Nutrient availability is intricately linked to the pH of the growing medium, influencing how readily plants can absorb essential elements. At varying pH levels, the solubility of nutrients changes, affecting their accessibility; certain nutrients may become more available in slightly acidic conditions, while others may precipitate or become bound in alkaline environments. By maintaining pH within an optimal range, growers can enhance nutrient uptake, ensuring that plants receive the vital elements needed for robust growth and development.
Therefore, it is crucial for growers to have the ability to monitor their pH and electrical conductivity (EC) regularly, as this information allows them to make informed adjustments and promote healthy plant growth. Handheld meters, such as Bluelab’s innovative OnePen, are a convenient and durable option for quickly assessing data in the production space.
Figure 1: Bluelab’s OnePen for measuring pH, EC, and Temperature. Bluetooth compatible.
Poinsettias require an elevated amount of three key nutrients. We call these “The 3 M’s of Poinsettias”: Manganese (Mn), Molybdenum (Mo), and Magnesium (Mg). To avoid a combined problem of reduced availability and low uptake, it’s essential to provide fertilizer sources with ample amounts of these nutrients along with maintaining a soil pH in the range of 6.0-6.5.
We understand not all growers will send regular media or tissue samples in for testing throughout the production season, so it is important to know where these deficiencies might occur and what they look like. The location of a plant deficiency is heavily tied to a nutrient’s mobility within the plant. Nutrients are categorized as mobile, immobile, or intermediate, each affecting plant health in different ways.
Manganese (Mn) Deficiency
Poinsettias with manganese deficiency exhibit symptoms including interveinal chlorosis starting with the youngest growth. The veins will appear sunken while the tissue between the veins looks raised. Frequent media analysis should be conducted to treat before symptoms appear. Maintain media pH below 6.2 to improve manganese availability.
Mn symptoms can be easily confused with iron deficiency. To distinguish Mn deficiency from a Fe deficiency, look for the characteristic change in leaf texture to a corrugated look, sometimes resemblant of an orange peel in appearance. High levels of iron in the media can inhibit the uptake of manganese. If media tests confirm a deficiency, apply a corrective drench of 13% chelated manganese at 1.0-1.5 oz per 100 gal. Retest the media before making additional applications.
Figure 2: Manganese (Mn) deficiency on poinsettia.
Molybdenum (Mo) Deficiency
Molybdenum strays from the general solubility rule for other micronutrients and becomes more available as soil pH rises above 6.0. Growers incorporate poinsettia feeds with molybdenum as a part of the fertilizer regime but will often supplement with additional ammonium molybdate. This is especially true when using standard peat-lite fertilizers. Some of the newer poinsettia cultivars appear to have higher Mo requirements. If you’re not using a fertilizer specifically for poinsettias with elevated Mo, or soil tests indicate Mo is lacking, you can make pulse treatments or opt for a constant injection plan (see below). Foliar sprays are often avoided to prevent phytotoxicity issues.
Table 1: Ammonium Molybdate Drench Rates
Molybdenum deficiencies are slow to express and should be treated preventatively in the months of September and October prior to bract formation. Yellowing along the leaf margins, leaf cupping, and scorch-like distortion typically appear in the middle section of the foliage just below the bracts. Molybdenum applications made after the symptoms appear will unfortunately not reverse these symptoms. Large, well-formed bracts will often hide those symptoms. Growers experiencing low soil pH may have to rely on a foliar spray instead of a soil drench, although correcting the soil pH is recommended.
Figure 3: Molybdenum (Mo) deficiency on poinsettia.
Magnesium (Mg) Deficiency
Magnesium is the central element to the chlorophyll molecule and is very mobile in the plant. Thus, deficiency symptoms begin with interveinal chlorosis in the lower foliage. Downward cupping and a thicker texture may also occur with more severe deficiencies. Magnesium deficiency is often an indication that the overall fertility level of the crop is too low.
Apply magnesium as a one-time corrective drench application or as a part of a constant liquid feed program. Epsom salts (magnesium sulfate) are an inexpensive option and can be added to most fertilizers except for those containing calcium (e.g., 15-0-15, 15-5-15, 13-2-13). The one-time corrective rate for Epsom salts is 6-8 oz per 100 gal. Constant injection of Epsom salts can be done at lower rates, generally 2-3 oz per 100 gal (or 2-3 oz per gal at 1:100 injection) based on the amount of magnesium in the irrigation water, including the fertilizer.
Figure 4: Magnesium (Mg) deficiency on poinsettia.
Table 2: Products for Poinsettia Nutrition
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!
Therefore, it is crucial for growers to have the ability to monitor their pH and electrical conductivity (EC) regularly, as this information allows them to make informed adjustments and promote healthy plant growth. Handheld meters, such as Bluelab’s innovative OnePen, are a convenient and durable option for quickly assessing data in the production space.
Figure 1: Bluelab’s OnePen for measuring pH, EC, and Temperature. Bluetooth compatible.
Poinsettias require an elevated amount of three key nutrients. We call these “The 3 M’s of Poinsettias”: Manganese (Mn), Molybdenum (Mo), and Magnesium (Mg). To avoid a combined problem of reduced availability and low uptake, it’s essential to provide fertilizer sources with ample amounts of these nutrients along with maintaining a soil pH in the range of 6.0-6.5.
