Water testing is one of the industry’s most underutilized tools for managing crop nutrition. Services offered by a horticultural water testing lab will include measuring pH, alkalinity, and EC (electrical conductivity or soluble salts) as well as levels of macro and micronutrients that are relevant to plant production. Understanding the impact of these key analytes allows growers to create precise nutrition plans and avoid undue damage to sensitive crops – let’s start from the beginning.
Irrigation water generally comes from three sources. Pond water, which may also be a catch pond to reclaim irrigation water, can vary drastically in nutrient content due to its exposure to fertilizer runoff, rain events, and evaporation over time. Well water is perhaps the most common source of irrigation water and can vary greatly between different regions or even locally. Municipal water, or “city water,” is treated to preserve the infrastructure of the pipes that distribute it. This treatment results in less seasonal variation in water quality, although utilizing this source incurs an additional cost for the grower.
A pH reading is a measurement of the acidity or basicity of a solution. In general, water for irrigation should have a pH between 5.0 and 7.0. Water with pH below 7.0 is acidic and water with pH above 7.0 is basic. Water with a pH 7.0 is neutral. Knowing the pH of the water is important because it generally gives us an idea of what else might be in your water. For hydroponic producers, solution pH equates to root zone pH, however, solution pH has very little impact on substrate pH in field or container production. When growing in peat or pine bark-based medias, alkalinity is the primary driver for soil pH change.
Alkalinity is a measure of the dissolved bicarbonates (i.e., calcium, magnesium, and sodium-based) in water. These bicarbonates all create a basic reaction in the substrate and predict what your water will do to media pH over time. The higher the alkalinity, the greater the upward pressure on media pH. If excess alkalinity is not accounted for it causes a gradual “liming of the media”. Very low alkalinity water does not buffer or resist the pH change that many fertilizers create. This can lead to plummeting media pH if heavy acid forming fertilizers are used extensively (e.g., 20-10-20).
Electrical conductivity (EC) is a measure of dissolved salts. The EC of water applied to the crop must be known to balance adequate nutrition while avoiding high soluble salts levels in the media. The goal is to provide adequate nutrition to the crop while avoiding excessive fertilizer applications and accumulation of salts in the substrate. A water source with high starting EC levels presents problems, because this water can limit the amount of fertilizer that can be applied. Knowing the starting water EC allows us to correctly calculate the fertilizer rate used to feed the crop.
Once we understand these key measures of water quality, we can craft a fertilization plan that optimizes our plant nutrition strategy while reducing potential problems. The GGSPro general fertilizer programs correlate to broad alkalinity ranges and are further optimized for crops preferring low or high media pH. Media pH can generally be managed through fertilizer selection when water alkalinity is less than 150 ppm CaCO3. For water with alkalinity greater than 150 ppm CaCO3, acid injection is recommended. The GGSPro general fertilizer programs rely on a rotational approach to balance media pH while providing an adequate assortment of nutrients to encourage optimum growth. Each program will call for a rotation between an acid forming fertilizer (Type A) and a calcium-based formulation which provides a basic reaction (Type B). See Table 1.
Table 1: Common Rotational Fertilizer Choices
Griffin Greenhouse Supply represents many partners that manufacture water-soluble fertilizers. Exact selection of Type A and Type B fertilizers is determined by grower preference/needs. Often times, Epsom salts (magnesium sulfate) may be added to formulations in the Type A group but should not be added to calcium containing fertilizers (Type B group) when using concentrated stock tanks. Two subcategories of each fertilizer program address optimal crop pH needs. Crops not listed are less sensitive to media pH and are often grown under either pH strategy. See Table 2. Please note, your specific production scheme may not allow for fertilizer rotation to feasibly be maintained – there are many strategies available to help manage pH and overall plant nutrition. Work with GGSPro to find the right approach for your situation.
