Germinating seeds in hydroponics or aquaponics

Author: Aqua Gardening   Date Posted:9 December 2021 

For the best success with germinating seeds in hydroponics or aquaponics, our steps are a must read.

Before you start, you will need the following basic items:

  1. Grow media for the seed:
    1. A rockwool cube - grodan rockwool is what we use for water based hydroponic systems or aquaponics
      Grodan rockwool cube
    2. A jiffy pellet (peat moss) for a coco or soil system
    Jiffy pellets
  2. pH down and a pH test indicator to check your pH. pH down is an acid that is beneficial to plants.

For best results, you should invest in the following items (in order of importance):

  1. A propagator - tray and lid that helps to control the seed's environment
  2. A heat mat - a mat that has an adjustable thermostat or stays at an even 25°C
  3. Rooting tonic - specialised rooting solution to speed up growth and promote thicker roots. Comparing a rooting tonic to just using water is like chalk and cheese.
  4. CFL Propagation Lights - CFL grow lights are softer than sunlight. So you don't fry the sprout when it emerges, give it a controlled gentle light from a CFL lamp.

Germinating Seeds Steps

  1. Place your seeds in the freezer for 12 - 24 hours before planting out. This creates an artificial "winter" so when they are planted in a warmer place there is a clear signal to germinate.
  2. If you have some rooting tonic add 1-2ml of it to 1L of water. These products include Bloom RootsRhizotonic, or Roots Excelurator which speed up the plant?s growth after the seed opens.
  3. Without a rooting tonic, the balance the pH of your water down to 5.5.Tools for Propagation and Germinating Seeds
  4. Tools for propagating seeds and taking clones[/caption]
  5. Soak the rockwool cube or jiffy pellet  in the solution for a minute to make sure the water is dispersed throughout.
  6. Take the rockwool cube up out of the water and give it a very slight squeeze so it is damp but not water logged. The remaining solution can be used for watering later.
  7. Plant your seed at a depth of the width of the seed into the rockwool cube, so if the seed is 2mm width plant the seed 2mm below the surface. Make sure the seed is in contact with the rockwool.
  8. Place the rockwool on a lattice tray inside a propagation unit. Ensure the excess water can drain from the rockwool, and it is not sitting in solution.
  9. Use a heatmat under the propagator to keep the rockwool at 25°C (see instructions on heat mat label)
  10. Check the rockwool cube after a couple days. It should still be moist, if not spray or drop some of the root solution onto the cube. The rockwool should be kept moist but not water logged. With too much water there is not enough oxygen for the roots to grow and the seed and the roots will rot.
  11. When the seed has germinated and a leaf emerged give the sprout some light. PS1 Purple lights or other CFL grow lights for 18-24hrs a day are a good way of ensuring you don?t roast the seeds in direct sunlight.
  12. When roots emerge from the rockwool cube, add a solution of nutrient no higher than EC=1.0 to the tray. You can use 1/4 nutrient strength as a guide if you do not have an EC meter.
  13. Finally, when roots have emerged from the base of the cube or there is 2-3 nodes on the seedling, plant it out into your grow media.

The most common errors we see when germinating seeds 

  • Keeping rockwool cube too wet and causing the seed to rot ? use a lattice tray or a tray with plenty of drainage
  • Not providing warmth
  • Too much light before the seed has sprouted
  • Letting the air go stagnant (ie: not allowing fresh CO2-rich air into the propagation box.)

For more tips on growing and propagation with rockwool check out the book Gardening Indoors with Rockwool.