We understand not all growers will send regular media or tissue samples in for testing throughout the production season, so it is important to know where these deficiencies might occur and what they look like. The location of a plant deficiency is heavily tied to a nutrient’s mobility within the plant. Nutrients are categorized as mobile, immobile, or intermediate, each affecting plant health in different ways.
- Mobile nutrients move easily within the plant. The lower leaves can give up these nutrients to supply the younger leaves. Therefore, deficiency symptoms are first expressed on the lower leaves of the plant. Mobile nutrients include nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg).
- Immobile nutrients don’t move easily through the plant. The lower leaves are unable to supply nutrients to the upper, newer foliage. Deficiency symptoms first express on the youngest leaves for immobile nutrients like boron (B), calcium (Ca), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn).
- Nutrients with intermediate mobility can exhibit early deficiency symptoms anywhere on the plant. Somewhat mobile nutrients include molybdenum (Mo) and sulfur (S).
Manganese (Mn) Deficiency
Poinsettias with manganese deficiency exhibit symptoms including interveinal chlorosis starting with the youngest growth. The veins will appear sunken while the tissue between the veins looks raised. Frequent media analysis should be conducted to treat before symptoms appear. Maintain media pH below 6.2 to improve manganese availability.
Mn symptoms can be easily confused with iron deficiency. To distinguish Mn deficiency from a Fe deficiency, look for the characteristic change in leaf texture to a corrugated look, sometimes resemblant of an orange peel in appearance. High levels of iron in the media can inhibit the uptake of manganese. If media tests confirm a deficiency, apply a corrective drench of 13% chelated manganese at 1.0-1.5 oz per 100 gal. Retest the media before making additional applications.
Figure 2: Manganese (Mn) deficiency on poinsettia.
Molybdenum (Mo) Deficiency
Molybdenum strays from the general solubility rule for other micronutrients and becomes more available as soil pH rises above 6.0. Growers incorporate poinsettia feeds with molybdenum as a part of the fertilizer regime but will often supplement with additional ammonium molybdate. This is especially true when using standard peat-lite fertilizers. Some of the newer poinsettia cultivars appear to have higher Mo requirements. If you’re not using a fertilizer specifically for poinsettias with elevated Mo, or soil tests indicate Mo is lacking, you can make pulse treatments or opt for a constant injection plan (see below). Foliar sprays are often avoided to prevent phytotoxicity issues.
| Treatment | Rate | Application Notes |
|---|---|---|
| Pulse Treatment x 2 | 3.25 oz stock per 1 gal fertilizer concentrate; inject at 1:100 | Apply once in mid-September and once in mid-October |
| Periodic Treatment | 1.5 oz stock per 1 gal fertilizer concentrate; inject at 1:100 | Apply every two weeks if media test indicates deficiency |
| Constant Injection | 1.5 oz stock per 10 gal fertilizer concentrate; inject at 1:100 | Apply every two weeks if media test indicates deficiency |
Molybdenum deficiencies are slow to express and should be treated preventatively in the months of September and October prior to bract formation. Yellowing along the leaf margins, leaf cupping, and scorch-like distortion typically appear in the middle section of the foliage just below the bracts. Molybdenum applications made after the symptoms appear will unfortunately not reverse these symptoms. Large, well-formed bracts will often hide those symptoms. Growers experiencing low soil pH may have to rely on a foliar spray instead of a soil drench, although correcting the soil pH is recommended.
Figure 3: Molybdenum (Mo) deficiency on poinsettia.
Magnesium (Mg) Deficiency
Magnesium is the central element to the chlorophyll molecule and is very mobile in the plant. Thus, deficiency symptoms begin with interveinal chlorosis in the lower foliage. Downward cupping and a thicker texture may also occur with more severe deficiencies. Magnesium deficiency is often an indication that the overall fertility level of the crop is too low.
Apply magnesium as a one-time corrective drench application or as a part of a constant liquid feed program. Epsom salts (magnesium sulfate) are an inexpensive option and can be added to most fertilizers except for those containing calcium (e.g., 15-0-15, 15-5-15, 13-2-13). The one-time corrective rate for Epsom salts is 6-8 oz per 100 gal. Constant injection of Epsom salts can be done at lower rates, generally 2-3 oz per 100 gal (or 2-3 oz per gal at 1:100 injection) based on the amount of magnesium in the irrigation water, including the fertilizer.
Figure 4: Magnesium (Mg) deficiency on poinsettia.
| Product Description | Item Number |
|---|---|
| Bluelab OnePen | 83-2707 |
| Ammonium Heptamolybdate (Jack’s) | J74744 |
| Magnesium Sulfate/ Epsom Salts | 14MGSUL |
| Manganese Chelate (Brandt) 13% | 67-04305 |
| Manganese Sulfate (Plantex) 32% | 31-10271 |
| M.O.S.T Micronutrients (Jack’s) | J74394 |
| Poinsettia FeED Plus Mg 17-5-19 (Jack’s) | 3317519 |
| Poinsettia FeED Ca-Mg 15-4-15 (Jack’s) | 3315415 |
| Poinsettia Plus 18-6-20 (Plantex) | 31-140151 |
| S.T.E.M Micronutrients (ICL Peters) | 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!