Propagation is simply the creation of new plants. Many growers propagate using hydroponic techniques to benefit from early rooting and faster growth rates. This is possible because hydroponic growing media provides the root zone with easy access to water, nutrient and oxygen.
Propagation: Seed vs. cuttings
Firstly, as with any type of propagation, you need to decide whether you want to grow from seeds or cuttings. Generally, growers who propagate from seed do so because it gives them peace of mind that their plants will be disease and pest free. However, the main draw back with seeds is that the characteristics of plants you produce can be inconsistent. Whereas, with cuttings you are producing plants that are identical to their healthy parent, this is why cuttings are also referred to as ‘clones’. Other advantages of cuttings include:
- Earlier flowering.
- Improved plant stock.
- Plant species which are more adaptable to climatic variations.
As growing from cuttings has so many benefits, at Aquaculture, we usually recommend our customers to use this method of propagation. However, for your first gardening venture you will probably have to start growing from seed. It is advisable to germinate several seeds at the same time. You will then be able to choose a mother (stock) plant from which you can take cuttings in future.
Setting up – You will need the following items:
- Propagation cubes/plugs.
- Rooting hormone.
- Heated or unheated propagator
- Fluorescent lighting.
- Sterile scalpel.
- Spray bottle.
- Rooting stimulator.
This article explains how to propagate using rockwool cubes. However, the process is basically the same for all types of propagation, such as Rapid Rooters and Jiffy-7’s.
The Mother Plant
You will have to grow your seedlings or cuttings under 18 hours of light until they are suitable to take cuttings from. This is usually when they are between 12-18 inches or have 8-10 internodes.
Label your seedlings with numbers or names so you can label your cuttings you take to correspond with the parent plant.
When your seedlings are ready, trigger them to flower by giving them 12 hours of light and 12 hours of darkness. Take the seedlings to full maturity to determine which shows favorable characteristics, i.e: quickest to root and/or best flower development.
While your plants are flowering, the cuttings will need to be kept in a vegetative state in a separate growing area with 18 hours of light and 6 hours of darkness.
The cutting with the same name/number as the plant with the most favorable characteristics should be kept as the mother plant.
Mother Plants can be grown in a variety of systems. We would recommend choosing a media based growing system as you will typically keep the plants for up to a year. Systems using techniques like NFT, bubblers (deep water culture) and aeroponics are more suited to short term crops.
The most popular method of keeping mother plants is using soil, or soil-less growing media in pots, which can be watered by hand or via and automatic delivery system.
Quality of cuttings
If you want strong healthy cuttings, it is important to consider the quality of the mother plant they are coming from. Make sure the mother plant is regularly trimmed to promote lots of side branches. This will give you more sites to take cuttings from. It is also advisable not to feed your mother plant too much. Overfed plants will produce thicker stemmed ‘woodier’ branches and cuttings that will take longer to root.
The highest concentration of growth is concentrated around the bottom 1/3rd of the plant around the inner shoots. This is where you should take your cuttings from. Growers often refer to this section of the plant as the ‘zone of juvenility’.
Without stripping more than 25% of the foliage, take as many cuttings from the mother plant as possible. Also, it is preferable to use cuttings which have a few leaves. Cuttings with large leaves tend to be unable to absorb sufficient water through their stem. Those with thinner stems will also root much faster than cuttings with fatter stems.
As stated above, seedlings/mothers need to be grown under 18 hours of fluorescent light and 6 hours dark. However, once they are well rooted, you will need to switch to 12 hours of HID light and 12 hours of dark to initiate flowering/fruiting.
In the first week, before the roots have formed, cuttings will perform best with the fluorescent lighting unit positioned 10 - 15 inches away from the propagator lid. When using HID lights for propagation you should only consider using 250w metal halide lamps. These should be positioned 3 feet away from your propagator. Higher wattage HID lamps will emit too much light and heat, and may result in your cuttings failing to root.
Rockwool propagation cubes
The main advantage of rockwool is that it holds more air and water than any other growing medium. Rockwool is also inert and sterile, and does not hold onto nutrient in any way. The roots are clearly visible and it is very easy to tell whether the cubes are moist or dry. They can be transplanted into larger rockwool blocks or any other hydroponic media with the minimum of fuss. Cuttings should take approximately 7-14 days to root. At this stage, you will need to transfer your cuttings into larger rockwool cubes or your chosen hydroponic growing medium.
A simple step by step guide to taking cuttings
- Clean all work surfaces and equipment with a disinfectant.
- Soak the rockwool cubes in a suitable nutrient solution for at least an hour. Shake the cubes to remove excess liquid. Plants need oxygen to root; rockwool which is too wet can prevent rooting and encourage disease.
- As highlighted above, you should take cuttings from the base of the plant, around the outer shoots. Choose shoots which have 3-4 sets of leaves. With a smooth motion, cut at a 45 degree angle just below the internode (branch/stem join).
