It’s spring and you just feel the need to start sowing. But how do you sow plants so that you can grow them hydroponically?

It is not so very different from classical sowing in soil. The basic principles remain the same, only the substrate is different.

What does a seed need to germinate?


Seeds are programmed to germinate at a certain temperature or after a cold period.


To germinate, seeds usually need to be rehydrated and then not dry once the germination process starts. Sometimes you’ll have to soak them in water and, in other cases, it the seeds will get the water from the surrounding air.


Seeds must have oxygen to germinate, otherwise they die and rot.


Some seeds need light to germinate, which information should be available in the sowing instructions.


The substrate must meet three conditions:

  • chemically inert: it may not contain harmful substances that may inhibit or prevent germination
  • water retention: the substrate must be able to absorb water so that there is sufficient moisture for the germination of the seeds
  • air permeability: after absorption of water there must still be enough air to circulate so the seeds get enough oxygen

The choice of the substrate will depend mainly on the size of the seeds: with too large substrate grains, the seeds fall through the substrate to the bottom of the pot.




Sand is especially suitable for very fine seeds. The disadvantage of sand is that it itself does not absorbs and retains water and, when the sand is too wet, the air circulation is very bad.

Sand is best for seeds that you can sow on the surface and form very small seedlings, such as cacti.

Moisten the sand but don’t let it be soaking wet or underwater.




Rock wool:

Rock wool has a good water retention/air circulation ratio and is suitable for very fine to medium seeds.

It is used in form of a mat or cubes with a hole for seeds or cuttings. Be careful with plants that form small seedlings, like cacti: if you sow the seed in the hole then the germ could be smothered at bottom of this hole.

The rock wool cubes are great: the roots grow through the cube and you can then plant the seedlings with block in another substrate. The risk of damage to the roots is minimal.

Place the rock wool cubes in a layer of water.





Perlite is particularly good for air permeability but not so good in terms of water absorption. It is suitable for sowing for hydroponics but keep in mind that it is very light in weight and it sticks to your fingers when wet. If you want to verify that you buried seeds germinate, it quickly become a mess. Perlite is suitable for medium-sized seeds.

Place the pots in a layer of water.





Vermiculite holds more water and is less air permeable than perlite. Keep damp but not wet so that there is enough air circulating. It is suitable for medium-sized seeds.

Place the pots in a layer of water.


Clay pellets:

Expanded clay pellets

Expanded clay pellets

Clay pellets are suitable for sowing large seeds, such as avocado, mango…

You can add water to the level of the seeds. Note that the seeds must be carefully stripped of all flesh so that no rotting occurs.

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