alkalinity
Alkalinity is a measure of the bicarbonates and carbonates in the water. It is the primary factory causing the growing medium pH to rise. Fertilizer(s) and acids can be used to minimize pH fluctuations within the medium:
Low alkalinity water (0-100 ppm CaCO3) is typically deficient in calcium, magnesium and sulfate. Calcium containing, potentially basic fertilizers are often rotated with potentially acidic fertilizers mixed with Epsom salts. Cal-Mag fertilizers can be used, but media pH may slowly rise.
Moderate alkalinity water (101-225 ppm CaCO3) typically contains enough calcium. Epsom salts may still be required. Typically a potentially acidic fertilizer is used to control media pH.
High alkalinity water (226+ ppm CaCO3) contains sufficient calcium and magnesium. Acid injection is required, as media pH will rise. A potentially acidic fertilizer is used, depending on the alkalinity level in the acidified water.
Below are desirable alkalinity ranges for various container sizes. These ranges are only a guideline and the fertilizers recommended above should be used with these ranges. By adjusting fertilizer and / or acid inputs to accommodate the water alkalinity, the crops below will perform well in a broader alkalinity range.
 |
| Container |
desirable range
(CaCO3)
|
|
|
|
Plugs
|
60 -100
|
|
Small Pots (4” and smaller), Bedding Plant Flats
|
80 -140
|
|
Pots or Larger / Long Term Crops
|
120 -180
|
|
|
Water analysis
|
| element |
acceptable range
(in ppm unless otherwise stated)
|
high
(greater than)
|
|
|
| pH |
5.0 - 7.5a
|
|
| Soluble Salts (EC) |
0.2 to 1.0 mmhos/cm
|
1.3 mmhos/cm
|
| major elements |
a
|
a
|
 Nitrate (NO3)-N |
0 - 5
|
10bc
|
| Ammonium (NH4)-N |
0 - 5
|
10b
|
| Phosphorus (P) |
0 - 5
|
10b
|
| Potassium (K) |
0 - 5
|
10b
|
| Calcium (Ca) |
40 - 80
|
150
|
| Magnesium (Mg) |
20 - 40
|
75
|
| Sulfate (SO4) |
60 - 150
|
300
|
| minor elements |
a
|
a
|
| Iron (Fe) |
0 - 4.0
|
4.0
|
| Manganese (Mn) |
0 - 2.0
|
2.0
|
| Zinc (Zn) |
0 - 1.0
|
2.0
|
| Copper (Cu) |
0 - 0.2
|
0.2
|
| Boron (B) |
0 - 0.5
|
1.0
|
| Molybdenum (Mo) |
0 - 0.2
|
0.2
|
| other elements |
| Aluminum (Al) |
0 - 4.0
|
5.0
|
| Sodium (Na) |
0 - 50
|
80
|
| Chloride (Cl) |
0 - 70
|
80
|
| Fluoride (F) |
0 - 0.8
|
1.0
|
| Silicon (Si) |
Not Established
|
|
 |
| a |
Normal range for hydroponic culture. In a peat-based media, the pH of water is unimportant because, unlike alkalinity, it doesn’t influence media pH. |
| b |
These elements are typically low. If levels exceed 10 ppm it might indicate contamination from fertilizer or runoff. |
| c |
Maximum value as set by the EPA for drinking water. |
|
Low element levels: Low element levels can be corrected with addition of fertilizer.
Calcium: Supplement with a complete fertilizer containing calcium such as 13-2-13 , 14-0-14, 15-0-15, etc.
Magnesium: Use a complete fertilizer containing magnesium or supplement with Epsom salts d.
Sulfur: Use a complete fertilizer containing sulfur or supplement with Epsom salts d.
d One oz. Epsom salts per 100 gal. water provides approximately 7.5 ppm Magnesium and 32.6 ppm Sulfate. Do not mix with calcium fertilizers in the same stock tank. Small amounts can be added to phosphorus containing fertilizers. Consult your fertilizer manufacturer for recommendations.
High element levels: Depending on the level of element(s), constant leaching with a fertigation solution might correct the problem. In some cases reverse osmosis, deionization or other water treatment might be necessary.