- Immediately immerse the cut stems into a bowl of tepid water.
- Remove the bottom leaves from the stem. Also, if the cutting has more than one large fan leaf, remove the extra.
- With the scalpel, gently scrape the lower part of the stem. This will help initiate faster rooting.
- Apply the rooting hormone to the cut stem or cube, as directed on the product packaging.
- Gently insert the cutting into the cube. Lightly pinch the cube to hold the cutting in place.
- After all the cuttings are inserted into the cubes, place them back in their plastic tray and position in a propagator.
- Finely mist the cuttings with water, and then place the propagator lid on the tray.
- Place the fluorescent lights over the propagator.
- Give your cuttings 18 hours of light a day. However, if the air temperature drops by more than 4ºC when the light goes out, leave the lights on continuously.
- Once a day remove the propagator lid and finely mist the propagator lid.
- Roots should appear within 7-14 days. Once this is evident, the propagator vents can be opened.
- If you wish to transplant the propagation cubes into larger rockwool blocks, simply pre-soak the blocks with a suitable nutrient and a rooting stimulator.
- As with the cubes, it’s important that the rockwool blocks are not too wet. Insert the cubes into the larger blocks and place them onto a plastic tray or a surface on which the plants can be ‘air pruned’ (see below).
- Roots should appear on the bottom of the blocks within 2-7 days. After 10-14 days there should be loads of roots on the bottom of the blocks, at this point you can plant into your chosen hydroponic system. Do not be tempted to place your plants onto their system too early, only when there are an abundance of roots on the bottom of the blocks should you consider planting on.
This is a propagation technique used to help promote a healthy root system. It involves placing your plants in rockwool blocks on a perforated tray or wire mesh. This should be positioned so air can naturally flow underneath the blocks. With this technique as the root tip grows out of the blocks it detects the dry air and dies back. This forces the root, still within the block, to branch out forming more roots. This means the roots concentrate their growth within the block. Eventually you will have a plant with loads of small root tips protruding from the block with a large mass of roots within the block. Soon after the plant is put onto its final system the roots extend from the block very quickly, getting the plant off to a great start. This technique is particularly useful for NFT although should be employed for all types of systems.
Using Heated Propagators
If your propagation area is too cold your cuttings and seedlings will take a long time to establish. If you have temperatures below 18ºC inside your propagator you will need to use a heating mat or warming pad underneath your propagator, or buy a new heated propagator. When using heat from a mat, pad or heated propagator it is recommended you use about a 1/2 inch layer of perlite or vermiculite, or a mixture of both, in you propagator tray. This will help spread the heat throughout your propagator avoiding ‘hot spot’ areas.
Using ‘Aeroponic’ Propagators
Recent advances in propagation equipment has now made available affordable compact range of systems for propagating cuttings using aeroponics. With aeroponic propagation there is no need for any growing media, the main stem of the cutting is clamped in a sponge collar which is inserted into a net pot. This net pot is placed in the system where the stem gets a mist continuously sprayed around it. This promotes the ideal air to water ratio and cuttings often root within 5 days.
Once there are roots on the cutting you can transplant into a pot containing growing media. If you want to transplant into a large rockwool cube you can buy the large hole variations of the 3” and 4” blocks and fill in the space with perlite, vermiculite, coco coir or small clay pebbles. It is also possible to use small clay pebbles in the net pot, then place in your un-rooted cutting and place in the aeroponic propagator. The roots will still grow out quickly and the net pot can be placed straight into a Grodan 3” or 4” transplant block.
Q. My Cuttings won’t root
A. This is a very common question and can be due to a number of factors.
- The most common is the growing media you are using is being kept too wet. If you are using rockwool, after pre-soaking shake the cube to expel the excess water within the cube. When you spray your cuttings spray the foliage lightly not the cubes. Never leave water standing in the bottom of the propagator.
- Cuttings will take a long time to root if they are too big. Try to take smaller cuttings around 3” and remove the big leaves from the cuttings to reduce leaf surface area.
- Check your rooting hormone is still in date.
- Do not use strong nutrients to pre-soak cubes with, as this will inhibit root formation.
- Make sure the temperature is between 65-75ºF and is kept fairly constant. If your temperature falls more than 10ºF between day and night, keep your lights on continuously to maintain a constant temperature.
- Make sure you use a propagator and the vents are closed until roots appear.
- Be patient, the average time to root cuttings is 7-14 days.
Q. My cuttings are wilting
A. This can happen soon after taking the cuttings but they should come back around. If they stay wilted it’s usually a sign that temperatures are too high (common problem in summer months). Reduce temperatures in the propagation area.
Q. The base of the stem on seedlings/cuttings brown/black/rotting
A. This happens when the growing media is kept too wet which invites fungal diseases to attack the plant, collectively know as ‘damping off’ diseases. This is particularly problematic in warm and wet conditions.