While the first part of the year has been generally mild, temperatures have been unseasonably cool during the first few weeks of spring. Low ambient and substrate temperatures can lead to slower movement and uptake of water and nutrients, which can cause plants to exhibit symptoms of nutrient deficiency.
Slower rates of movement can hinder the uptake of iron (Fe), as well as phosphorus (P). Due to reduced water uptake by plants when temperatures are low, it is easy to overwater and saturate the substrate for a prolonged period. Saturation reduces oxygen levels in the root zone and negatively affects root growth and uptake of nutrients such as iron (Fe), phosphorus (P), calcium (Ca) and boron (B), leading to deficiency symptoms of these nutrient elements. A constantly saturated substrate can also increase the incidence of root diseases such as Pythium and Phytophthora, which can further affect the ability of roots to absorb water and nutrients. Continued application of nutrients into low temperature substrates can also lead to high EC and high soluble salts in the substrate, resulting in marginal leaf necrosis of the lower leaves on plants.
Nutrient problems can show up in a crop very quickly. It is important to perform regular scouting and monitoring (testing) in order to identify problems early and take corrective action if needed. Be sure to check color and vigor of the foliage, as well as the health of the roots. Checking the roots is important because even though the foliage may be showing symptoms of a nutrient problem, the plant may have a compromised root system due to cool substrate temperature, an overwatered substrate, root disease such as Pythium, or pest infestation like fungus gnats rather than an issue with the fertilizer type or concentration.
Conduct regular testing (weekly) of media pH and EC. pH affects the availability of nutrients and EC measures the overall concentration of fertilizer salts in the media. If possible send a substrate sample to a lab for a growing media test to confirm the nutrient element(s) causing deficiency or toxicity symptoms.
The most common and easy method to perform media testing in the greenhouse is the pour-through method:
- Irrigate the crop 1 hour before testing. Select 5 pots and place plastic saucers under them. Pour distilled water on to the surface of the media. The amount of distilled water depends on the size of the pot: For cell packs and 4-inch pots, pour 50 ml (1.7 oz), for 6-inch pots, 75 ml (2.5 oz), and for 6 ½ - 8-inch pots, pour 100 ml (3.3oz). Collect the leachate and test pH and EC as soon as possible.
- The acceptable EC ranges for pour-through (mS/cm) are: Low 1.0 – 2.5; Normal 2.6 – 4.5; High 4.6 – 6.5; above 6.5 can cause root damage.
- The acceptable pH range depends on crop species. For iron-inefficient crops such as petunia, calibrachoa, and pansy, the acceptable pH range is 5.4 – 6.2. For iron-efficient crops, such as zonal geranium, marigolds, and New Guinea impatiens, the acceptable pH range is 6.0 – 6.6. For other crops such as impatiens and ivy geraniums, the acceptable pH range is 6.0 – 6.4. A range of 6.0 – 6.2 is generally acceptable for most crops
Additional tips for troubleshooting and managing nutrient problems:
|
Symptom |
Possible problem |
Solution |
|---|---|---|
|
Older leaves turn purple, top of the plant may be dark green. |
Phosphorus deficiency |
Check P levels in the fertilizer. Drench with fertilizer containing P at 50-100 ppm. |
|
Youngest leaves start to show interveinal chlorosis progressing to yellowing. |
Iron deficiency |
Check media pH, adjust pH by adding acid fertilizer (NH4+). Use supplemental iron chelate drenches. |
|
Growing tip alive, but young leaves are distorted. Leaf edges may become necrotic. |
Calcium deficiency |
Lower humidity levels in the greenhouse. If this doesn’t work use foliar sprays with calcium chloride. |
|
Growing tip is lost, many grow-ing tips develop, young leaves elongate and are brittle. |
Boron deficiency |
Lower humidity levels in the greenhouse. Drench with Borax at 0.85 g/100 gal water. |
|
Older leaves become chlorotic over the entire leaf. |
Nitrogen deficiency |
Check EC of fertilizer solution. Check if injector is working properly. |
|
Stunted plant growth, marginal leaf necrosis of the lower leaves. |
Very high substrate EC (soluble salts) |
Irrigate with clear water allow some leaching to flush the salts. |
For more information on plant nutritional disorders follow the links below:
- Whipker B. E. and P. Cockson, 2020. North Carolina State University. Nutrient Disorder Primer: A quick guide to nutritional disorders. eGRO alert factsheet: http://e-gro.org/pdf/2020_908.pdf
- Njue G. and B. Krug, 2008. University of New Hampshire Extension. Scouting and Managing Greenhouse Nutrient Problems. UNH Extension factsheet: https://extension.unh.edu/resources/files/Resource000887_Rep937.pdf
- Njue G. and B. Krug, 2008. University of New Hampshire Extension. Fertilizer-Injector Calibration. UNH Extension factsheet: https://extension.unh.edu/resources/files/Resource000882_Rep928.pdf
- Geoffrey Njue, Extension Educator, UMass Extension Greenhouse Crops and Floriculture Program
