Bell peppers grown in greenhouse hydroponic systems follow similar environmental requirements as tomatoes and eggplants. It is a common production practice to leave all the leaves on the pepper plants. This creates very tall walls of foliage that slightly affect the plants’ nutritional requirements.
Pepper growth follows generally two different phases during greenhouse production. After the seedlings are transplanted, the first six weeks of production is geared toward developing a strong vegetative base. After fruit set, the nutrient recipe is changed slightly to keep the plants in balance. For peppers only potassium is significantly increased after fruit set occurs.
Table 1. Nutrient solution for hydroponic pepper cultivation.
|0-6 weeks||Mature crop|
|Reference EC||2.2 mS/cm||2.5mS/cm|
|Nitrate (NO3)||200 ppm||180 ppm|
|Ammonium (NH4)||7 ppm||15 ppm|
|Potassium (K)||240 ppm||270-300 ppm (200 ppm*)|
|Phosphate (PO4)||50 ppm||50 ppm|
|Calcium (Ca)||220 ppm||200 ppm (300 ppm*)|
|Magnesium (Mg)||50 ppm||45 ppm|
|Iron (Fe)||1.5 ppm||1 ppm|
|Manganese (Mn)||0.55 ppm||0.55 ppm|
|Zinc (Zn)||0.33 ppm||0.33 ppm|
|Boron (B)||0.3 ppm||0.3 ppm|
|Copper (Cu)||0.05 ppm||0.05 ppm|
|Molybdenum (Mo)||0.05 ppm||0.05 ppm|
|Sulfates (SO4)||20 ppm||20 ppm|
|Chloride (Cl)||<300 ppm||<300 ppm|
|Sodium (Na)||<100 ppm||<100 ppm|
Concentrations in parts per million (ppm) at the dripper. Micronutrients are in shaded boxes. (*) See below for explanation on blossom end rot.
Like all nutrient recipes the numbers in Table 1 are a starting point that will need to be adjusted depending on the local environment (temperature, humidity, solar radiation and water quality) and the different salt accumulations that occur in normal conditions depending on the absorption by any given strain of pepper. Note that the ammonium (NH4) levels for young and mature plants are very low compared to nitrates. Ammonium is not necessary depending on the substrate included for pH buffering.
Note also that chloride and sodium have upper ranges. These two are considered contaminants even if they have nutritional value for the plants. They are generally present in the water and their requirements are very low similar to micronutrients.
Preventing blossom end rot
Bell peppers’ most common physiological problem is blossom end rot, which is generally due to a water stress preventing the internal transport of calcium. It is common to increase the concentration of calcium ions in the solution together with chloride, phosphate and boron while reducing potassium to promote the absorption of calcium during potential blossom end rot periods, particularly during hot summers (* in Table 1).
The most common chemicals for mixing nutrient solution are the following:
- Ca(NO3)2 (Calcium nitrate)
- KNO3 (Potassium nitrate)
- KH2PO4 (Monopotassium phosphate)
- MgSO4*7 H2O (Magnesium sulfate)
- H3BO3 (Boric acid)
- MnCl2*4 H2O (Manganous chloride)
- CuCl2*2 H2O (Cupric chloride)
- K2SO4 (Potassium sulfate)
- MoO3 (Molybdenum trioxide)
- ZnSO4*7 H2O (Zinc sulfate)
- Fe 330 – Sequestrene (chelated iron)
Commonly in hydroponic production, chemicals are mixed in concentrated solutions to be diluted at the time of irrigation. The drawback of this fertilization method is that some of the chemicals present will precipitate out and be removed from the nutrient solution and need to be kept separate in at least two reservoirs. As a common rule, calcium needs to be separated from phosphates and sulfates to prevent precipitation.