of the numbers and they can be planted on in a number of ways as you will see below. They also make ideal plants to be sold or given away.


Electric heated propagator. Advantages Disadvantages




A: Starting From Seed

  1. Soak rockwool SBS tray in lukewarm water or a weak and slightly acidic nutrient solution. Formulex is highly recommended as a conditioning solution for rockwool as it will stablise the pH and supply a full profile of mineral nutrition to the young plant. Allow plenty of time for rockwool cubes to take up water. Stand it to drain.
  2. Insert seeds carefully into the holes marked out on top of the cubes. Donít push them in too far, just enough to hide seeds. A few strands of rockwool should be teased over the hole to ensure that seeds are covered.
  3. Place rockwool SBS tray in a warm place. Light is unimportant until the seedlings begin to emerge but must be supplied as soon as they do. Ideal germination temperatures for most species are in the range 20-25°C. These temperatures should be maintained as constantly as possible during the germination period. Check the moisture level of the rockwool every day. If you just squeeze a corner of a cube, water should come to the surface. If it does not then you should give the whole tray a light sprinkle of lukewarm water.
  4. The biggest mistake with rockwool is to keep it too wet and this usually occurs through poor drainage. Never let your rockwool stand in a puddle of water, always allow free drainage underneath the tray.
  5. Once your seedlings begin to appear you will need to give them plenty of light, a warm sunny windowsill might do but a greenhouse or artificial lights will be best. Fluorescents are very suitable for small seedlings or cuttings. It is still important to maintain temperatures in the mid twenties for as much of the day as possible. Keep checking your rockwool cubes for signs of drying out.
  6. Once your seedlings begin to show roots at the bottom of the rockwool cubes it is time to think about planting them out.
  7. Just lift the little cubes carefully from the tray. Your new seedlings are now ready to plant into soil in the normal way OR to be cultivated further in rockwool or other hydroponic systems.

B: Starting From Cuttings

If you already have access to healthy plants that display desirable characteristics, it is possible to clone new plants from them. These new plants will be genetically identical to the parent plant and provided that the environmental conditions are constant, the new plants should perform exactly as their parent did.

  1. Soak rockwool SBS tray in a weak acidic nutrient solution (pH 5/1.5 mS). Formulex is ideal for this. While the rockwool is soaking you can be selecting material for cuttings. Most species are propagated best from softwood tips. Selected material should show signs of healthy vigorous growth. Stems should be thick and firm and foliage should be dark green.
  2. Remove selected piece from mother plant with sharp scissors, taking care to cut plant at least 10mm below the point where the final cut will be made. Final cut should be made with a sterile scalpel or clean sharp razor blade just below a node or leaf junction. A diagonal cut is preferred as it allows more plant tissue to come into contact with the rooting compound.
  3. A highly recommended rooting gel is Clonex. Pour a small amount into a small container. Immediately dip the cut tissue into the Clonex, ensuring that all cut surfaces are well covered. Wipe off surplus against the side of the small container. Do not return any of the unused Clonex back to the original container as this might contaminate the remaining gel.
  4. Insert cutting into hole in top of rockwool cube. It is very important not to push it in too far, just enough to support it in an upright position.

Clonex Hormone Rooting Gel

Clonex is a high performance rooting compound in a gel form. It is a tenacious gel which will remain in contact around the stem, sealing the cut tissue and supplying the hormones needed to promote root cell development and vitamins to protect the delicate new root tissue. Clonex has a full spectrum of mineral nutrients and trace elements to nourish the young roots plus anti-microbial agents to protect against fungal contamination. It achieves a better success rate and much faster root growth than hormone powder or liquids.

Ideal Conditions for Rooting


For most species, the ideal rooting temperature is around 23-28°C. Heat is best supplied from underneath (bottom heat) to warm the rockwool and encourage root cell initiation. It is most important that temperature remains constant.


Humidity is of critical importance because the little plants have no roots to begin with. Maintenance of high humidity around the leaves will protect them from wilting until new roots appear.


Unlike the seeds that we planted, your cuttings will need light from day one. Filtered sunlight will be okay but the best results will be achieved with fluorescents or low wattage high pressure sodium. Light should be supplied to cuttings for at least 16 hours a day.

Once all cuttings are in place, mist them thoroughly with tepid water and place in suitable location. We highly recommend a propagation tray which is large enough to hold an SBS tray and which has very high sides to accommodate large cuttings as well as vents to control the humidity level.

To encourage speedy root initiation on your cuttings, it is necessary to pay attention to the environment in which this is taking place...

Provided that you have maintained the right conditions, your cuttings should start rooting very quickly although the time will vary from species to species. Roots will start to appear at the bottom of the rockwool and as soon as they do, it is time to plant out. You will probably notice that the little cutting has a much more vigorous root system than the seedlings. This is one of the ways in which cuttings are usually superior to seedlings.

You will now have a number of seedlings or cuttings in your SBS tray. This is the time to select the best for growing on. Never try to separate the little plant from its cube. It is intended that cubes will stay with the plant throughout its life. You will find these little cubes extremely easy to handle, in fact, that is why the professionals use them. Once you have selected the best plants you can grow them on in rockwool in several different ways.

The above instructions are a general outline of the procedures involved in starting new plants from seeds or cuttings. There are many species of plant that need specialised techniques for propagation. African violets for instance are propagated from leaf cuttings. It is not possible to cover all species and requirements in this fact sheet. If you wish to propagate difficult species, it is strongly recommended that you consult a specialised book on propagation. If you want to experiment, follow these basic instructions and make any necessary modifications as you go.

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