media pH
Low pH: For upward pH adjustment (less than 0.5 pH unit), use a complete fertilizer with potential basicity until pH is corrected. For greater pH adjustment use potassium bicarbonate, flowable limestone or powdered limestone.
High pH: To reduce pH, use a complete fertilizer with a high potential acidity. Injection of acid (i.e. sulfuric, phosphoric, nitric) might be necessary in extreme cases.
media E.C. (electrical conductivity)
Low E.C.: Increase fertilizer rate or frequency of application. Check both the fertilizer concentration in the stock tank and the injectors*.
High E.C.: Leach media with weak fertilizer solution. If fertilizer salts are very high in the media, leach with clear water. Check both the fertilizer concentration in stock tank and the injectors*. Always water thoroughly to run through to minimize soluble salt accumulation.
* Fertilizer injectors can be calibrated by measuring the electrical conductivity (E.C.) of the fertigation solution with an electrical conductivity meter.
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pH*
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EC
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Soilless Mixes
(<10% Soil)
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Soil-Based
Mixes
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Rating
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(mmhos/cm)
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5.00-5.49
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5.50-5.99
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Low
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<0.75
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Low
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5.50-6.49
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6.00-6.99
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Normal
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a |
0.76 - 2.49**
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Normal
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6.50-7.00
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7.00-7.50
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High
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2.50 - 3.50***
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Normal to high
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| * |
The pH ranges apply to in-use growing medium. Ratings (low, normal, high) apply for most crops but there are exceptions. Dry, unused soilless growing media might have a pH lower than 5.5 because the limestone did not dissolve; to check the pH of unused growing media, thoroughly wet a sample and measure the pH after 3 days). |
| ** |
Normal range for most plants; E.C. range for most plugs should not exceed 2.0 mmhos/cm. |
| *** |
Normal range for heavy feeders or crops irrigated with high E.C. water. |
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media nutrients
Low nutrient levels: When one or more nutrients are deficient in the growing media, it is best to apply a complete peat-lite fertilizer. This will minimize nutrient imbalances and pH fluctuations.
Excessive nutrient levels: If one or more nutrients are excessive, but soluble salts are normal, leach with a complete peat-lite fertilizer at a moderate recommended rate for that crop. If soluble salts are excessive, leach with clear water.
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| nutrient |
if deficient
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if excessive
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Calciumab
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Use complete fertilizers containing calcium:
13-2-13, 14-0-14, 15-0-15, 15-5-15, etc.
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Avoid calcium fertilizers and reduce pH to lower end of normal range.
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| Magnesiumab |
Use complete fertilizers containing magnesium: 13-2-13, 14-0-14, 15-5-15, etc. OR epsom salts (magnesium sulfate).
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Avoid magnesium fertilizers and reduce pH to lower end of normal range.
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| Sulfateab |
Use complete fertilizers containing sulfate
OR epsom salts (magnesium sulfate).
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Avoid sulfur fertilizers and if used, check sulfuric
acid rates.
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| Iron, Manganese, Zinc, Copper, Boron and Molybdenumb |
Use a peat-lite fertilizer or supplement with a micronutrient fertilizer (e.g., S.T.E.M.).
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Check irrigation water for excessive nutrient levels. Leach with a complete fertilizer.
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| Sodium, Chlorideb |
n/a
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Leach with a complete fertilizer.
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| a |
Test your water to determine the level of calcium, magnesium and sulfate. Some water sources might not have sufficient quantities of one or more of these elements.
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| b |
Your water might contain excessive levels of the particular nutrient. |
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pH is determined in non-filtered saturated media. Nutrients and E.C. (electrical conductivity) are determined by saturated media extract (SME)
Media solution extraction accounts for differences in water holding characteristics of different media.
Media analysis indicates the fertility status only at the time of sampling. Performing tissue and media analyses at the same time will provide more complete information about the status of a crop. Sampling both healthy and unhealthy plants might provide a comparison useful for diagnosis.
