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How To Propagate Seedlings In Hydroponics

How To Propagate Seedlings In Hydroponics


Many thanks to the team at FloraMax for allowing us to use the content that makes up this guide! You can check out their article on seedling propagation here.

The Simple Way to Start Your Seeds

Methods for growing hydroponically tend to differ significantly from traditional outdoor gardening in many respects. The clearest example of this can be found at the earliest stages of cultivation - seed germination. 

In outdoor gardening, seeds can more reliably germinate when placed into the ground in their natural conditions. This is particularly true in many regions across Australia, with the exception of poor soil conditions and extreme climates... along with occasional wild weather events.

In a controlled indoor growing environment, however, seeds often require some help to get started. Without this assistance, your seeds are likely to remain dormant while swimming in an expensive nutrient solution.

Safe to say, growing indoors from seed without encouraging their germination is a surefire way to get nowhere fast. Even in the case of outdoor growing, planting without a germination process can be a risky move.

Thankfully, this outcome is by no means difficult to circumvent. Carefully nursing your seeds towards activation is guaranteed to maximise your chances of success.

Follow these steps carefully, and you'll be well on your way to sprouting fresh hydroponically-grown produce from seed.

Procedures for Propagating Seedlings

Propagating Seedlings in Australia

Before you really get started, first thing's first: you need to choose a medium for your seedlings to germinate in, and mature into.

Your choice of growing medium is essential. For the medium to be suitable, it ought to provide high oxygen and water levels and good drainage.

Rockwool is an extremely popular choice for seedling germination especially if Perlite, Vermiculite or Clay Balls are the final growing medium. Coco-coir plugs, such as the Eazy Plugs, are also very popular for seedling germination and have great transplanting synergy with Coco coir and organic living soil.

Secondly, you need to reduce the chance of disease.

Seeds should be sterilised prior to planting. Sterilisation of hardware and media before and during the propagation process is paramount.

Treatment Methods For Sterilisation

Soaking seeds in hot water (50 degrees C ± 1 degree C / 122 deg F ± 1.8 deg F) for ~25 minutes. With this method, note that seeds typically have a low tolerance to temperature error.

Soaking in 1% chlorine* solution for 5-10 minutes. Unlike the heat treatment method mentioned above, chlorine only sterilises the external surface of the seed.  *1 part household (50g/L) chlorine bleach + 4 parts water.

Steps for Germinating Seeds

Step 1. Thoroughly wash and sterilise all hardware. Be sure to sterilise any areas that are likely to come into contact with the seedlings, as this contact has the potential to cause disease.

Step 2. To increase the success rate of seedlings, use a heat mat and propagation lid.

The vents on the propagation lid need to be closed. Maintain root and air temperature at 20-25OC (68-77OF) and relative humidity at ~80%.

Note that cool conditions delay the germination of most seeds. This extends the length of time during which they are susceptible to fungal attack.

Step 3. Pre-soak the seedling's medium by immersing or drenching it with a pH buffered seedling nutrient solution. This will help remove any excess ‘alkalinity’ that is often present in the material. This step will also ensure that the medium is bedded down.

Allow excess nutrient to drain through. If you're using Rockwool, you can gently squeeze to remove any excess nutrient solution.

Step 4.

Option 1: Pre-germinating the seeds prior to planting them in the medium can be greatly beneficial, as it can help you identify the better quality seedlings.

Pre-germinate by placing the seeds between moist tissue paper on a plate. Cover this with an up-turned plate to keep the seeds in the dark. Check your seeds every few days, ensuring that the tissue does not become dry – sprinkle with water as necessary.

Once the “radical” (root) becomes exposed, place the seed in your medium of choice in an upright position, with the root pointing downwards. Locate the seed around 2 to 5mm (1/8 inch) below the surface.

Option 2: Sow the seeds at a depth equal to 2-3 times their diameter. Cover the seeds with your medium, and gently press down.

Step 5. Immediately after planting, lightly re-water using water or bloom nutrient solution at EC ~0.8mS (typically about one-third the normal strength). Continue to water the medium as required, typically every 2 or 3 days.

Maintain root and air temperature at 20-25OC (68-77OF) and relative humidity at ~80%. Diligently remove any dead leaves or seedlings – these are an ideal host for fungi.

Note: Some plant varieties or media may require little or no nutrient until the first few ‘true’ leaves appear (Fig 17.7b). If the success rate is poor, try feeding with plain water.

Step 6. Remove the propagation lid once the first shoot appears (Fig 17.7a). This will help prevent fungal diseases.

Step 7. Light is not required during the actual germination process. However, once the first shoot (‘plumule’) appears, the seedlings require light to begin photosynthesis. Light exposure prevents the plumule from becoming spindly or ‘etiolating’.

Use low intensity lighting for the first few weeks of growth. “Cool white” fluorescent lights are preferable. Position these ~10cm (4 inches) above the plants.

If your seedlings are being grown outdoors, position them in a partially shaded location. Too much light can stress seedlings in the early stages.

Step 8. Gradually expose the seedlings to their proposed environment. Depending on the plant variety, this may take only a few days, or many months. Begin to expose the seedlings to increased light intensity and nutrient strength. Ensure these changes are gradual, as a sudden change might kill them - after all, seeds are living organisms.

Step 9. Healthy seedlings can grow quickly. It is therefore essential to transplant them into a bigger system or container that provides adequate room for further root and shoot growth. Do this only after a minimum of 2 ‘true leaves’ have formed (Fig 17.7b).

Other Important Seed-Related Info

Collecting Your Seeds

As with cuttings, seeds should be collected from a plant that is healthy and has favourable characteristics such as a good yield and visual appeal. Seeds should be collected when mature.

Seeds that are immature will not germinate when planted. Immature seeds are soft and generally paler in color compared with mature seeds of the same plant species.

Seed Storage

To suppress germination while maintaining the integrity of the seed in a dormant state during storage, a cool, dark and dry environment is needed. A screw topped glass jar stored in a refrigerator is ideal.

Transplanting Cuttings & Seedlings

Plants are typically propagated (from seed or cutting) in a dedicated propagation system.

However, as they mature, this growing environment becomes unsatisfactory for future growth - there is insufficient room for root or foliar growth, a lack of light, etc.

It therefore becomes necessary to transplant them into a system that will support optimum growth through to the flowering / fruiting phase.

When transplanting, plant the entire root ‘block’ used in the propagation system. This will avoid disturbing the roots. If you have to remove the seedling from the propagation medium, ensure to be gentle with the roots:

  1. Allow the roots to settle naturally into the new medium. Do not allow the roots to become twisted or bent upwards (Fig 17.8).

  2. Plant the seedling to the same depth as it was before.

Now You Know!

If you're growing in harsh Australian outdoor conditions, or learning how to successfully nurture your seeds in an indoor hydroponic system, we hope this guide has come in handy.

For more resources relating to plant growth and hydroponics, be sure to check out our blog posts - and as always, you can find all of your hydroponic-related essentials on the Fran's Hydroponics online store!


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