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Submitted by: Larry

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'How often should I water an ebb and flow system with grodan grow cubes' is an excellant question! Grodan grow cubes are basically compressed blocks of stonewool otherwise marketed as 'rockwool'. And these blocks have excellant water retention properties. Since we know that an ebb and flow hydroponics system will flood plant roots with nutrient solution at timed intervals what should the timed intervals be when using grodan substrate? Theoretically an ebb and flow system floods for 10 or 15 minutes then drains allowing the growing medium or substrate to dry before the next flood. If not allowed to dry, the substrate may encourage root rot, damping off or any of a number of fungal and bacterial infections. Since grodan retains water so well, the timed intervals should be lengthened for ex: an ebb/flow system flooding once an hour with a loose substrate such as clay balls would probably only need to be flooded once every 3 hours when using grodan. And this all depends on relative humidity and other factors that affect the rate of water evaporation. Sound complicated? It's really not. All you need to do is flood the plants, pick a flood interval and just before the plants flood again (say 3 hours) check the grodan cubes. If they are almost dry then it is time to water, if not then extend the interval. Always check your plants and their growing medium and let them 'tell' you what they need and you cannot go wrong.

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