Table 2: Spring Crop pH Preferences
Despite using pH adjusted growing media and best practices, there are times when soil pH falls below or rises too high for optimum crop production. Irrigation water quality, fertilizer selection, and even the crop itself can cause significant changes to the pH. Substrate pH affects the availability of micronutrients to the crops we produce. At high pH, the majority of our micronutrients (e.g., iron, manganese, zinc, and boron) become less available. Conversely, at low pH, these can become excessively available. Griffin Greenhouse Supply offers a variety of products that help manage substrate pH or the symptoms caused by suboptimal substrate pH as shown in Table 3. Please reach out to GGSPro or your local Griffin sales representative for more information and labs that provide appropriate water testing services. GGSPro can also talk through water test results and help formulate a fertilizer program to meet your specific crop needs.
Table 3: Products for Managing pH Problems
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!
Irrigation water generally comes from three sources. Pond water, which may also be a catch pond to reclaim irrigation water, can vary drastically in nutrient content due to its exposure to fertilizer runoff, rain events, and evaporation over time. Well water is perhaps the most common source of irrigation water and can vary greatly between different regions or even locally. Municipal water, or “city water,” is treated to preserve the infrastructure of the pipes that distribute it. This treatment results in less seasonal variation in water quality, although utilizing this source incurs an additional cost for the grower.
A pH reading is a measurement of the acidity or basicity of a solution. In general, water for irrigation should have a pH between 5.0 and 7.0. Water with pH below 7.0 is acidic and water with pH above 7.0 is basic. Water with a pH 7.0 is neutral. Knowing the pH of the water is important because it generally gives us an idea of what else might be in your water. For hydroponic producers, solution pH equates to root zone pH, however, solution pH has very little impact on substrate pH in field or container production. When growing in peat or pine bark-based medias, alkalinity is the primary driver for soil pH change.
Alkalinity is a measure of the dissolved bicarbonates (i.e., calcium, magnesium, and sodium-based) in water. These bicarbonates all create a basic reaction in the substrate and predict what your water will do to media pH over time. The higher the alkalinity, the greater the upward pressure on media pH. If excess alkalinity is not accounted for it causes a gradual “liming of the media”. Very low alkalinity water does not buffer or resist the pH change that many fertilizers create. This can lead to plummeting media pH if heavy acid forming fertilizers are used extensively (e.g., 20-10-20).
Electrical conductivity (EC) is a measure of dissolved salts. The EC of water applied to the crop must be known to balance adequate nutrition while avoiding high soluble salts levels in the media. The goal is to provide adequate nutrition to the crop while avoiding excessive fertilizer applications and accumulation of salts in the substrate. A water source with high starting EC levels presents problems, because this water can limit the amount of fertilizer that can be applied. Knowing the starting water EC allows us to correctly calculate the fertilizer rate used to feed the crop.
Once we understand these key measures of water quality, we can craft a fertilization plan that optimizes our plant nutrition strategy while reducing potential problems. The GGSPro general fertilizer programs correlate to broad alkalinity ranges and are further optimized for crops preferring low or high media pH. Media pH can generally be managed through fertilizer selection when water alkalinity is less than 150 ppm CaCO3. For water with alkalinity greater than 150 ppm CaCO3, acid injection is recommended. The GGSPro general fertilizer programs rely on a rotational approach to balance media pH while providing an adequate assortment of nutrients to encourage optimum growth. Each program will call for a rotation between an acid forming fertilizer (Type A) and a calcium-based formulation which provides a basic reaction (Type B). See Table 1.
| Type A | Type B |
|---|---|
| All Purpose Fertilizers (acid reaction) |
Calcium Based Fertilizers (basic reaction) |
| 21-5-20 | 15-0-15 |
| 20-10-20 | 15-0-14 |
| 20-3-19 | 13-2-13 |
| 19-2-19 | 15-5-15 |
Griffin Greenhouse Supply represents many partners that manufacture water-soluble fertilizers. Exact selection of Type A and Type B fertilizers is determined by grower preference/needs. Often times, Epsom salts (magnesium sulfate) may be added to formulations in the Type A group but should not be added to calcium containing fertilizers (Type B group) when using concentrated stock tanks. Two subcategories of each fertilizer program address optimal crop pH needs. Crops not listed are less sensitive to media pH and are often grown under either pH strategy. See Table 2. Please note, your specific production scheme may not allow for fertilizer rotation to feasibly be maintained – there are many strategies available to help manage pH and overall plant nutrition. Work with GGSPro to find the right approach for your situation.
