In an ebb & flow system, why should GRODAN blocks be top irrigated (flushed) once a week?

The capillary movement of the blocks draws nutrients (salts) to the top in an ebb & flow system. If left unchecked, the salt levels in the top of the block can reach high levels, possibly damaging the roots.

This is why we recommend flushing the blocks once a week by top irrigating with standard nutrient solution. In fact, we recommend top feeding over ebb & flow systems for GRODAN stone wool. Refer to the brochure Watering and pH, Tips on watering and pH when using GRODAN stone wool for more information.