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The Challenges of Growing in Hard Water

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Many growers are faced with the challenge of growing crops in hard water. If you have grown in hard water you’ll know how difficult it can be. The pH is difficult to maintain, the starting E.C. is high and calcium deposits block drippers and the nutrient profile quickly gets out of balance. By hard water, we are talking about water with more than 60ppm calcium. If you are in any doubt, ask your local retailer to arrange a water analysis.

The reasons that these are a problem? Firstly, the blocking of drippers is obvious so we don’t need elaborate on that.

Secondly, the pH is difficult to maintain. Because the water contains bicarbonates, you are adding pH up every time you add water. Then, as a rule, you will add pH down to counteract the problem. This can cause calcium phosphate to precipitate out. In addition, the bicarbonates in the water react with carbon dioxide in the air and in the water and create calcium carbonate (limestone) which deposits in dripper lines and in the medium. And that’s only the pH problems.

The third major problem is the high starting E.C. If your feed schedule calls for nutrient and additives to reach a target E.C of, say, 2.0, a grower with soft water (low salt) will be able to put in all that is required. With hard water, however, there is not enough “room” to put in everything your feed programme calls for. For example, if your water has a starting E.C of 0.5, that means you can only add nutrients/additives to 1.5E.C in order to reach your target E.C of 2.0. You may therefore be depriving your plants of vital nutrients or additives.

There are several actions a grower can take.

  • The best action is to set up your operation in a high quality soft water area. This, however, is understandably impractical for most growers.
  • By far the next best way to tackle this problem is to install a Reverse Osmosis (RO) machine. Instead of trying to manage the hard water – eliminate it. RO machines are not expensive these days, and your plants will love you for it. We typically see the investment in an RO machine repaid many times over IN THE FIRST CROP.
  • If you can’t, or don’t want to install RO, then medium and irrigation management is your only other option. For recirculating systems, have at least 15 litres of reservoir capacity per plant and dump the solution every three days. For run-to-waste systems, you will need a free draining medium and irrigate 50% more often. Also make sure that the runoff is at least 50% of what you irrigate. By taking this approach, even though your nutrient solution will contain less nutrient/additives than is desirable, you will be putting more fresh solution past the roots and ensuring that your plants have access to the full nutrient profile, all the time. Also, keep in mind that smaller, younger plants will need less management than larger, older plants.

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