| Low pH | High pH |
|---|---|
| pH = 5.3 to 5.8 | pH = 6.0 to 6.5 |
| Ivy geraniums, petunias, calibrachoa, pansy, vinca | Seed and zonal geraniums, N.G. impatiens, African marigolds, lisianthus, pentas, lilies |
Despite using pH adjusted growing media and best practices, there are times when soil pH falls below or rises too high for optimum crop production. Irrigation water quality, fertilizer selection, and even the crop itself can cause significant changes to the pH. Substrate pH affects the availability of micronutrients to the crops we produce. At high pH, the majority of our micronutrients (e.g., iron, manganese, zinc, and boron) become less available. Conversely, at low pH, these can become excessively available. Griffin Greenhouse Supply offers a variety of products that help manage substrate pH or the symptoms caused by suboptimal substrate pH as shown in Table 3. Please reach out to GGSPro or your local Griffin sales representative for more information and labs that provide appropriate water testing services. GGSPro can also talk through water test results and help formulate a fertilizer program to meet your specific crop needs.
| Raising pH | Lowering pH | Nutritional Deficiencies |
|---|---|---|
| CalOx pH | Sulfuric Acid 93% | Calcium Chloride DiHydrate |
| Potassium Bicarbonate | Epsom Salts | |
| M.O.S.T. | ||
| Sprint 138 and 330 | ||
| S.T.E.M. |
| Products | Item Number | ||
|---|---|---|---|
| Jack’s All Purpose LX 21-5-20 | 33602 | ||
| Peters Excel 21-5-20 Multi-purpose | 67-2308 | ||
| Plantex 21-5-20 High Nitrate Low P | 31-140306 | ||
| Jack’s Peat Lite 20-10-20 | 33615 | ||
| Peters Professional Peat Lite 20-10-20 | 67-2332 | ||
| Plantex All Purpose High Nitrate | 31-140200 | ||
| Jack’s FeED 20-3-19 | 33-20319 | ||
| Peter’s Professional 20-3-19 Petunia Special with Black Iron | 67-2364 | ||
| Plantex Fertility Plus 19-2-19 | 31-11078 | ||
| Jack’s Dark Weather Peat Lite 15-0-15 | 33627 | ||
| Peters Professional 15-0-15 Peat Lite Dark Weather | 67-2340 | ||
| Plantex 15-0-15 Cal-Plus | 31-140100 | ||
| Jack’s Dark Weather Plus Mag LX 15-0-14 | 33-150014 | ||
| Plant-Prod MJ Cal Kick 15-0-14 | 31-M12305 | ||
| Jack’s Plug LX 13-2-13 | 33607 | ||
| Peters Excel 13-2-13 Plug and Bedding Plant Special | 67-2304 | ||
| Jack’s Calcium and Magnesium LX 15-5-15 | 33601 | ||
| Peters Excel 15-5-15 Cal-Mag Special with Black Iron | 67-2305 | ||
| Cal-Ox pH | 75-0525 | ||
| Jack’s Potassium Bicarbonate | 91-2190 | ||
| Plantex Potassium Bicarbonate | 31-10404 | ||
| Sulfuric Acid 93% Tech Grade | 75-5030 | ||
| Calcium Chloride DiHydrate | 35315 | ||
| Giles Epsom Salts | 67-7500GW | ||
| Jack’s Epsom Salts | 33-79160 | ||
| Kirby Agri Epsom Salts | 14GSUL | ||
| M.O.S.T. | J74394 | ||
| Sprint 138 | 67-70371 | ||
| Sprint 330 | 67-70361 | ||
| S.T.E.M. | 67-2366 | ||
Note, not all products are registered in all states. Some pesticides are restricted use in some states or regions and not others. It is the responsibility of the applicator to read and follow all label directions, remembering that labels may change. Other products may be safe and effective. Rates, application methods, and edible status are detailed in our GGSPro Insecticide & Fungicide Guides. Griffin also offers the 5th Edition GGSPro Technical Reference Guide in both English and now Spanish versions. This valuable resource outlines a wide range of pest control options and information on pollinator safety, BCA’s, scouting, weed management, plant lighting, nutrition, water quality and more!