This is due to the wetting agent’s ability in lowering the surface tension of water which allows it to spread more easily and evenly in the peat. The wetting agent does not affect the total water uptake of the substrate so the plants, or more precisely the pots, do not take up any extra water because of the wetting agent added to the substrate.
There are two reasons for adding wetting agent:
Initial water uptake
When taking the packed peat – at packing moisture – into use, growers are adding water in order to maximise the expansion of the substrate. This is to gain maximum air capacity – providing good and well aeriated growing conditions for plants. The addition of a wetting agent secures the instant uptake of water making the substrate ready for direct use. The water addition causes the expansion and opening of the substrate and also increases the outturn volume of the packages.
Water uptake of plants
The wetting agent supports re-wettability of dried substrates during growing. The widely used practise of letting the substrate dry in order to compact the plants is basically only possible when there is a contained wetting agent which secures the re-wetting of the substrate. Plants in the corners of the greenhouse or tables are re-wetting better also due to the wetting agent.