Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

fertilizers, see Chapter Eleven, “Water and Nutrients.” Many of the same principles that apply to soil apply to the hydroponic medium.
     
----
    To remove roots and sterilize the growing medium:
    1. Manually remove the mat of roots that are entwined near the bottom of the bed, and shake loose any attached growing medium. It may be easier to add more medium than to pick it from between the matted roots
    2. Pour growing mediums such as expanded clay and gravel through a screen placed over a large bucket. Most of the roots will stay on the screen.
    3. Lay growing medium out on the floor, and train an oscillating fan on it to dry out remaining roots.
----
     
Nutrient Solutions
    To avoid nutrient problems, change the nutrient solution in the reservoir every week. Change nutrient solution every two weeks in systems with a large reservoir. Change the nutrient solution more often when plants are in the last stages of flowering, because they use more nutrients. You can wait to change the nutrient solution, but imbalances are more common. Plants absorb nutrients at different rates, and some of them run out before others, which can cause more complex problems. The best form of preventive maintenance is to change the solution often. Skimping on fertilizer can cause stunted growth. Nutrient imbalances also cause the pH to fluctuate, usually to drop. Nutrients used at different rates create an imbalanced formulation. Avert problems by using pure nutrients and thoroughly flushing the soilless medium with fresh tepid water between nutrient solutions.
    Hydroponics gives the means to supply the maximum amount of nutrients a plant needs, but it can also starve them to death or rapidly over-fertilize them. Remember, hydroponic systems are designed for high performance. If one thing malfunctions, say the electricity goes off, the pump breaks, the drain gets clogged with roots, or there is a rapid fluctuation in the pH, major problems could result in the garden. A mistake could kill or stunt plants so badly that they do not have time to recover before harvest.

Here is one of the many popular brands of liquid hydroponic fertilizer.
Solution Maintenance
    Plants use so much water that nutrient solutions need to be replenished regularly. Water is used at a much faster rate than nutrients. Casually “topping off” the reservoir with pH-balanced water will keep the solution relatively balanced for a week or two. Some growers top off the nutrient solution with 500-700 ppm-strength nutrient solution every two to three days. Never let the nutrient solution go for more than four weeks before draining it and adding fresh solution. Smart growers leach the entire system with weak nutrient solution for an hour or more between changing the reservoir. Wipe down the entire system with the solution.
    Do not flush with plain water. Flushing with mild (quarter-strength) nutrient solution will actually remove more excess fertilizer than plain water.
    Check EC of reservoir, growing medium, and runoff nutrient solution at the same time every day.
    Use an electronic EC pen to monitor the level of dissolved solids in the solution. Occasionally you will need to add more fertilizer concentrate to maintain the EC level in the reservoir during the “topping off” times. Keep the reservoir full at all times. The smaller the reservoir, the more rapid the depletion and the more critical it is to keep it full. Smaller reservoirs should be refilled daily.
     
----
    Nutrient Solution Composition
    The chart is a guideline of satisfactory nutrient limits expressed in ppm. Do not deviate too far from these ranges to avert nutrient deficiencies and excesses .

----
     
Hydro-Organic
    Hydro-Organic is a means of growing cannabis in an inert soilless medium and feeding with a soluble organic nutrient solution. Organic fertilizers are most often defined as containing substances with a carbon molecule or a natural unaltered substance such as ground-up rocks.
    Dedicated growers spend the time and trouble it takes to grow hydro-organically, because the natural nutrients bring out a sweet organic taste in buds. Indoor and outdoor crops grown in less than 90 days do not have time to wait for organic nutrients to be broken down. Organic nutrients must be soluble and readily available for short cannabis crops to benefit.
    An exact balance of organic nutrients can be achieved with constant experimentation and attention to details. Even when you buy ready-mixed commercial